LTC1992-10IMS8#PBF [Linear]
LTC1992 Family - Low Power, Fully Differential Input/Output Amplifier/Driver Family; Package: MSOP; Pins: 8; Temperature Range: -40°C to 85°C;
| 型号： | LTC1992-10IMS8#PBF |
| 厂家： | 
Linear |
| 描述： | LTC1992 Family - Low Power, Fully Differential Input/Output Amplifier/Driver Family; Package: MSOP; Pins: 8; Temperature Range: -40°C to 85°C 放大器 光电二极管 |
| 文件： | 总40页 (文件大小：505K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1992 Family
Low Power, Fully Differential
Input/Output
Amplifier/Driver Family
U
FEATURES
DESCRIPTIO
The LTC®1992 product family consists of five fully differ-
ential, low power amplifiers. The LTC1992 is an uncon-
strained fully differential amplifier. The LTC1992-1,
LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain
blocks (with gains of 1, 2, 5 and 10 respectively) featuring
precision on-chip resistors for accurate and ultrastable
gain. All of the LTC1992 parts have a separate internal
common mode feedback path for outstanding output
phase balancing and reduced second order harmonics.
The VOCM pin sets the output common mode level inde-
pendent of the input common mode level. This feature
makes level shifting of signals easy.
■
Adjustable Gain and Fixed Gain Blocks of 1, 2, 5
and 10
■
±0.3% (Max) Gain Error from –40°C to 85°C
■
3.5ppm/°C Gain Temperature Coefficient
■
5ppm Gain Long Term Stability
■
Fully Differential Input and Output
■
CLOAD Stable up to 10,000pF
■
Adjustable Output Common Mode Voltage
■
Rail-to-Rail Output Swing
■
Low Supply Current: 1mA (Max)
■
High Output Current: 10mA (Min)
■
Specified on a Single 2.7V to ±5V Supply
■
DC Offset Voltage <2.5mV (Max)
Available in 8-Lead MSOP Package
The amplifiers’ differential inputs operate with signals
ranging from rail-to-rail with a common mode level from
the negative supply up to 1.3V from the positive supply.
The differential input DC offset is typically 250µV. The rail-
to-rail outputs sink and source 10mA. The LTC1992 is
stable for all capacitive loads up to 10,000pF.
■
U
APPLICATIO S
■
Differential Driver/Receiver
■
Differential Amplification
The LTC1992 can be used in single supply applications
with supply voltages as low as 2.7V. It can also be used
with dual supplies up to ±5V. The LTC1992 is available in
an 8-pin MSOP package.
■
Single-Ended to Differential Conversion
Level Shifting
Trimmed Phase Response for Multichannel Systems
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
U
TYPICAL APPLICATIO
Single-Supply, Single-Ended to Differential Conversion
10k
5V
5V
5V
V
3
IN
0V
5V
2.5V
0V
(5V/DIV)
10k
4
1
7
V
IN
+
MID
0V
–
–5V
5V
V
+OUT
(2V/DIV)
–OUT
LTC1992
–5V
2
8
V
OCM
5V
2.5V
0V
10k
+
–
6
5
0.01µF
0V
OUTPUT SIGNAL
FROM A
SINGLE-SUPPLY SYSTEM
INPUT SIGNAL
FROM A
±5V SYSTEM
10k
1992 TA01b
1992 TA01a
1992f
1
LTC1992 Family
W W U W
ABSOLUTE AXI U RATI GS
(Note 1)
Total Supply Voltage (+VS to –VS) .......................... 12V
Maximum Voltage
Specified Temperature Range (Note 6)
LTC1992CMS8/LTC1992-XCMS8/
on any Pin .......... (–VS – 0.3V) ≤ VPIN ≤ (+VS + 0.3V)
Output Short-Circuit Duration (Note 3)............ Indefinite
Operating Temperature Range (Note 5)
LTC1992IMS8/LTC1992-XIMS8 ..........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 .....–40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LTC1992CMS8/LTC1992-XCMS8/
LTC1992IMS8/LTC1992-XIMS8 ..........–40°C to 85°C
LTC1992HMS8/LTC1992-XHMS8 .....–40°C to 125°C
U W
U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
–IN
1
2
3
4
8 +IN
7 V
–IN
1
2
3
4
8 +IN
7 V
V
V
OCM
MID
OCM
MID
+
–
+
–
6 –V
+V
S
6 –V
+V
S
S
S
+
–
+
–
5 –OUT
+OUT
5 –OUT
+OUT
MS8 PACKAGE
8-LEAD PLASTIC MSOP
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 250°C/W
TJMAX = 150°C, θJA = 250°C/W
ORDER PART
NUMBER
MS8 PART
MARKING
ORDER PART
NUMBER
MS8 PART
MARKING
LTYU
LTZC
LTAGR
LTC1992CMS8
LTC1992IMS8
LTC1992HMS8
LTC1992-1CMS8
LTC1992-1IMS8
LTC1992-1HMS8
LTC1992-2CMS8
LTC1992-2IMS8
LTC1992-2HMS8
LTC1992-5CMS8
LTC1992-5IMS8
LTC1992-5HMS8
LTC1992-10CMS8
LTC1992-10IMS8
LTC1992-10HMS8
LTACJ
LTACM
LTAFZ
LTYV
LTZD
LTAGA
LTACK
LTACN
LTAJH
LTACL
LTACP
LTAJJ
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1992f
2
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
ALL C AND I GRADE
ALL H GRADE
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
V
Supply Voltage Range
Supply Current
●
2.7
11
2.7
11
V
S
I
V = 2.7V to 5V
0.65
0.75
0.7
1.0
1.2
1.2
1.5
0.65
0.8
0.7
0.9
1.0
1.5
1.2
1.8
mA
mA
mA
mA
S
S
●
●
V = ±5V
S
0.8
V
Differential Offset Voltage
(Input Referred) (Note 7)
V = 2.7V
●
●
●
±0.25 ±2.5
±0.25 ±2.5
±0.25 ±2.5
±0.25
±0.25
±0.25
±4
±4
±4
mV
mV
mV
OSDIFF
S
V = 5V
S
V = ±5V
S
∆V
OSDIFF
/∆T Differential Offset Voltage Drift
V = 2.7V
●
●
●
10
10
10
10
10
10
µV/°C
µV/°C
µV/°C
S
(Input Referred) (Note 7)
V = 5V
S
V = ±5V
S
PSRR
Power Supply Rejection Ratio
(Input Referred) (Note 7)
V = 2.7V to ±5V
S
●
75
80
72
80
dB
G
CM
Common Mode Gain(V
/V
)
●
●
●
1
±0.1
–85
1
OUTCM OCM
Common Mode Gain Error
Output Balance (∆V /(∆V
±0.3
–60
±0.1 ±0.35
–85
%
dB
) V = –2V to +2V
OUTDIFF
–60
OUTCM
OUTDIFF
V
Common Mode Offset Voltage
(V – V
V = 2.7V
●
●
●
±0.5
±1
±2
±12
±15
±18
±0.5
±1
±2
±15
±17
±20
mV
mV
mV
OSCM
S
)
V = 5V
OUTCM
OCM
S
V = ±5V
S
∆V
OSCM
/∆T
Common Mode Offset Voltage Drift
V = 2.7V
●
●
●
10
10
10
10
10
10
µV/°C
µV/°C
µV/°C
S
V = 5V
S
V = ±5V
S
V
Output Signal Common Mode Range
●
(–V )+0.5V
(+V )–1.3V (–V )+0.5V
(+V )–1.3V
V
OUTCMR
S
S
S
S
(Voltage Range for the V
Pin)
OCM
R
Input Resistance, V
Pin
●
●
●
500
500
±2
MΩ
pA
V
INVOCM
OCM
I
Input Bias Current, V
Pin
V = 2.7V to ±5V
±2
BVOCM
OCM
S
V
V
Voltage at the V
Pin
2.44
2.50
2.56
2.43
2.50
2.57
MID
OUT
MID
Output Voltage, High
(Note 2)
V = 2.7V, Load = 10k
●
●
●
2.60
2.50
2.29
2.69
2.61
2.52
2.60
2.50
2.29
2.69
2.61
2.52
V
V
V
S
V = 2.7V, Load = 5mA
S
V = 2.7V,Load = 10mA
S
Output Voltage, Low
(Note 2)
V = 2.7V, Load = 10k
●
●
●
0.02
0.10
0.20
0.10
0.25
0.35
0.02
0.10
0.20
0.10
0.25
0.41
V
V
V
S
V = 2.7V, Load = 5mA
S
V = 2.7V, Load = 10mA
S
Output Voltage, High
(Note 2)
V = 5V, Load = 10k
●
●
●
4.90
4.85
4.75
4.99
4.90
4.81
4.90
4.80
4.70
4.99
4.90
4.81
V
V
V
S
V = 5V, Load = 5mA
S
V = 5V, Load = 10mA
S
Output Voltage, Low
(Note 2)
V = 5V, Load = 10k
●
●
●
0.02
0.10
0.20
0.10
0.25
0.35
0.02
0.10
0.20
0.10
0.30
0.42
V
V
V
S
V = 5V, Load = 5mA
S
V = 5V, Load = 10mA
S
Output Voltage, High
(Note 2)
V = ±5V, Load = 10k
●
●
●
4.90
4.85
4.65
4.99
4.89
4.80
4.85
4.80
4.60
4.99
4.89
4.80
V
V
V
S
V = ±5V, Load = 5mA
S
V = ±5V, Load = 10mA
S
Output Voltage, Low
(Note 2)
V = ±5V, Load = 10k
●
●
●
–4.99 –4.90
–4.90 –4.75
–4.80 –4.65
–4.98 –4.85
–4.90 –4.75
–4.80 –4.55
V
V
V
S
V = ±5V, Load = 5mA
S
V = ±5V, Load = 10mA
S
1992f
3
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Specifications applicable to all parts in the LTC1992 family.
ALL C AND I GRADE
ALL H GRADE
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
I
Output Short-Circuit Current
Sourcing (Notes 2,3)
V = 2.7V, V
= 1.35V
= 2.5V
= 0V
●
●
●
20
20
20
30
30
30
20
20
20
30
30
30
mA
mA
mA
SC
S
OUT
V = 5V, V
S
OUT
V = ±5V, V
S
OUT
Output Short-Circuit Current Sinking V = 2.7V, V
=1.35V
OUT
= 2.5V
●
●
●
13
13
13
30
30
30
13
13
13
30
30
30
mA
mA
mA
S
(Notes 2,3)
V = 5V, V
V = ±5V, V
S
OUT
= 0V
OUT
S
A
Large-Signal Voltage Gain
●
80
80
dB
VOL
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Specifications applicable to the LTC1992 only.
LTC1992CMS8
LTC1992ISM8
LTC1992HMS8
SYMBOL
PARAMETER
CONDITIONS
V = 2.7V to ±5V
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
pA
I
I
Input Bias Current
Input Offset Current
Input Resistance
Input Capacitance
●
●
●
●
2
250
100
2
400
150
B
S
V = 2.7V to ±5V
S
0.1
500
3
0.1
500
3
pA
OS
R
IN
MΩ
pF
C
IN
e
Input Referred Noise Voltage Density f = 1kHz
35
1
35
1
nV/√Hz
fA/√Hz
V
n
i
Input Noise Current Density
f = 1kHz
n
V
Input Signal Common Mode Range
●
●
(–V )– 0.1V (+V )– 1.3V (–V )– 0.1V (+V )– 1.3V
INCMR
S
S
S
S
CMRR
Common Mode Rejection Ratio
(Input Referred)
V
= –0.1V to 3.7V
69
90
69
90
dB
INCM
SR
Slew Rate (Note 4)
●
0.5
1.5
0.5
3.0
1.5
3.2
V/µs
GBW
Gain-Bandwidth Product
T = 25°C
3.0
2.5
1.9
3.2
3.0
3.5
4.0
4.0
3.5
4.0
MHz
MHz
MHz
A
(f
TEST
= 100kHz)
LTC1992CMS8
LTC1992IMS8/
LTC1992HMS8
●
●
1.9
1992f
4
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-1 only.
LTC1992-1CMS8
LTC1992-1IMS8
LTC1992-1HMS8
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
G
DIFF
Differential Gain
1
1
V/V
%
Differential Gain Error
●
●
±0.1
50
±0.3
±0.1 ±0.35
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
50
3.5
ppm
3.5
ppm/°C
e
Input Referred Noise Voltage Density (Note 7) f = 1kHz
Input Resistance, Single-Ended +IN, –IN Pins
45
30
45
nV/√Hz
kΩ
n
R
●
22.5
37.5
22
30
– 0.1V to 4.9V
60
38
IN
V
Input Signal Common Mode Range
V = 5V
S
– 0.1V to 4.9V
60
V
INCMR
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
V
= –0.1V to 3.7V
●
●
55
55
dB
INCM
SR
Slew Rate (Note 4)
0.5
1.5
3
0.5
1.5
3
V/µs
GBW
Gain-Bandwidth Product
f
= 180kHz
MHz
TEST
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-2 only.
LTC1992-2CMS8
LTC1992-2IMS8
LTC1992-2HMS8
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
G
DIFF
Differential Gain
2
2
V/V
%
Differential Gain Error
●
●
±0.1
50
±0.3
±0.1 ±0.35
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
50
3.5
ppm
3.5
ppm/°C
e
Input Referred Noise Voltage Density (Note 7) f = 1kHz
Input Resistance, Single-Ended +IN, –IN Pins
45
30
45
nV/√Hz
kΩ
n
R
●
22.5
37.5
22
30
– 0.1V to 4.9V
60
38
IN
V
Input Signal Common Mode Range
V = 5V
S
– 0.1V to 4.9V
60
V
INCMR
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
V
= –0.1V to 3.7V
●
●
55
55
dB
INCM
SR
Slew Rate (Note 4)
0.7
2
4
0.7
2
4
V/µs
GBW
Gain-Bandwidth Product
f
= 180kHz
MHz
TEST
1992f
5
LTC1992 Family
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. +VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise
noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is
defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT). Typical values are at TA = 25°C. Specifications apply to the
LTC1992-5 only.
LTC1992-5CMS8
LTC1992-5IMS8
LTC1992-5HMS8
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
G
DIFF
Differential Gain
5
5
V/V
%
Differential Gain Error
●
●
±0.1
50
±0.3
±0.1 ±0.35
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
50
3.5
ppm
3.5
ppm/°C
e
Input Referred Noise Voltage Density (Note 7) f = 1kHz
Input Resistance, Single-Ended +IN, –IN Pins
45
30
45
nV/√Hz
kΩ
n
R
●
22.5
37.5
22
30
– 0.1V to 3.9V
60
38
IN
V
Input Signal Common Mode Range
V = 5V
S
– 0.1V to 3.9V
60
V
INCMR
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
V
= –0.1V to 3.7V
●
●
55
55
dB
INCM
SR
Slew Rate (Note 4)
0.7
2
4
0.7
2
4
V/µs
GBW
Gain-Bandwidth Product
f
= 180kHz
MHz
TEST
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
+VS = 5V, –VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as
(+VOUT + –VOUT)/2. VINCM is defined as (+VIN + –VIN)/2. VINDIFF is defined as (+VIN – –VIN). VOUTDIFF is defined as (+VOUT – –VOUT).
Typical values are at TA = 25°C. Specifications apply to the LTC1992-10 only.
LTC1992-10CMS8
LTC1992-10IMS8
LTC1992-10HMS8
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
G
DIFF
Differential Gain
10
±0.1
50
10
V/V
%
Differential Gain Error
●
●
±0.3
±0.1 ±0.35
Differential Gain Nonlinearity
Differential Gain Temperature Coefficient
50
3.5
ppm
3.5
ppm/°C
e
Input Referred Noise Voltage Density (Note 7) f = 1kHz
Input Resistance, Single-Ended +IN, –IN Pins
45
15
45
nV/√Hz
kΩ
n
R
●
11.3
18.8
11
15
– 0.1V to 3.8V
60
19
IN
V
Input Signal Common Mode Range
V = 5V
S
– 0.1V to 3.8V
60
V
INCMR
CMRR
Common Mode Rejection Ratio
(Amplifier Input Referred) (Note 7)
V
= –0.1V to 3.7V
●
●
55
55
dB
INCM
SR
Slew Rate (Note 4)
0.7
2
4
0.7
2
4
V/µs
GBW
Gain-Bandwidth Product
f
= 180kHz
MHz
TEST
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 6: The LTC1992C/LTC1992-XC are guaranteed to meet the specified
performance limits over the 0°C to 70°C temperature range and are
designed, characterized and expected to meet the specified performance
limits over the –40°C to 85°C temperature range but are not tested or QA
sampled at these temperatures. The LTC1992I/LTC1992-XI are guaranteed
to meet the specified performance limits over the –40°C to 85°C
temperature range. The LTC1992H/LTC1992-XH are guaranteed to meet
the specified performance limits over the –40°C to 125°C temperature
range.
Note 7: Differential offset voltage, differential offset voltage drift, CMRR,
noise voltage density and PSRR are referred to the internal amplifier’s
input to allow for direct comparison of gain blocks with discrete
amplifiers.
Note 2: Output load is connected to the midpoint of the +V and –V
S
S
potentials. Measurement is taken single-ended, one output loaded at a
time.
Note 3: A heat sink may be required to keep the junction temperature
below the absolute maximum when the output is shorted indefinitely.
Note 4: Differential output slew rate. Slew rate is measured single ended
and doubled to get the listed numbers.
Note 5: The LTC1992C/LTC1992-XC/LTC1992I/LTC1992-XI are guaranteed
functional over an operating temperature of –40°C to 85°C. The
LTC1992H/LTC1992-XH are guaranteed functional over the extended
operating temperature of –40°C to 125°C.
1992f
6
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to all parts in the LTC1992 family.
Differential Input Offset Voltage
Common Mode Offset Voltage
Supply Current vs Supply Voltage
vs Temperature (Note 7)
vs Temperature
4
0.6
0.4
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
V
V
= 0V
= 0V
V
V
= 0V
= 0V
INCM
OCM
125°C
85°C
INCM
OCM
3
2
V
S
= ±5V
0.2
25°C
1
V
= ±2.5V
S
0
0
–40°C
V
= ±1.35V
V
= ±1.35V
S
S
–1
–2
–3
–4
–0.2
–0.4
–0.6
–0.8
V
= ±2.5V
S
V
= ±5V
S
–5
0
1
2
3
4
5
6
7
8
9
10
–40
25
85
TEMPERATURE (°C)
125
–40
25
125
85
TEMPERATURE (°C)
TOTAL SUPPLY VOLTAGE (V)
1992 G01
1992 G02
1992 G03
Common Mode Offset Voltage
vs VOCM Voltage
Common Mode Offset Voltage
vs VOCM Voltage
Common Mode Offset Voltage
vs VOCM Voltage
5
0
5
5
0
125°C
125°C
125°C
85°C
25°C
85°C
25°C
0
85°C
25°C
–40°C
–5
–5
–5
–40°C
–40°C
–10
–15
–20
–10
–15
–20
–10
–15
–20
+V = 5V
S
+V = 5V
S
+V = 2.7V
S
–V = 0V
S
–V = –5V
S
–V = 0V
S
V
INCM
= 2.5V
V
= 0V
INCM
V
INCM
= 1.35V
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
–5 –4 –3 –2 –1
0
1
2
3
4
5
0
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
VOLTAGE (V)
V
V
VOLTAGE (V)
V VOLTAGE (V)
OCM
OCM
OCM
1992 G05
1992 G06
1992 G04
Output Voltage Swing
vs Output Load, VS = 2.7V
Output Voltage Swing
vs Output Load, VS = 5V
5.00
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.70
2.65
2.60
2.55
2.50
2.45
2.40
2.35
2.30
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
4.95
4.90
4.85
4.80
4.75
4.70
4.65
4.60
4.55
4.50
125°C
125°C
85°C
25°C
–40°C
25°C
85°C
25°C
–40°C
85°C
125°C
25°C
85°C
125°C
–40°C
–40°C
–20
–5
0
5
10 15 20
–15 –10
0
5
–20 –15 –10 –5
10 15 20
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1992 G08
1992 G07
1992f
7
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to all parts in the LTC1992 family.
Output Voltage Swing
vs Output Load, VS = ±5V
V
OCM Input Bias Current
Differential Input Offset Voltage
vs Time (Normalized to t = 0)
vs VOCM Voltage
10E-9
1E-9
5.0
4.9
4.8
4.7
4.6
4.5
4.4
–3.8
–4.0
–4.2
–4.4
–4.6
–4.8
–5.0
100
TEMP = 35°C
80
60
40
20
0
125°C
–40°C
25°C
100E-12
10E-12
1E-12
85°C
125°C
85°C
25°C
85°C
–20
–40
125°C
–40°C
25°C
–60
–80
+V = 5V
S
–40°C
–V = 0V
S
INCM
V
= 2.5V
100E-15
–100
5
10
–20 –15 –10 –5
0
15 20
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
800
TIME (HOURS)
0
400
1200
1600
2000
LOAD CURRENT (mA)
V
VOLTAGE (V)
OCM
1992 G10
1992 G09
1992 G11
Differential Gain vs Time
(Normalized to t = 0)
Input Common Mode Overdrive
Recovery (Expanded View)
Input Common Mode Overdrive
Recovery (Detailed View)
10
8
TEMP = 35°C
BOTH INPUTS
(INPUTS TIED TOGETHER)
BOTH INPUTS
(INPUTS TIED
TOGETHER)
6
4
2
0
OUTPUTS
OUTPUTS
–2
–4
–6
–8
–10
+V = 2.5V
+V = 2.5V
S
S
–V = –2.5V
–V = –2.5V
S
S
OCM
V
= 0V
V
OCM
= 0V
LTC1992-10 SHOWN
FOR REFERENCE
LTC1992-10 SHOWN
FOR REFERENCE
1992 G13
1992 G14
800
TIME (HOURS)
0
400
1200
1600
2000
50µs/DIV
1µs/DIV
1992 G12
Output Overdrive Recovery
(Detailed View)
Output Overdrive Recovery
(Expanded View)
+V = 2.5V, –V = –2.5V, V
= 0V
S
S
OCM
INPUTS
OUTPUTS
INPUTS OUTPUTS
+V = 2.5V
S
–V = –2.5V
S
OCM
V
= 0V
LTC1992-2 SHOWN
FOR REFERENCE
LTC1992-2 SHOWN FOR REFERENCE
1992 G16
1992 G15
5µs/DIV
50µs/DIV
1992f
8
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992 only.
Differential Input Differential
Single-Ended Input Differential
Differential Phase Response
vs Frequency
Gain vs Frequency, VS = ±2.5V
Gain vs Frequency, VS = ±2.5V
12
6
0
12
6
0
0
–20
R
= R = 10k
FB
R
= R = 10k
IN FB
IN
R
= R = 10k
FB
IN
–40
–6
–6
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–60
–80
C
=
LOAD
–100
–120
–140
–160
–180
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
= 10pF
= 10pF
10
100
1000
10000
10
100
1000
10000
10
100
FREQUENCY (kHz)
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
1992 G17
1992 G18
1992 G37
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
1.5
2.0
1.5
2.0
1.5
+V = 2.7V
S
+V = 5V
S
+V = 5V
S
–V = 0V
S
–V = –5V
S
–V = 0V
S
V
= 1.35V
V
= 0V
OCM
V
OCM
= 2.5V
OCM
1.0
1.0
1.0
0.5
0.5
0.5
–40°C
–40°C
–40°C
0
0
0
125°C
125°C
125°C
25°C
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
85°C
25°C
85°C
25°C
85°C
0.6
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1922 G21
–5 –4 –3 –2 –1
0
1
2
3
4
5
0
0.3
0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1922 G20
COMMON MODE VOLTAGE (V)
1922 G22
Common Mode Rejection Ratio
vs Frequency (Note 7)
Power Supply Rejection Ratio
vs Frequency (Note 7)
Output Balance vs Frequency
120
100
90
0
–20
–40
–60
–80
–100
∆V
∆V
∆V
∆V
∆V
AMPCM
OUTCM
S
∆V
AMPDIFF
OUTDIFF
AMPDIFF
100
80
80
–V
S
70
+V
S
60
50
60
40
40
30
20
10
0
20
0
100
1k
10k
100k
1M
10
100
1k
10k
100k
1M
1
10
100
1k
10k 100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
1992 G23
1992 G24
1992 G25
1992f
9
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992 only.
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
+V = 2.5V
S
+V = 2.5V
S
–V = –2.5V
S
–V = –2.5V
S
V
IN
–V
= 0V
V
= 0V
OCM
OCM
IN
IN
+V = ±1.5V
+V = ±1.5V
±
±
=
1.5V
–V
C
=
1.5V
IN
GAIN = 1
= 0pF
LOAD
GAIN = 1
0V
0V
2.5V
0V
C
LOAD
C
LOAD
= 10000pF
= 1000pF
1992 G27
1992 G26
20µs/DIV
2µs/DIV
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
+V = 5V
+V = 5V
S
–V = 0V
S
S
–V = 0V
S
OCM
V
= 2.5V
+V = 0V TO 4V
V
= 2.5V
OCM
+V = 0V TO 4V
IN
IN
–V = 2V
–V = 2V
IN
GAIN = 1
IN
C
= 0pF
LOAD
GAIN = 1
2.5V
C
LOAD
C
LOAD
= 10000pF
= 1000pF
1992 G28
1992 G29
2µs/DIV
20µs/DIV
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
+V = 2.5V
+V = 2.5V
S
–V = –2.5V
S
S
–V = –2.5V
S
OCM
V
= 0V
V
= 0V
OCM
IN
IN
+V = ±50mV
+V = ±50mV
IN
IN
±
±
–V
=
50mV
= 0pF
–V
GAIN = 1
= 50mV
C
LOAD
GAIN = 1
0V
C
LOAD
C
LOAD
= 10000pF
= 1000pF
1992 G30
1992 G31
1µs/DIV
10µs/DIV
1992f
10
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
C
C
= 10000pF
= 1000pF
LOAD
LOAD
2.5V
2.5V
+V = 5V
S
+V = 5V
–V = 0V
S
S
OCM
–V = 0V
V
= 2.5V
S
OCM
V
= 2.5V
+V = 0V TO 200mV
IN
+V = 0V TO 200mV
–V = 100mV
IN
IN
–V = 100mV
IN
C
= 0pF
LOAD
GAIN = 1
GAIN = 1
1992 G33
1992 G32
10µs/DIV
1µs/DIV
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–50
–60
–70
–80
–90
–100
500kHz MEASUREMENT BANDWIDTH
500kHz MEASUREMENT BANDWIDTH
+V = 5V
S
+V = 5V
S
–V = –5V
S
–50
–60
–V = –5V
S
V
= 0V
OCM
V
OCM
= 0V
V
= 10V
OUT
P-PDIFF
= 5V
P-PDIFF
50kHz
V
OUT
20kHz
–70
V
V
= 1V
OUT
OUT
P-PDIFF
P-PDIFF
10kHz
5kHz
–80
= 2V
–90
2kHz
1kHz
–100
100
1k
10k
50k
0.1
1
10 20
FREQUENCY (Hz)
INPUT SIGNAL AMPLITUDE (V
)
P-PDIFF
1992 G35
1992 G34
Differential Noise Voltage Density
vs Frequency
VOCM Gain vs Frequency,
VS = ±2.5V
1000
100
10
5
0
C
= 10pF TO 10000pF
LOAD
–5
–10
–15
–20
–25
–30
–35
10
100
1000
10000
10
100
1000
10000
FREQUENCY (Hz)
FREQUENCY (kHz)
1922 G36
1992 G19
1992f
11
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-1 only.
Differential Phase Response
vs Frequency
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
12
6
0
12
6
0
0
–20
–6
–6
–40
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–60
–80
C
=
LOAD
–100
–120
–140
–160
–180
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
= 10pF
= 10pF
10
100
1000
10000
10
100
1000
10000
10
100
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
1992 G38
1992 G39
1992 G40
Differential Gain Error vs
Temperature
VOCM Gain vs Frequency
0.025
0.020
0.015
0.010
0.005
0
5
0
C
= 10pF TO 10000pF
LOAD
–5
–10
–15
–20
–25
–30
–35
–0.005
–0.010
–0.015
–0.020
–0.025
–50
0
25
50
75 100 125
–25
10
100
1000
10000
TEMPERATURE (°C)
FREQUENCY (kHz)
1992 G42
1992 G41
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
5
4
5
4
5
4
+V = 5V
S
+V = 2.7V
S
+V = 5V
S
–V = –5V
S
–V = 0V
S
–V = 0V
S
V
= 0V
V
OCM
= 1.35V
V
OCM
= 2.5V
OCM
3
3
3
2
2
2
1
1
1
125°C
85°C
–40°C
–40°C
0
0
0
–40°C
125°C
125°C
–1
–2
–3
–4
–5
–1
–2
–3
–4
–5
–1
–2
–3
–4
–5
25°C
25°C
85°C
25°C
85°C
0.6
–3
0
0.3
0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1922 G43
–5 –4
–2 –1
0
1
2
3
4
5
1.0
0
0.5
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
COMMON MODE VOLTAGE (V)
1922 G45
1922 G44
1992f
12
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-1 only.
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency
100
90
80
70
60
50
40
30
20
10
0
+V = 2.5V
S
–V = –2.5V
S
+V = 2.5V
S
–V = –2.5V
S
V
IN
–V
= 0V
V
= 0V
OCM
OCM
IN
IN
+V = ±1.5V
+V = ±1.5V
±
±
=
1.5V
–V
C
=
1.5V
IN
= 0pF
LOAD
0V
2.5V
0V
0V
C
LOAD
C
LOAD
= 10000pF
= 1000pF
∆V
AMPCM
∆V
AMPDIFF
1992 G47
1992 G46
20µs/DIV
2µs/DIV
100
1k
10k
100k
1M
FREQUENCY (Hz)
1992 G48
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency
100
90
+V = 5V
+V = 5V
S
–V = 0V
S
S
–V = 0V
S
OCM
V
= 2.5V
V
= 2.5V
OCM
80
+V = 0V TO 4V
+V = 0V TO 4V
IN
–V = 2V
IN
–V = 2V
IN
IN
70
–V
S
C
= 0pF
LOAD
60
50
+V
S
2.5V
40
30
20
10
0
C
LOAD
C
LOAD
= 10000pF
= 1000pF
∆V
S
∆V
AMPDIFF
1992 G49
1992 G50
10
100
1k
10k
100k
1M
2µs/DIV
20µs/DIV
FREQUENCY (Hz)
1992 G51
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Output Balance vs Frequency
0
–20
–40
+V = 2.5V
S
–V = –2.5V
S
+V = 2.5V
S
–V = –2.5V
S
V
= 0V
V
= 0V
OCM
IN
IN
OCM
IN
IN
+V = ±50mV
+V = ±50mV
±
±
–V
C
=
50mV
= 0pF
–V
=
50mV
LOAD
0V
–60
–80
∆V
∆V
C
C
= 10000pF
= 1000pF
OUTCM
LOAD
LOAD
OUTDIFF
–100
1992 G52
1992 G53
1
10
100
1k
10k 100k
1M
1µs/DIV
10µs/DIV
FREQUENCY (Hz)
1992 G54
1992f
13
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-1 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
1000
100
10
C
C
= 10000pF
= 1000pF
LOAD
LOAD
2.5V
2.5V
+V = 5V
S
+V = 5V
–V = 0V
S
S
–V = 0V
V
= 2.5V
S
OCM
OCM
+V = 0V TO 200mV
V
= 2.5V
IN
–V = 100mV
+V = 0V TO 200mV
IN
IN
–V = 100mV
C
= 0pF
IN
LOAD
1992 G56
1992 G55
10µs/DIV
1µs/DIV
10
100
1000
10000
FREQUENCY (Hz)
1922 G57
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–50
–60
–70
–80
–90
–100
500kHz MEASUREMENT BANDWIDTH
500kHz MEASUREMENT BANDWIDTH
+V = 5V
S
+V = 5V
S
–V = –5V
S
–50
–60
–V = –5V
S
V
= 0V
OCM
V
OCM
= 0V
V
= 10V
P-PDIFF
OUT
50kHz
V
= 5V
OUT
P-PDIFF
20kHz
–70
V
V
= 1V
OUT
OUT
P-PDIFF
P-PDIFF
10kHz
5kHz
–80
= 2V
–90
2kHz
1kHz
–100
100
1k
10k
50k
0.1
1
10 20
FREQUENCY (Hz)
INPUT SIGNAL AMPLITUDE (V
)
P-PDIFF
1992 G59
1992 G58
1992f
14
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-2 only.
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response
vs Frequency
18
12
6
18
12
6
0
–20
0
–6
0
–6
–40
–60
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–12
–18
–24
–30
–36
–42
–48
–54
–60
–66
–80
C
=
LOAD
–100
–120
–140
–160
–180
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
= 10pF
= 10pF
10
100
1000
10000
10
100
1000
10000
10
100
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
1992 G60
1992 G61
1992 G62
Differential Gain Error vs
Temperature
VOCM Gain vs Frequency,
VS = ±2.5V
0.05
0.04
5
0
C
= 10pF TO 10000pF
LOAD
0.03
–5
0.02
0.01
–10
–15
–20
–25
–30
0
–0.01
–0.02
–0.03
–0.04
–0.05
–50
0
25
50
75 100 125
–25
10
100
1000
10000
TEMPERATURE (°C)
FREQUENCY (kHz)
1992 G64
1992 G63
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
Differential Input Offset Voltage
vs Input Common Mode Voltage
(Note 7)
2.0
2.0
1.5
2.0
1.5
+V = 2.7V
S
+V = 5V
S
+V = 5V
S
–V = 0V
S
–V = 0V
S
–V = –5V
S
1.5
1.0
V
= 1.35V
V
OCM
= 2.5V
V
OCM
= 0V
OCM
1.0
1.0
–40°C
25°C
–40°C
25°C
–40°C
25°C
0.5
0.5
0.5
85°C
0
0
0
85°C
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
125°C
125°C
125°C
85°C
1.2 1.5
1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
0
0.3 0.6 0.9
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1992 G66
–5 –4 –3 –2 –1
0
1
2
3
4
5
COMMON MODE VOLTAGE (V)
1992 G65
1992 G67
1992f
15
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-2 only.
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
100
90
80
70
60
50
40
30
20
10
0
+V = 2.5V
S
–V = –2.5V
S
+V = 2.5V
S
–V = –2.5V
S
V
= 0V
V
= 0V
OCM
IN
IN
OCM
IN
IN
+V = ±750mV
+V = ±750mV
±
±
–V
C
=
750mV
= 0pF
–V
=
750mV
LOAD
0V
0V
∆V
∆V
C
C
= 10000pF
= 1000pF
AMPCM
LOAD
LOAD
AMPDIFF
1992 G68
1992 G69
2µs/DIV
100
1k
10k
100k
1M
20µs/DIV
FREQUENCY (Hz)
1992 G70
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
90
+V = 5V
+V = 5V
S
–V = 0V
S
S
–V
+V
S
S
–V = 0V
S
OCM
V
= 2.5V
V
= 2.5V
OCM
IN
80
+V = 0V TO 2V
+V = 0V TO 2V
IN
–V = 1V
–V = 1V
IN
IN
70
C
= 0pF
LOAD
60
50
2.5V
2.5V
40
30
20
10
0
C
C
= 10000pF
= 1000pF
∆V
S
AMPDIFF
LOAD
LOAD
∆V
1992 G71
1992 G72
2µs/DIV
20µs/DIV
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
1992 G73
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Output Balance vs Frequency
0
+V = 2.5V
+V = 2.5V
S
–V = –2.5V
S
S
–V = –2.5V
S
OCM
V
= 0V
V
= 0V
OCM
IN
IN
–20
+V = ±25mV
+V = ±25mV
IN
±
±
–V
C
=
25mV
= 0pF
–V
=
25mV
IN
LOAD
–40
–60
0V
0V
–80
C
LOAD
C
LOAD
= 10000pF
= 1000pF
∆V
OUTCM
∆V
OUTDIFF
–100
1992 G74
1992 G75
1
10
100
1k
10k 100k
1M
2µs/DIV
20µs/DIV
FREQUENCY (Hz)
1992 G76
1992f
16
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-2 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
1000
100
10
C
C
= 10000pF
= 1000pF
LOAD
LOAD
2.5V
2.5V
+V = 5V
S
–V = 0V
S
+V = 5V
S
–V = 0V
S
V
= 2.5V
OCM
V
= 2.5V
+V = 0V TO 100mV
IN
OCM
+V = 0V TO 100mV
IN
–V = 50mV
IN
–V = 50mV
IN
C
LOAD
= 0pF
1992 G77
1992 G78
2µs/DIV
20µs/DIV
10
100
1000
10000
FREQUENCY (Hz)
1922 G79
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–50
–60
–70
–80
–90
–100
500kHz MEASUREMENT BANDWIDTH
+V = 5V
S
–50
–60
–V = –5V
S
OCM
V
= 0V
50kHz
20kHz
V
= 1V
OUT
P-PDIFF
–70
10kHz
5kHz
V
= 2V
OUT
P-PDIFF
–80
V
OUT
= 5V
P-PDIFF
2kHz
1kHz
–90
V
= 10V
P-PDIFF
OUT
–100
100
1k
FREQUENCY (Hz)
10k
50k
0.1
1
10
INPUT SIGNAL AMPLITUDE (V
)
P-PDIFF
1992 G81
1992 G80
1992f
17
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-5 only.
Differential Phase Response vs
Frequency
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
30
24
18
12
6
30
24
18
12
6
0
–20
–40
0
–6
–60
0
–6
–80
–12
–18
–24
–30
–36
–42
–48
–54
–60
–12
–18
–24
–30
–36
–42
–48
–54
–60
C
=
10pF
50pF
LOAD
–100
–120
–140
–160
–180
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
100pF
500pF
1000pF
5000pF
10000pF
= 10pF
= 10pF
10
100
1000
10000
10
100
1000
10
100
1000
10000
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
1992 G83
1992 G82
1992 G84
Differential Gain Error vs
Temperature
VOCM Gain vs Frequency
0.050
0.025
5
0
C
= 10pF TO 10000pF
LOAD
0
–5
–0.025
–0.050
–0.075
–0.100
–0.125
–01.50
–10
–15
–20
–25
–30
–50
0
25
50
75 100 125
10
100
1000
10000
–25
TEMPERATURE (°C)
FREQUENCY (kHz)
1992 G86
1992 G85
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
1.5
2.0
1.5
2.0
1.5
+V = 2.7V
S
+V = 5V
S
+V = 5V
S
–V = 0V
S
–V = 0V
S
–V = –5V
S
V
= 1.35V
V
OCM
= 2.5V
V
= 0V
OCM
OCM
1.0
1.0
1.0
–40°C
0.5
0.5
0.5
–40°C
–40°C
0
0
0
125°C
85°C
125°C
25°C
25°C
125°C
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
25°C
85°C
–0.5
–1.0
–1.5
–2.0
85°C
1.0
0
0.5
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
0.6
0
0.3
0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
1922 G87
–3
–5 –4
–2 –1
0
1
2
3
4
5
COMMON MODE VOLTAGE (V)
1922 G88
1922 G89
1992f
18
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-5 only.
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
100
90
80
70
60
50
40
30
20
10
0
+V = 2.5V
+V = 2.5V
S
S
–V = –2.5V
–V = –2.5V
S
S
OCM
V = 0V
V
= 0V
OCM
+V = ± 300mV
+V = ± 300mV
IN
–V =
IN
IN
±
±
300mV
–V
C
=
300mV
= 0pF
IN
LOAD
0V
0V
C
C
= 10000pF
= 1000pF
∆V
LOAD
LOAD
AMPCM
∆V
AMPDIFF
1992 G91
1992 G90
20µs/DIV
100
1k
10k
100k
1M
2µs/DIV
FREQUENCY (Hz)
1992 G92
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
90
C
C
= 10000pF
= 1000pF
LOAD
LOAD
80
70
+V
S
60
50
–V
S
2.5V
2.5V
40
30
20
10
0
+V = 5V
S
+V = 5V
S
–V = 0V
S
OCM
–V = 0V
S
OCM
V
= 2.5V
V
= 2.5V
+V = 0V TO 800mV
IN
∆V
+V = 0V TO 800mV
IN
S
–V = 400mV
IN
∆V
–V = 400mV
IN
AMPDIFF
C
= 0pF
LOAD
1992 G94
1992 G93
20µs/DIV
10
100
1k
10k
100k
1M
2µs/DIV
FREQUENCY (Hz)
1992 G95
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Output Balance vs Frequency
0
–20
–40
–60
–80
+V = 2.5V
+V = 2.5V
S
–V = –2.5V
S
S
–V = –2.5V
S
OCM
V
= 0V
V
IN
–V
= 0V
OCM
+V = ±10mV
+V = ±10mV
IN
IN
LOAD
±
±
–V
=
10mV
= 0pF
=
10mV
IN
C
0V
0V
∆V
C
LOAD
C
LOAD
= 10000pF
= 1000pF
OUTCM
∆V
OUTDIFF
–100
1992 G96
1992 G97
1
10
100
1k
10k 100k
1M
5µs/DIV
50µs/DIV
FREQUENCY (Hz)
1992 G98
1992f
19
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-5 only.
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
Single-Ended Input Small-Signal
Step Response
1000
100
10
C
LOAD
C
LOAD
= 10000pF
= 1000pF
2.5V
2.5V
+V = 5V
S
–V = 0V
S
+V = 5V
S
V
= 2.5V
–V = 0V
S
OCM
+V = 0V TO 40mV
IN
V
= 2.5V
OCM
–V = 20mV
IN
C
+V = 0V TO 40mV
IN
= 0pF
–V = 20mV
IN
LOAD
1992 G99
1992 G100
5µs/DIV
10
100
1000
10000
50µs/DIV
FREQUENCY (Hz)
1922 G101
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–50
–60
–70
–80
–90
–100
500kHz MEASUREMENT BANDWIDTH
500kHz MEASUREMENT BANDWIDTH
+V = 5V
+V = 5V
S
S
–50 –V = –5V
–V = –5V
S
S
OCM
V
= 0V
V
OCM
= 0V
50kHz
–60
–70
V
= 1V
= 2V
OUT
P-PDIFF
20kHz
10kHz
V
OUT
P-PDIFF
V
V
= 5V
P-PDIFF
OUT
5kHz
2kHz
–80
= 10V
P-PDIFF
OUT
–90
1kHz
–100
100
1k
FREQUENCY (Hz)
10k
50k
0.1
1
5
INPUT SIGNAL AMPLITUDE (V
)
P-PDIFF
1992 G103
1992 G102
1992f
20
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Differential Input Differential
Gain vs Frequency, VS = ±2.5V
Single-Ended Input Differential
Gain vs Frequency, VS = ±2.5V
Differential Phase Response vs
Frequency
40
30
40
30
0
–20
20
20
–40
10
10
–60
0
0
–80
–10
–20
–30
–40
–50
–60
–10
–20
–30
–40
–50
–60
C
=
10pF
50pF
100pF
500pF
1000pF
5000pF
10000pF
LOAD
–100
–120
–140
–160
–180
C
C
C
C
C
C
C
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
= 10000pF
= 5000pF
= 1000pF
= 500pF
= 100pF
= 50pF
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
= 10pF
= 10pF
10
100
1000
10
100
1000
10000
10
100
1000
10000
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
1992 G104
1992 G105
1992 G106
Differential Gain Error vs
Temperature
VOCM Gain vs Frequency
0.050
0.025
5
0
C
= 10pF TO 10000pF
LOAD
0
–0.025
–0.050
–0.075
–0.100
–0.125
–0.150
–0.175
–0.200
–5
–10
–15
–20
–25
–30
–50
0
25
50
75 100 125
–25
10
100
1000
10000
TEMPERATURE (°C)
FREQUENCY (kHz)
1992 G107
1992 G108
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
Differential Input Offset Voltage
vs Input Common Mode Voltage
2.0
1.5
2.0
1.5
2.0
1.5
+V = 2.7V
S
+V = 5V
S
+V = 5V
S
–V = 0V
S
–V = 0V
S
–V = –5V
S
V
= 1.35V
V
= 2.5V
V
= 0V
OCM
OCM
OCM
1.0
1.0
1.0
0.5
0.5
0.5
–40°C
–40°C
–40°C
0
0
0
125°C
125°C
85°C
25°C
125°C
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
–1.5
–2.0
25°C
85°C
25°C
85°C
0.6
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
COMMON MODE VOLTAGE (V)
1922 G110
–3
–5 –4
–2 –1
0
0.3
0.9 1.2 1.5 1.8 2.1 2.4 2.7
COMMON MODE VOLTAGE (V)
0
1
2
3
4
5
COMMON MODE VOLTAGE (V)
1922 G109
1922 G111
1992f
21
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Differential Input Large-Signal
Step Response
Differential Input Large-Signal
Step Response
Common Mode Rejection Ratio
vs Frequency (Note 7)
100
90
80
70
60
50
40
30
20
10
0
+V = 2.5V
S
–V = –2.5V
S
+V = 2.5V
S
–V = –2.5V
S
V
IN
–V
= 0V
V
= 0V
OCM
OCM
+V = ±150mV
IN
+V = ±150mV
IN
±
±
=
150mV
–V
C
=
150mV
= 0pF
IN
LOAD
0V
0V
∆V
AMPCM
C
LOAD
C
LOAD
= 10000pF
= 1000pF
∆V
AMPDIFF
1992 G113
1992 G112
100
1k
10k
100k
1M
20µs/DIV
2µs/DIV
FREQUENCY (Hz)
1992 G114
Single-Ended Input Large-Signal
Step Response
Single-Ended Input Large-Signal
Step Response
Power Supply Rejection Ratio
vs Frequency (Note 7)
100
90
C
C
= 10000pF
= 1000pF
LOAD
LOAD
80
+V
S
70
–V
S
60
50
2.5V
2.5V
40
30
20
10
0
+V = 5V
S
–V = 0V
S
OCM
+V = 5V
S
V
= 2.5V
–V = 0V
S
OCM
+V = 0V TO 400mV
IN
V
= 2.5V
–V = 200mV
IN
∆V
+V = 0V TO 400mV
IN
S
C
= 0pF
LOAD
–V = 200mV
IN
∆V
AMPDIFF
1992 G115
1992 G116
2µs/DIV
10
100
1k
10k
100k
1M
20µs/DIV
FREQUENCY (Hz)
1992 G117
Differential Input Small-Signal
Step Response
Differential Input Small-Signal
Step Response
Output Balance vs Frequency
0
–20
–40
–60
–80
–100
+V = 2.5V
+V = 2.5V
S
–V = –2.5V
S
S
–V = –2.5V
S
OCM
V
= 0V
V
= 0V
OCM
IN
IN
+V = ±5mV
+V = ±5mV
IN
±
±
–V
C
=
5mV
–V
=
5mV
IN
LOAD
= 0pF
0V
0V
∆V
C
C
= 10000pF
= 1000pF
OUTCM
LOAD
LOAD
∆V
OUTDIFF
–120
1992 G118
1992 G119
1
10
100
1k
10k 100k
1M
10µs/DIV
100µs/DIV
FREQUENCY (Hz)
1992 G120
1992f
22
LTC1992 Family
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Applicable to the LTC1992-10 only.
Single-Ended Input Small-Signal
Step Response
Single-Ended Input Small-Signal
Step Response
Differential Noise Voltage Density
vs Frequency
1000
100
10
C
C
= 10000pF
= 1000pF
LOAD
LOAD
2.5V
2.5V
+V = 5V
S
+V = 5V
S
–V = 0V
S
–V = 0V
S
V
= 2.5V
OCM
V
= 2.5V
+V = 0V TO 20mV
IN
OCM
+V = 0V TO 20mV
IN
–V = 10mV
IN
C
–V = 10mV
IN
= 0pF
LOAD
1992 G121
1992 G122
10µs/DIV
100µs/DIV
10
100
1000
10000
FREQUENCY (Hz)
1922 G123
THD + Noise vs Frequency
THD + Noise vs Amplitude
–40
–40
–50
–60
–70
–80
–90
–100
500kHz MEASUREMENT BANDWIDTH
+V = 5V
S
50kHz
20kHz
–50 –V = –5V
S
OCM
V
= 0V
–60
–70
V
= 1V
= 2V
= 5V
OUT
P-PDIFF
P-PDIFF
P-PDIFF
V
OUT
10kHz
5kHz
V
OUT
–80
2kHz
1kHz
–90
–100
100
1k
10k
50k
0.1
1
2
FREQUENCY (Hz)
INPUT SIGNAL AMPLITUDE (V
)
P-PDIFF
1992 G125
1992 G124
1992f
23
LTC1992 Family
U
U
U
PI FU CTIO S
+VS, –VS (Pins 3, 6): The +VS and –VS power supply pins
should be bypassed with 0.1µF capacitors to an adequate
analog ground or ground plane. The bypass capacitors
shouldbelocatedascloselyaspossibletothesupplypins.
–IN, +IN (Pins 1, 8): Inverting and Noninverting Inputs of
the Amplifier. For the LTC1992 part, these pins are con-
nected directly to the amplifier’s P-channel MOSFET input
devices. The fixed gain LTC1992-X parts have precision,
on-chip gain setting resistors. The input resistors are
nominally 30k for the LTC1992-1, LTC1992-2 and
LTC1992-5 parts. The input resistors are nominally 15k
for the LTC1992-10 part.
+OUT, –OUT (Pins 4, 5): The Positive and Negative
Outputs of the Amplifier. These rail-to-rail outputs are
designed to drive capacitive loads as high as 10,000pF.
V
MID (Pin7):Mid-SupplyReference.Thispinisconnected
V
OCM (Pin 2): Output Common Mode Voltage Set Pin. The
to an on-chip resistive voltage divider to provide a mid-
supply reference. This provides a convenient way to set
the output common mode level at half-supply. If used for
this purpose, Pin 2 will be shorted to Pin 7, Pin 7 should
be bypassed with a 0.1µF capacitor to ground. If this
reference voltage is not used, leave the pin floating.
voltage on this pin sets the output signal’s common mode
voltage level. The output common mode level is set
independent of the input common mode level. This is a
high impedance input and must be connected to a known
and controlled voltage. It must never be left floating.
W
BLOCK DIAGRA S
(1992)
+V
S
3
+V
S
–IN
MID
1
7
2
+
–
V
+
+OUT
4
∑
∑
–V
S
200k
+
30k
30k
V
200k
–
+
–
+
A1
A2
V
V
OCM
+IN
+
+V
–OUT
5
1992 BD
S
–
8
–V
S
6
–V
S
1992f
24
LTC1992 Family
W
BLOCK DIAGRA S
(1992-X)
+V
S
3
+V
S
R
R
FB
IN
–IN
1
7
200k
200k
–V
S
4
5
+OUT
–
+
+
–
V
MID
+IN
–OUT
+V
S
R
R
FB
IN
8
PART
R
R
FB
IN
LTC1992-1 30k 30k
LTC1992-2 30k 60k
LTC1992-5 30k 150k
LTC1992-10 15k 150k
–V
S
6
–V
2
1992-X BD
V
S
OCM
W U U
U
APPLICATIO S I FOR ATIO
Theory of Operation
monmodevoltageandallowstheoutputsignal’scommon
mode voltage to be set completely independent of the
input signal’s common mode voltage. Uncoupling the
input and output common mode voltages makes signal
level shifting easy.
The LTC1992 family consists of five fully differential, low
power amplifiers. The LTC1992 is an unconstrained fully
differential amplifier. The LTC1992-1, LTC1992-2,
LTC1992-5 and LTC1992-10 are fixed gain blocks (with
gainsof1,2,5and10respectively)featuringprecisionon-
chip resistors for accurate and ultra stable gain.
Forabetterunderstandingoftheoperationofafullydiffer-
ential amplifier, refer to Figure 2. Here, the LTC1992 func-
tionalblockdiagramaddsexternalresistorstorealizeabasic
gainblock.NotethattheLTC1992functionalblockdiagram
is not an exact replica of the LTC1992 circuitry. However,
the Block Diagram is correct and is a very good tool for
understanding the operation of fully differential amplifier
circuits.Basicopampfundamentalstogetherwiththisblock
diagram provide all of the tools needed for understanding
fully differential amplifier circuit applications.
In many ways, a fully differential amplifier functions much
like the familiar, ubiquitous op amp. However, there are
several key areas where the two differ. Referring to Fig-
ure 1, an op amp has a differential input, a high open-loop
gain and utilizes negative feedback (through resistors) to
set the closed-loop gain and thus control the amplifier’s
gain with great precision. A fully differential amplifier has
all of these features plus an additional input and a comple-
mentary output. The complementary output reacts to the
input signal in the same manner as the other output, but
in the opposite direction. Two outputs changing in an
equal but opposite manner require a common reference
point (i.e., opposite relative to what?). The additional
input, the VOCM pin, sets this reference point. The voltage
on the VOCM input directly sets the output signal’s com-
The LTC1992 Block Diagram has two op amps, two
summing blocks (pay close attention the signs) and four
resistors. Two resistors, RMID1 and RMID2, connect di-
rectly to the VMID pin and simply provide a convenient
midsupply reference. Its use is optional and it is not
involved in the operation of the LTC1992’s amplifier. The
LTC1992functionsthroughtheuseoftwoservonetworks
1992f
25
LTC1992 Family
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APPLICATIO S I FOR ATIO
Op Amp
Fully Differential Amplifier
–IN
–IN
+OUT
+
–
–
LTC1992
LTC1992
V
OUT
OCM
+IN
A
A
O
O
+IN
–OUT
+
+
–
• DIFFERENTIAL INPUT
• HIGH OPEN-LOOP GAIN
• SINGLE-ENDED OUTPUT
• DIFFERENTIAL INPUT
• HIGH OPEN-LOOP GAIN
• DIFFERENTIAL OUTPUT
OCM
COMMON MODE LEVEL
• V
INPUT SETS OUTPUT
Op Amp with Negative Feedback
Fully Differential Amplifier with Negative Feedback
R
FB
R
FB
R
IN
R
R
IN
V
IN
–V
+V
+V
V
V
–
+
–
+
IN
OUT
OCM
+
LTC1992
V
OUT
LTC1992
IN
–
–V
OUT
IN
OCM
R
R
FB
GAIN = –
IN
R
R
FB
GAIN = –
V
OCM
R
FB
IN
1992 F01
Figure 1. Comparison of an Op Amp and a Fully Differential Amplifier
R
FB
+V
S
3
LTC1992
R
IN
INM
–IN
MID
+V
1
7
2
IN
+
S
V
P
+
+OUT
+V
4
R
OUT
∑
MID1
200k
+
R
CMP
30k
V
R
MID2
200k
–
+
–
+
A1
A2
–
R
CMM
30k
V
V
OCM
+IN
+
–OUT
–V
5
∑
OUT
–
S
M
R
IN
INP
–V
8
IN
6
–V
S
R
FB
1992 F02
Figure 2. LTC1992 Functional Block Diagram with External Gain Setting Resistors
1992f
26
LTC1992 Family
W U U
APPLICATIO S I FOR ATIO
U
each employing negative feedback and using an op amp’s
differential input to create the servo’s summing junction.
out of the specified areas of operation (e.g., inputs taken
beyond the common mode range specifications, outputs
hitting the supply rails or input signals varying faster than
the part can track), the circuit will not function properly.
Oneservocontrolsthesignalgainpath.Thedifferentialinput
of op amp A1 creates the summing junction of this servo.
Any voltage present at the input of A1 is amplified (by the
opamp’slargeopen-loopgain),senttothesummingblocks
and then onto the outputs. Taking note of the signs on the
summing blocks, op amp A1’s output moves +OUT and
–OUTinoppositedirections.Applyingavoltagestepatthe
INMnodeincreasesthe+OUTvoltagewhilethe–OUTvolt-
agedecreases.TheRFB resistorsconnecttheoutputstothe
appropriateinputsestablishingnegativefeedbackandclos-
ingtheservo’sloop.Anyservoloopalwaysattemptstodrive
its error voltage to zero. In this servo, the error voltage is
the voltage between the INM and INP nodes, thus A1 will
force the voltages on the INP and INM nodes to be equal
(within the part’s DC offset, open loop gain and bandwidth
limits). The “virtual short” between the two inputs is con-
ceptually the same as that for op amps and is critical to un-
derstanding fully differential amplifier applications.
Fully Differential Amplifier Signal Conventions
Fully differential amplifiers have a multitude of signals and
signal ranges to consider. To maintain proper operation
with conventional op amps, the op amp’s inputs and its
output must not hit the supply rails and the input signal’s
common mode level must also be within the part’s speci-
fied limits. These considerations also apply to fully differ-
ential amplifiers, but here there is an additional output to
consider and common mode level shifting complicates
matters. Figure 3 provides a list of the many signals and
specifications as well as the naming convention. The
phrase“commonmode”appearsinmanyplacesandoften
leads to confusion. The fully differential amplifier’s ability
to uncouple input and output common mode levels yields
greatdesignflexibility,butalsocomplicatesmatterssome.
For simplicity, the equations in Figure 3 also assume an
ideal amplifier and perfect resistor matching. For a de-
tailedanalysis, consultthefullydifferentialamplifierappli-
cations circuit analysis section..
The other servo controls the output common mode level.
The differential input of op amp A2 creates the summing
junction of this servo. Similar to the signal gain servo
above, any voltage present at the input of A2 is amplified,
sent to the summing blocks and then onto the outputs.
However, in this case, both outputs move in the same
direction. TheresistorsRCMP andRCMM connectthe+OUT
and –OUT outputs to A2’s inverting input establishing
negative feedback and closing the servo’s loop. The mid-
point of resistors RCMP and RCMM derives the output’s
commonmodelevel(i.e.,itsaverage).Thismeasureofthe
output’s common mode level connects to A2’s inverting
input while A2’s noninverting input connects directly to
the VOCM pin. A2 forces the voltages on its inverting and
noninverting inputs to be equal. In other words, it forces
the output common mode voltage to be equal to the
voltage on the VOCM input pin.
Basic Applications Circuits
Most fully differential amplifier applications circuits em-
ploy symmetrical feedback networks and are familiar
territory for op amp users. Symmetrical feedback net-
works require that the –VIN/+VOUT network is a mirror
image duplicate of the +VIN/–VOUT network. Each of these
half circuits is basically just a standard inverting gain op
amp circuit. Figure 4 shows three basic inverting gain op
amp circuits and their corresponding fully differential
amplifier cousins. The vast majority of fully differential
amplifier circuits derive from old tried and true inverting
op amp circuits. To create a fully differential amplifier
circuit from an inverting op amp circuit, first simply
transfer the op amp’s VIN/VOUT network to the fully differ-
ential amplifier’s –VIN/+VOUT nodes. Then, take a mirror
image duplicate of the network and apply it to the fully
differential amplifier’s +VIN/–VOUT nodes. Op amp users
can comfortably transfer any inverting op amp circuit to a
For any fully differential amplifier application to function
properlyboththesignalgainservoandthecommonmode
level servo must be satisfied. When analyzing an applica-
tions circuit, the INP node voltage must equal the INM
node voltage and the output common mode voltage must
equal the VOCM voltage. If either of these servos is taken
fully differential amplifier in this manner.
1992f
27
LTC1992 Family
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APPLICATIO S I FOR ATIO
R
FB
R
IN
IN
A
B
INM
INP
2AV
–V
2BV
2BV
+
–
+V
–
P-P
P-P
P-P
IN
IN
OUT
–A
A
–B
B
V
V
INDIFF
OUTDIFF
4BV
LTC1992
V
OCM
V
OCM
V
INCM
V
OUTCM
4AV
P-PDIFF
P-PDIFF
R
+V
2AV
+
–V
P-P
OUT
–A
–B
R
FB
1992 F03
DIFFERENTIAL
INPUT VOLTAGE
DIFFERENTIAL
OUTPUT VOLTAGE
= V
INDIFF
= +V – –V
IN IN
= V
OUTDIFF
= +V
OUT
– –V
OUT
+V + –V
IN
+V
OUT
+ –V
2
INPUT COMMON
MODE VOLTAGE
IN
OUTPUT COMMON
MODE VOLTAGE
OUT
= V
INCM
=
= V =
OUTCM
2
R
R
1
2
FB
IN
+V
–V
=
=
+V – –V
IN
•
•
•
•
+ V
; V
; V
= 0V
= 0V
OUT
IN
IN
OCM
OCM
OSCM
(
(
)
)
R
R
1
2
FB
–V – +V
IN
+ V
OUT
OSCM
IN
R
FB
IN
V
V
V
V
= V •
INDIFF
R
OUTDIFF
= V – V
INP
AMPDIFF
INM
V
INP
+ V
INM
2
=
AMPCM
OUTCM
= V
OCM
∆V
AMPCM
CMRR =
; +V = –V
IN IN
∆V
AMPDIFF
∆V
OUTCM
OUTDIFF
OUTPUT BALANCE =
∆V
R
R
FB
IN
2
2
e
=
+ 1
WHERE: e
= OUTPUT REFERRED NOISE VOLTAGE DENSITY
NOUT
NIN
• √e
+ r
N
NOUT
(
)
NIN
e
= INPUT REFERRED NOISE VOLTAGE DENSITY
R
R
• R
FB
+ R
FB
IN
IN
r
N
≈ (0.13nV/√Hz)
(
)
(RESISTIVE NOISE IS ALREADY INCLUDED IN THE
SPECIFICATIONS FOR THE FIXED GAIN LTC1992-X PARTS)
R
R
FB
IN
V
V
= V
OSDIFFIN
•
+ 1
OSDIFFOUT
(
)
= V
– V
OCM
OSCM
OUTCM
Figure 3. Fully Differential Amplifier Signal Conventions (Ideal Amplifier and Perfect Resistor Matching is Assumed)
Single-Ended to Differential Conversion
for the signal path only affects the polarity of the differ-
ential output signal.
One of the most important applications of fully differen-
tial amplifiers is single-ended signaling to differential
signalingconversion.Manysystemshaveasingle-ended
signal that must connect to an ADC with a differential
input. The ADC could be run in a single-ended manner,
but performance usually degrades. Fortunately, all of
basic applications circuits shown in Figure 4, as well as
all of the fixed gain LTC1992-X parts, are equally suitable
for both differential and single-ended input signals. For
single-ended input signals, connect one of the inputs to
a reference voltage (e.g., ground or midsupply) and
connecttheothertothesignalpath.Therearenotradeoffs
here as the part’s performance is the same with single-
ended or differential input signals. Which input is used
Signal Level Shifting
Anotherimportantapplicationoffullydifferentialamplifier
issignallevelshifting. Single-endedtodifferentialconver-
sion accompanied by a signal level shift is very common-
place when driving ADCs. As noted in the theory of
operation section, fully differential amplifiers have a com-
monmodelevelservothatdeterminestheoutputcommon
mode level independent of the input common mode level.
To set the output common mode level, simply apply the
desiredvoltagetotheVOCM inputpin.Thevoltagerangeon
the VOCM pin is from (–VS + 0.5V) to (+VS – 1.3V).
1992f
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LTC1992 Family
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APPLICATIO S I FOR ATIO
U
Gain Block
R
R
FB
FB
R
R
R
IN
IN
IN
V
–V
+V
+
+V
–
+
–
IN
IN
IN
OUT
V
LTC1992
V
OUT
OCM
+
–
–V
OUT
R
R
FB
R
R
FB
GAIN =
IN
AC Coupled Gain Block
R
FB
FB
C
C
C
IN
IN
R
R
IN
IN
V
–V
IN
+
+V
OUT
IN
–
+
–
V
LTC1992
V
OUT
OCM
IN
R
IN
+V
IN
+
–
–V
OUT
S
H
= H •
O
(S)
S + ω
R
FB
P
R
R
1
• C
FB
IN
H
O
=
; ω
P
=
R
IN
IN
Single Pole Lowpass Filter
C
C
R
R
FB
FB
R
R
IN
IN
IN
V
–V
IN
+
+V
–V
–
+
–
IN
OUT
OUT
V
LTC1992
V
OUT
OCM
R
+V
IN
+
–
ω
S + ω
R
P
FB
H
= H
R
•
O
(S)
P
C
1
FB
FB
WHERE H
=
; ω
P
=
O
R
R
• C
IN
3-Pole Lowpass Filter
R2
C1
R2
C1
R1
R3
R1
R1
R3
C2
R4
R4
V
–V
IN
+
+V
–V
–
+
–
IN
OUT
OUT
R4
C2
C3
2
V
LTC1992
V
OUT
OCM
2
C3
R3
+V
+
–
IN
C1
2
ω
O
O
Q
ω
S + ω
P
H
= H
O
(S)
ω
(
)(
)
2
2
P
ω
S
+ S
+
O
R2
1992 F04
1
1
R2
R1
WHERE H
=
; ω
=
; ω =
O
O
P
R4C3
R1 • √R2R3
R1 R2 + R1 R2 + R2 R3
R2R3C1C2
C2
C1
Q =
•
Figure 4. Basic Fully Differential Amplifier Application Circuits (Note: Single-Ended to Differential Conversion is
Easily Accomplished by Connecting One of the Input Nodes, +VIN or –VIN, to a DC Reference Level (e.g.,
Ground))
1992f
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LTC1992 Family
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APPLICATIO S I FOR ATIO
The VOCM input pin has a very high input impedance and
is easily driven by even the weakest of sources. Many
ADCs provide a voltage reference output that defines
either its common mode level or its full-scale level. Apply
the ADC’s reference potential either directly to the VOCM
pin or through a resistive voltage divider depending on the
reference voltage’s definition. When controlling the VOCM
pin by a high impedance source, connect a bypass capaci-
tor(1000pFto0.1µF)fromtheVOCM pintogroundtolower
the high frequency impedance and limit external noise
coupling. Other applications will want the output biased at
a midpoint of the power supplies for maximum output
voltage swing. For these applications, the LTC1992 pro-
vides a midsupply potential at the VMID pin. The VMID pin
connects to a simple resistive voltage divider with two
200k resistors connected between the supply pins. To use
this feature, connect the VMID pin to the VOCM pin and
bypass this node with a capacitor.
dominates low frequency CMRR performance. The speci-
fications for the fixed gain LTC1992-X parts include the
on-chip resistor matching effects. Also, note that an input
common mode signal appears as a differential output
signal reduced by the CMRR. As with op amps, at higher
frequencies the CMRR degrades. Refer to the Typical
Performance plots for the details of the CMRR perfor-
mance over frequency.
At low frequencies, the output balance specification is
determined by the matching of the on-chip RCMM and
R
CMP resistors. At higher frequencies, the output balance
degrades. Refer to the typical performance plots for the
details of the output balance performance over frequency.
Input Impedance
The input impedance for a fully differential amplifier appli-
cation circuit is similar to that of a standard op amp
inverting amplifier. One major difference is that the input
impedance is different for differential input signals and
single-ended signals. Referring to Figure 3, for differential
input signals the input impedance is expressed by the
following expression:
One undesired effect of utilizing the level shifting function
is an increase in the differential output offset voltage due
to gain setting resistor mismatch. The offset is approxi-
mately the amount of level shift (VOUTCM – VINCM) multi-
plied by the amount of resistor mismatch. For example, a
2V level shift with 0.1% resistors will give around 2mV of
output offset (2 • 0.1% = 2mV). The exact amount of offset
is dependent on the application’s gain and the resistor
mismatch.Foradetaildescription,consulttheFullyDiffer-
ential Amplifier Applications Circuit Analysis section.
RINDIFF = 2 • RIN
For single-ended signals, the input impedance is ex-
pressed by the following expression:
RIN
RFB
RINS-E
=
1–
CMRR and Output Balance
2 • R +R
(
)
IN
FB
Onecommonmisconceptionoffullydifferentialamplifiers
is that the common mode level servo guarantees an
infinite common mode rejection ratio (CMRR). This is not
true. The common mode level servo does, however, force
the two outputs to be truly complementary (i.e., exactly
opposite or 180 degrees out of phase). Output balance is
a measure of how complementary the two outputs are.
The input impedance for single-ended signals is slightly
higher than the RIN value since some of the input signal is
fed back and appears as the amplifier’s input common
mode level. This small amount of positive feedback in-
creases the input impedance.
Driving Capacitive Loads
At low frequencies, CMRR is primarily determined by the
matching of the gain setting resistors. Like any op amp,
the LTC1992 does not have infinite CMRR, however resis-
tor mismatching of only 0.018%, halves the circuit’s
CMRR. Standard 1% tolerance resistors yield a CMRR of
about 40dB. For most applications, resistor matching
The LTC1992 family of parts is stable for all capacitive
loadsuptoatleast10,000pF.Whilestabilityisguaranteed,
the part’s performance is not unaffected by capacitive
loading. Large capacitive loads increase output step re-
sponse ringing and settling time, decrease the bandwidth
1992f
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LTC1992 Family
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APPLICATIO S I FOR ATIO
U
and increase the frequency response peaking. Refer to the
Typical Performance plots for small-signal step response,
large-signal step response and gain over frequency to
appraise the effects of capacitive loading. While the con-
sequences are minor in most instances, consider these
effects when designing application circuits with large
capacitive loads.
random. Once the input returns to the specified input
common mode range, there is a small recovery time then
normal operation proceeds.
TheLTC1992’sinputsignalcommonmoderange(VINCMR
)
is from (–VS – 0.1V) to (+VS – 1.3V). This specification
applies to the voltage at the amplifier’s input, the INP and
INMnodesofFigure2.Thespecificationsforthefixedgain
LTC1992-X parts reflect a higher maximum limit as this
specification is for the entire gain block and references the
signal at the input resistors. Differential input signals and
single-ended signals require a slightly different set of
formulae. Differential signals separate very nicely into
common mode and differential components while single
endedsignalsdonot. RefertoFigure5fortheformulaefor
calculatingtheavailablesignalrange. Additionally, Table1
lists some common configurations and their appropriate
signal levels.
Input Signal Amplitude Considerations
For application circuits to operate correctly, the amplifier
must be in its linear operating range. To be in the linear
operating range, the input signal’s common mode voltage
must be within the part’s specified limits and the rail-to-
rail outputs must stay within the supply voltage rails.
Additionally, the fixed gain LTC1992-X parts have input
protectiondiodesthatlimittheinputsignaltobewithinthe
supply voltage rails. The unconstrained LTC1992 uses
external resistors allowing the source signals to go be-
yond the supply voltage rails.
The LTC1992’s outputs allow rail-to-rail signal swings.
The output voltage on either output is a function of the
input signal’s amplitude, the gain configured and the
output signal’s common mode level set by the VOCM pin.
For maximum signal swing, the VOCM pin is set at the
midpoint of the supply voltages. For other applications,
such as an ADC driver, the required level must fall within
the VOCM range of (–VS + 0.5V) to (+VS – 1.3V). For single-
ended input signals, it is not always obvious which output
will clip first thus both outputs are calculated and the
minimum value determines the signal limit. Refer to
Figure 5 for the formulae and Table 1 for examples.
When taken outside of the linear operating range, the
circuit does not perform as expected, however nothing
extreme occurs. Outputs driven into the supply voltage
rails are simply clipped. There is no phase reversal or
oscillation. Once the outputs return to the linear operating
range, there is a small recovery time, then normal opera-
tion proceeds. When the input common mode voltage is
below the specified lower limit, on-chip protection diodes
conduct and clamp the signal. Once the signal returns to
thespecifiedoperatingrange, normaloperationproceeds.
If the input common mode voltage goes slightly above the
specified upper limit (by no more than about 500mV), the
amplifier’s open-loop gain reduces and DC offset and
closed-loop gain errors increase. Return the input back to
the specified range and normal performance commences.
If taken well above the upper limit, the amplifier’s input
stage is cut off. The gain servo is now open loop; however,
thecommonmodeservoisstillfunctional. Outputbalance
is maintained and the outputs go to opposite supply rails.
However, which output goes to which supply rail is
To ensure proper linear operation both the input common
mode level and the output signal level must be within the
specified limits. These same criteria are also present with
standardopamps. However, withafullydifferentialampli-
fier, it is a bit more complex and old familiar op amp
intuition often leads to the wrong result. This is especially
true for single-ended to differential conversion with level
shifting.Therequiredcalculationsareabittedious,butare
necessary to guarantee proper linear operation.
1992f
31
LTC1992 Family
W U U
U
APPLICATIO S I FOR ATIO
Differential Input Signals
R
FB
INM
NODE
R
IN
A
B
2AV
–V
2BV
2BV
+
–
+V
OUT
–
P-P
P-P
IN
–A
A
–B
B
V
V
INDIFF
OUTDIFF
4BV
LTC1992
V
V
OCM
V
INCM
V
OUTCM
OCM
4AV
P-PDIFF
P-PDIFF
R
IN
+V
2AV
P-P
+
–V
OUT
IN
P-P
–B
–A
INP
NODE
R
R
FB
IN
R
FB
G =
INPUT COMMON MODE LIMITS
A. CALCULATE V
INCM
MINIMUM AND MAXIMUM GIVEN R , R AND V
IN FB
OCM
1
V
= (+V – 1.3V) +
(+V – 1.3V – V )
OCM
INCM(MAX)
S
S
G
1
G
V
= (–V – 0.1V) +
(–V – 0.1V – V )
S OCM
INCM(MIN)
S
B. WITH A KNOWN V
, R , R AND V
, CALCULATE COMMON MODE
OR
INCM IN FB
OCM
VOLTAGE AT INP AND INM NODES (V
) AND CHECK THAT IT IS
1
INCM(AMP)
WITHIN THE SPECIFIED LIMITS.
V
+ V
INM
2
G
G + 1
INP
V
=
=
V
+
V
INCM(AMP)
INCM
OCM
G + 1
OUTPUT SIGNAL CLIPPING LIMIT
V (V
4
G
4
G
) = THE LESSER VALUE OF (+V – V
) OR (V – –V )
INDIFF(MAX) P-PDIFF
S
OCM OCM S
Single End Input Signals
R
FB
INM
NODE
R
R
IN
B
2BV
2BV
+
–
V
+V
OUT
–
P-P
INREF
–B
B
V
OUTDIFF
4BV
LTC1992
V
OCM
V
OCM
V
OUTCM
P-PDIFF
IN
A
V
+
2AV
P-P
–V
OUT
V
REF
INSIG
P-P
–B
–A
INP
NODE
R
R
FB
IN
R
FB
G =
INPUT COMMON MODE LIMITS (NOTE: FOR THE FIXED GAIN LTC1992-X PARTS, V
INREF
AND V
CANNOT EXCEED THE SUPPLIES)
INSIG
V
1
G
INREF
2
V
V
V
= 2 +V – 1.3V –
+
+
+V – 1.3V – V
S
INSIG(MAX)
S
OCM
(
)
)
(
(
)
)
V
INREF
2
1
G
= 2 –V – 0.1V –
–V – 0.1V – V
S
INSIG(MIN)
S
OCM
(
OR
1
= 2 (+V – –V ) – 1.2V +
(+V – –V ) – 1.2V
S S
INSIGP-P
S
S
(
)
(
)
G
OUTPUT SIGNAL CLIPPING LIMIT
2
G
2
G
V
= THE LESSER VALUE OF V
INREF
+
(+V – V
) OR V +
INREF
(V
OCM
– –V )
S
INSIG(MAX)
INSIG(MIN)
S
OCM
2
G
2
G
V
= THE GREATER VALUE OF V
INREF
+
(–V – V
S
) OR V
OCM INREF
+
(V – +V ) 1992 F05
OCM S
Figure 5. Input Signal Limitations
1992f
32
LTC1992 Family
W U U
APPLICATIO S I FOR ATIO
U
Table 1. Input Signal Limitations for Some Common Applications
Differential Input Signal, VOCM at Midsupply. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+V
–V
(V)
GAIN
(V/V)
V
V
V
V
(V
V
OUTDIFF(MAX)
S
S
OCM
INCM(MAX)
(V)
INCM(MIN)
(V)
INDIFF(MAX)
(V)
2.7
2.7
2.7
2.7
5
(V)
1.35
1.35
1.35
1.35
2.5
2.5
2.5
2.5
0
)
(V
P-PDIFF
)
P-PDIFF
0
1
2
1.450
1.425
1.410
1.405
4.900
4.300
3.940
3.820
7.400
5.550
4.440
4.070
–1.550
–0.825
–0.390
–0.245
–2.700
–1.400
–0.620
–0.360
5.40
5.40
0
2.70
1.08
0.54
5.40
5.40
5.40
0
5
0
10
1
0
10.00
5.00
10.00
10.00
10.00
10.00
20.00
20.00
20.00
20.00
5
0
2
5
0
5
2.00
5
0
10
1
1.00
5
–5
–5
–5
–5
–10.200
–7.650
–6.120
–5.610
20.00
10.00
4.00
5
2
0
5
5
0
5
10
0
2.00
Differential Input Signal, VOCM at Typical ADC Levels. (VINCM must be within the Min and Max table values and
VINDIFF must be less than the table value)
+V
–V
(V)
GAIN
(V/V)
V
(V)
V
V
V
(V
V
OUTDIFF(MAX)
S
S
OCM
INCM(MAX)
(V)
INCM(MIN)
(V)
INDIFF(MAX)
(V)
2.7
2.7
2.7
2.7
5
)
(V
P-PDIFF
)
P-PDIFF
0
1
2
1
1.800
1.600
1.480
1.440
5.400
4.550
4.040
3.870
5.400
4.550
4.040
3.870
–1.200
–0.650
–0.320
–0.210
–2.200
–1.150
–0.520
–0.310
4.00
4.00
0
1
2.00
0.80
0.40
8.00
4.00
1.60
0.80
4.00
4.00
4.00
8.00
8.00
8.00
8.00
0
5
1
0
10
1
1
0
2
5
0
2
2
5
0
5
2
5
0
10
1
2
5
–5
–5
–5
–5
2
–12.200
–8.650
–6.520
–5.810
12.00
6.00
2.40
1.20
12.00
12.00
12.00
12.00
5
2
2
5
5
2
5
10
2
1992f
33
LTC1992 Family
W U U
U
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications
Midsupply Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for both the input
common mode limits and the output clipping)
+V
–V
(V)
GAIN
(V/V)
V
V
V
V
V
V
OUTDIFF(MAX)
S
S
OCM
INREF
(V)
INSIG(MAX)
(V)
INSIG(MIN)
(V)
INSIGP-P(MAX)
(V)
2.7
2.7
2.7
2.7
5
(V)
1.35
1.35
1.35
1.35
2.5
2.5
2.5
2.5
0
(V AROUND V
P-P
)
(V
P-PDIFF
)
INREF
0
1
2
1.35
1.35
1.35
1.35
2.5
2.5
2.5
2.5
0
1.550
1.500
1.470
1.460
7.300
5.000
3.500
3.000
10.000
5.000
2.000
1.000
–1.350
0.000
0.810
1.080
–2.500
0.000
1.500
2.000
0.40
0.30
0.24
0.22
9.60
5.00
2.00
1.00
20.00
10.00
4.00
2.00
0.40
0
0.60
1.20
2.20
9.60
0
5
0
10
1
0
5
0
2
10.00
10.00
10.00
20.00
20.00
20.00
20.00
5
0
5
5
0
10
1
5
–5
–5
–5
–5
–10.000
–5.000
–2.000
–1.000
5
2
0
0
5
5
0
0
5
10
0
0
Midsupply Referenced Single-Ended Input Signal, VOCM at Typical ADC Levels. (The VINSIG Min and Max values listed account for both
the input common mode limits and the output clipping)
+V
–V
(V)
GAIN
(V/V)
V
(V)
V
V
V
V
V
OUTDIFF(MAX)
S
S
OCM
INREF
(V)
INSIG(MAX)
(V)
INSIG(MIN)
(V)
INSIGP-P(MAX)
(V)
2.7
2.7
2.7
2.7
5
(V AROUND V
P-P
)
(V
P-PDIFF
)
INREF
0
1
2
1
1.35
1.35
1.35
1.35
2.5
2.5
2.5
2.5
0
2.250
1.850
1.610
1.530
6.500
4.500
3.300
2.900
6.000
3.000
1.200
0.600
–0.650
0.350
1.80
1.00
0.52
0.36
8.00
4.00
1.60
0.80
12.00
6.00
2.40
1.20
1.80
0
1
2.00
2.60
3.60
8.00
8.00
8.00
8.00
0
5
1
0.950
0
10
1
1
1.150
0
2
–1.500
0.500
5
0
2
2
5
0
5
2
1.700
5
0
10
1
2
2.100
5
–5
–5
–5
–5
2
–6.000
–3.000
–1.200
–0.600
12.00
12.00
12.00
12.00
5
2
2
0
5
5
2
0
5
10
2
0
1992f
34
LTC1992 Family
W U U
APPLICATIO S I FOR ATIO
U
Table 1. Input Signal Limitations for Some Common Applications
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for
both the input common mode limits and the output clipping)
+V
–V
(V)
GAIN
(V/V)
V
V
V
V
V
V
OUTDIFF(MAX)
S
S
OCM
INREF
(V)
INSIG(MAX)
(V)
INSIG(MIN)
(V)
INSIGP-P(MAX)
(V)
2.7
2.7
2.7
2.7
5
(V)
1.35
1.35
1.35
1.35
2.5
(V AROUND V
P-P
)
(V
P-PDIFF
)
INREF
0
1
2
0
0
0
0
0
0
0
0
2.700
1.350
0.540
0.270
5.000
2.500
1.000
0.500
–2.700
–1.350
–0.540
–0.270
–5.000
–2.500
–1.000
–0.500
5.40
2.70
1.08
0.54
10.00
5.00
2.00
1.00
5.40
0
5.40
5.40
5.40
0
5
0
10
1
0
10.00
10.00
10.00
10.00
5
0
2
2.5
5
0
5
2.5
5
0
10
2.5
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Typical ADC Reference Levels. (The VINSIG Min and Max values
listed account for both the input common mode limits and the output clipping)
+V
–V
(V)
GAIN
(V/V)
V
(V)
V
V
V
V
V
OUTDIFF(MAX)
S
S
OCM
INREF
(V)
INSIG(MAX)
(V)
INSIG(MIN)
(V)
INSIGP-P(MAX)
(V)
2.7
2.7
2.7
2.7
5
(V AROUND V
P-P
)
(V
P-PDIFF
)
INREF
0
1
2
1
0
0
0
0
0
0
0
0
2.000
1.000
0.400
0.200
4.000
2.000
0.800
0.400
–2.000
–1.000
–0.400
–0.200
–4.000
–2.000
–0.800
–0.400
4.00
2.00
0.80
0.40
8.00
4.00
1.60
0.80
4.00
0
1
4.00
4.00
4.00
8.00
8.00
8.00
8.00
0
5
1
0
10
1
1
0
2
5
0
2
2
5
0
5
2
5
0
10
2
Fully Differential Amplifier Applications
Circuit Analysis
While mathematically correct, the basic signal equation
does not immediately yield any intuitive feel for fully
differential amplifier application operation. However, by
nulling out specific terms, some basic observations and
sensitivities come forth. Setting β1 equal to β2, VOSDIFF to
zero and VOUTCM to VOCM gives the old gain equation from
Figure 3. The ground referenced, single-ended input sig-
nal equation yields the interesting result that the driven
side feedback factor (β1) has a very different sensitivity
than the grounded side (β2). The CMRR is twice the
feedback factor difference divided by the feedback factor
sum. The differential output offset voltage has two terms.
The first term is determined by the input offset term,
All of the previous applications circuit discussions have
assumed perfectly matched symmetrical feedback net-
works. To consider the effects of mismatched or asym-
metricalfeedbacknetworks,theequationsgetabitmessier.
Figure 6 lists the basic gain equation for the differential
outputvoltageintermsof+VIN, –VIN, VOSDIFF, VOUTCM and
the feedback factors β1 and β2. The feedback factors are
simplytheportionoftheoutputthatisfedbacktotheinput
summingjunctionbytheRFB-RIN resistivevoltagedivider.
β1 and β2have the range of zero to one. The VOUTCM term
also includes its offset voltage, VOSCM, and its gain mis-
match term, KCM. The KCM term is determined by the
matching of the on-chip RCMP and RCMM resistors in the
common mode level servo (see Figure 2).
V
OSDIFF, and the application’s gain. Note that this term
equates to the formula in Figure 3 when β1 equals β2. The
amount of signal level shifting and the feedback factor
mismatch determines the second term. This term
1992f
35
LTC1992 Family
W U U
U
APPLICATIO S I FOR ATIO
R
FB2
R
IN2
IN1
+
–V
IN
+V
–V
–
OUT
V
V
INDIFF
OUTDIFF
+V – –V
LTC1992
V
OCM
V
OCM
+V – –V
IN
IN
OUT OUT
R
+V
IN
+
–
OUT
R
FB1
2[+V • (1 – β1) – (–V ) • (1 – β2)] + 2V
+ 2V
(β1 – β2)
IN
IN
OSDIFF
OUTCM
V
=
OUTDIFF
β1 + β2
WHERE:
R
R
IN2
IN1
β1 =
; β2 =
; V
V
= AMPLIFIER INPUT REFERRED OFFSET VOLTAGE
OSDIFF
R
+ R
R
+ R
IN1
FB1
IN2
FB2
= K • V
+ V
OSCM
OUTCM
CM OCM
0.999 < K < 1.001
CM
• FOR GROUND REFERENCED, SINGLE-ENDED INPUT SIGNAL, LET +V = V
IN INSIG
AND –V = 0V
IN
2 • V
INSIG
• (1 – β1) + 2V
OSDIFF
+ 2V (β1 – β2)
OUTCM
V
=
OUTDIFF
β1 + β2
• COMMON MODE REJECTION: SET +V = –V = V
, V
= 0V, V = 0V
OUTCM
IN
IN
INCM OSDIFF
∆V
β1 + β2
β2 – β1
INCM
CMRR =
= 2
; OUTPUT REFERRED
∆V
OUTDIFF
• OUTPUT DC OFFSET VOLTAGE: SET +V = –V = V
IN
IN
INCM
β2 – β1
β1 + β2
2
V
= V
OSDIFF
+ (V
– V ) 2
INCM
OSDIFFOUT
OUTCM
β1 + β2
Figure 6. Basic Equations for Mismatched or Asymmetrical Feedback Applications Circuits
quantifies the undesired effect of signal level shifting dual, split supply voltage applications with a ground
discussed earlier in the Signal Level Shifting section.
referenced input signal and a grounded VOCM pin.
The top application circuit in Figure 7 yields a high input
impedance, precision gain of 2 block without any external
resistors. The on-chip common mode feedback servo
resistors determine the gain precision (better than 0.1
percent). By using the –VOUT output alone, this circuit is
also useful to get a precision, single-ended output, high
input impedance inverter. To intuitively understand this
circuit, consider it as a standard op amp voltage follower
(delivered through the signal gain servo) with a comple-
mentary output (delivered through the common mode
level servo). As usual, the amplifier’s input common
mode range must not be exceeded. As with a standard op
amp voltage follower, the common mode signal seen at
the amplifier’s input is the input signal itself. This condi-
tion limits the input signal swing, as well as the output
signal swing, to be the input signal common mode range
specification.
Asymmetrical Feedback Application Circuits
The basic signal equation in Figure 6 also gives insight to
another piece of intuition. The feedback factors may be
deliberatelysettodifferentvalues. Oneinterestingclassof
these application circuits sets one or both of the feedback
factorstotheextremevaluesofeitherzeroorone.Figure 7
shows three such circuits.
At first these application circuits may look to be unstable
or open loop. It is the common mode feedback loop that
enables these circuits to function. While they are useful
circuits, they have some shortcomings that must be
considered. First, do to the severe feedback factor asym-
metry, the VOCM level influences the differential output
voltage with about the same strength as the input signal.
With this much gain in the VOCM path, differential output
offset and noise increase. The large VOCM to VOUTDIFF gain
also necessitates that these circuits are largely limited to
The middle circuit is largely the same as the first except
that the noninverting amplifier path has gain. Note that
1992f
36
LTC1992 Family
W U U
APPLICATIO S I FOR ATIO
U
+V
OUT
V
= 2(+V – V
)
OCM
+
–
–
OUTDIFF
IN
V
OCM
V
OCM
LTC1992
V
IN
–V
OUT
+
SETTING V
= 0V
OCM
V
V
= 2V
OUTDIFF
IN
R
R
IN
FB
R
1
IN
+V
= 2 +V
– V
OCM
; β =
+
–
–
OUT
OUTDIFF
IN
(
)
β
R
+ R
IN
FB
V
V
OCM
LTC1992
OCM
SETTING V
= 0V
1
OCM
V
IN
–V
OUT
+
R
FB
= 2V 1 +
V
= 2V
IN
OUTDIFF
IN
(
)
(
)
R
IN
β
1 – β
β
R
IN
+ R
+V
OUT
V
= 2 +V
+ V
OCM
; β =
+
–
OUTDIFF
IN
(
)
R
IN
FB
V
OCM
V
LTC1992
OCM
R
IN
SETTING V
= 0V
OCM
V
IN
–V
OUT
+
–
R
R
1 – β
FB
= 2V
IN
V
= 2V
IN
(
)
(
)
OUTDIFF
β
IN
R
FB
1992 F07
Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual,
Split Supplies (e.g., ±5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)
once the VOCM voltage is set to zero, the gain formula is Thebottomcircuitisanothercircuitthatutilizesastandard
the same as a standard noninverting op amp circuit op amp configuration with a complementary output. In
multiplied by two to account for the complementary this case, the standard op amp circuit has an inverting
output. Taking RFB to zero (i.e., taking β to one) gives the configuration. With VOCM at zero volts, the gain formula is
same formula as the top circuit. As in the top circuit, this the same as a standard inverting op amp circuit multiplied
circuit is also useful as a single-ended output, high input by two to account for the complementary output. This
impedance inverting gain block (this time with gain). The circuit does not have any common mode level constraints
input common mode considerations are similar to the top astheinvertinginputvoltagesetstheinputcommonmode
circuit’s, but are not nearly as constrained since there is level. This circuit also delivers rail-to-rail output voltage
now gain in the noninverting amplifier path. This circuit, swing without any concerns.
with VOCM at ground, also permits a rail-to-rail output
swing in most applications.
1992f
37
LTC1992 Family
U
TYPICAL APPLICATIO S
Interfacing a Bipolar, Ground Referenced, Single-Ended Signal to a Unipolar Single Supply,
Differential Input ADC (VIN = 0V Gives a Digital Mid-Scale Code)
5V
1µF
0.1µF
40k
10k
13.3k
1
8
3
100Ω
100Ω
10k
4
2
3
V
V
1
7
REF
CC
7
6
5
+IN
–IN
+
MID
–
SCK
SERIAL
DATA
V
V
100pF
LTC1864 SDO
LTC1992
2
8
OCM
LINK
2.5V
10k
CONV
GND
+
V
IN
0V
–
6
5
–2.5V
5V
4
1992 TA02a
13.3k
10k
0.1µF
40k
Compact, Unipolar Serial Data Conversion
5V
1µF
1
8
3
0.1µF
100Ω
100Ω
4
2
3
V
V
1
7
REF
CC
7
6
5
+IN
–IN
+
–
SCK
SERIAL
DATA
LINK
V
MID
100pF
LTC1864 SDO
LTC1992-2
2
8
V
OCM
2.5V
CONV
GND
+
V
IN
–
6
5
0V
4
1992 TA03a
0.1µF
Zero Components, Single-Ended Adder/Subtracter
+V
S
0.1µF
3
1
2
8
4
V
V
V1 = V + V – V
B C
+
–
A
B
A
C
V
LTC1992-2
OCM
V
+
V2 = V + V – V
–
C
B
A
5
6
0.1µF
–V
S
1992 TA04
1992f
38
LTC1992 Family
U
TYPICAL APPLICATIO S
Single-Ended to Differential Conversion Driving an ADC
2.2µF
10µF
5V 10µF
5V 10µF
10Ω
FFT of the Output Data
+
+
+
3
36
10
35
9
0
–10
–20
–30
–40
–50
–60
–70
–80
V
AV
AV
f
f
= 10.0099kHz
= 333kHz
DV
DD
DGND
SNR =85.3dB
THD = –72.1dB
SINAD = –72dB
REF
DD
DD
IN
SAMPLE
SHDN 33
CS 32
LTC1603
CONTROL
LOGIC
AND
TIMING
µP
CONTROL
LINES
CONVST 31
RD 30
REFCOMP
4.375V
7.5k
4
1
2.5V
REF
1.75X
5V
+
BUSY 27
47µF
0.1µF
100Ω
OV
DD
29
28
5V OR
–90
+
3
3V
–100
–110
–120
–130
–140
+
A
4
IN
10µF
1
7
OGND
+
MID
–
+
–
V
16-BIT
SAMPLING
ADC
OUTPUT
BUFFERS
100pF
B15 TO B0
16-BIT
LTC1992-1
2
8
V
PARALLEL
BUS
OCM
–
D15 TO D0
2
A
IN
0
10 20 30 40 50 60 70 80 90 100
+
V
IN
–
6
5
100Ω
0.1µF
11 TO 26
1992 TA06a
FREQUENCY (kHz)
AGND AGND AGND AGND
V
SS
34
1992 TA06b
5
6
7
8
10µF
–5V
+
–5V
U
PACKAGE DESCRIPTIO
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
0.889 ± 0.127
(.035 ± .005)
DETAIL “A”
0° – 6° TYP
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
GAUGE PLANE
0.52
(.0205)
REF
1.10
(.043)
MAX
0.86
(.034)
REF
8
7 6
5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.65
(.0256)
BSC
0.42 ± 0.038
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
SEATING
PLANE
(.0165 ± .0015)
0.18
(.007)
TYP
0.22 – 0.38
(.009 – .015)
TYP
0.127 ± 0.076
(.005 ± .003)
RECOMMENDED SOLDER PAD LAYOUT
0.65
(.0256)
BSC
MSOP (MS8) 0603
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
1
2
3
4
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
1992f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
39
LTC1992 Family
U
TYPICAL APPLICATIO
Balanced Frequency Converter (Suitable for Frequencies up to 50kHz)
60kHz LOW PASS FILTER
5V
SAMPLER
2kHz LOWPASS FILTER
0.1µF
9.53k
0.1µF
0.1µF
75k
120pF
4
+
390pF
V
3
9.53k
9.53k
8.87k
1
7
2
8
4
7
8
BNC
BNC
3
+
–
–
MID
37.4k
60.4k
1
7
2
8
4
11
V
+
–
OUTP
V
330pF
8.87k
LTC1992
V
MID
BNC
V
OCM
180pF
60.4k
LTC1992
1/2 LTC1043
13
V
OCM
V
INP
+
37.4k
12
5
6
V
+
–
OUTM
14
16
5
6
CLK
–
120pF
9.53k
V
390pF
75k
17
0.1µF
0.1µF
0.1µF
10k
0.1µF
V
OCM
1992 TA05a
CLK
–5V
V
= 24kHz
INP
0V
(1V/DIV)
CLK = 25kHz
(LOGIC SQUARE WAVE)
(5V/DIV)
0V
0V
0V
V
= 1kHz
OUTP
(0.5V/DIV)
= 1kHz
V
OUTM
(0.5V/DIV)
1992 TA05b
200µs/DIV
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
Single Resistor Sets the Gain
LT1167
Precision Instrumentation Amplifier
LT1990
High Voltage, Gain Selectable Difference Amplifier
Precision Gain Selectable Difference Amplifier
High Speed Gain Selectable Difference Amplifier
Differential In/Out Amplifier Lowpass Filter
±250V Common Mode, Micropower, Selectable Gain = 1, 10
Micropower, Pin Selectable Gain = –13 to 14
LT1991
LT1995
30MHz, 1000V/µs, Pin Selectable Gain = –7 to 8
Very Low Noise, Standard Differential Amplifier Pinout
LT6600-X
1992f
LT/TP 0105 1K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
40
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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