LT1793IN8 [Linear]
Low Noise, Picoampere Bias Current, JFET Input Op Amp; 低噪声， Picoampere偏置电流， JFET输入运算放大器
| 型号： | LT1793IN8 |
| 厂家： | 
Linear |
| 描述： | Low Noise, Picoampere Bias Current, JFET Input Op Amp |
| 文件： | 总12页 (文件大小：165K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1793
Low Noise,
Picoampere Bias Current,
JFET Input Op Amp
U
FEATURES
DESCRIPTIO
The LT®1793 achieves a new standard of excellence in
noiseperformanceforaJFETopamp.Forthefirsttimelow
voltage noise (6nV/√Hz) is simultaneously offered with
extremely low current noise (0.8fA/√Hz), providing the
lowest total noise for high impedance transducer applica-
tions. Unlike most JFET op amps, the very low input bias
current (3pA typ) is maintained over the entire common
moderangewhichresultsinanextremelyhighinputresis-
tance (1013Ω). When combined with a very low input ca-
pacitance (1.5pF) an extremely high input impedance
results, making the LT1793 the first choice for amplifying
low level signals from high impedance transducers. The
lowinputcapacitancealsoassureshighgainlinearitywhen
buffering AC signals from high impedance transducers.
■
Input Bias Current, Warmed Up: 10pA Max
■
100% Tested Low Voltage Noise: 8nV/√Hz Max
■
A Grade 100% Temperature Tested
■
Offset Voltage Over Temp: 1mV Max
Input Resistance: 1013Ω
■
■
Very Low Input Capacitance: 1.5pF
■
Voltage Gain: 1 Million Min
■
Gain-Bandwidth Product: 4.2MHz Typ
■
Guaranteed Specifications with ±5V Supplies
U
APPLICATIO S
■
Photocurrent Amplifiers
■
Hydrophone Amplifiers
■
High Sensitivity Piezoelectric Accelerometers
TheLT1793isunconditionallystableforgainsof1ormore,
even with 1000pF capacitive loads. Other key features are
250µV VOS and a voltage gain over 4 million. Each indi-
vidual amplifier is 100% tested for voltage noise, slew rate
(3.4V/µs) and gain-bandwidth product (4.2MHz).
■
Low Voltage and Current Noise Instrumentation
Amplifier Front Ends
■
Two and Three Op Amp Instrumentation Amplifiers
■
Active Filters
, LTC and LT are registered trademarks of Linear Technology Corporation.
Specifications at ±5V supply operation are also provided.
ForanevenlowervoltagenoisepleaseseetheLT1792data
sheet.
U
TYPICAL APPLICATIO
Low Noise Light Sensor with DC Servo
C1
2pF
1kHz Output Voltage Noise
Density vs Source Resistance
10k
+
V
R1
1M
–
–
+
2
3
7
V
N
1k
100
10
+
6
V
LT1793
OUT
R
SOURCE
C2 0.022µF
D2
1N914
4
–
+
V
V
R2
100k
C
D
–
D1
1N914
R3
1k
V
N
2N3904
LT1097
SOURCE
T
= 25°C
= ±15V
A
S
+
RESISTANCE
ONLY
V
HAMAMATSU
S1336-5BK
(908) 231-0960
R5
R4
10k 1k
1
100
1k 10k 100k 1M 10M
1G
100M
–
1793 TA01
V
R2C2 > C1R1
SOURCE RESISTANCE (Ω)
C
V
= PARASITIC PHOTODIODE CAPACITANCE
= 100mV/µWATT FOR 200nm WAVE LENGTH
D
OUT
2
2
–
V
N
=
√
(V
OP AMP
)
+ 4kTR + 2qI R
V
S
B
S
330mV/µWATT FOR 633nm WAVE LENGTH
1793 TA02
1
LT1793
ABSOLUTE AXI U RATI GS
W W W
U
(Note 1)
Specified Temperature Range
Supply Voltage ..................................................... ±20V
Differential Input Voltage ...................................... ±40V
Input Voltage (Equal to Supply Voltage)............... ±20V
Output Short-Circuit Duration ........................ Indefinite
Operating Temperature Range............... –40°C to 85°C
Commercial (Note 8) ......................... – 40°C to 85°C
Industrial ........................................... – 40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................ 300°C
W
U
/O
PACKAGE RDER I FOR ATIO
ORDER PART
NUMBER
ORDER PART
NUMBER
TOP VIEW
TOP VIEW
V
OS
ADJ
V
OS
ADJ
NC
1
2
3
4
8
7
6
5
1
2
3
4
NC
8
7
6
5
LT1793ACS8
LT1793CS8
LT1793AIS8
LT1793IS8
LT1793ACN8
LT1793CN8
LT1793AIN8
LT1793IN8
+
–IN A
+IN A
–IN A
+IN A
V+
V
A
A
OUT
OUT
–
–
V
V
V
OS
ADJ
V
OS
ADJ
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
S8 PART MARKING
1793A 1793AI
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 80°C/W
TJMAX = 160°C, θJA = 190°C/W
1793
1793I
Consult factory for Military grade parts.
TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
LT1793AC/LT1793AI
LT1793C/LT1793I
SYMBOL PARAMETER
CONDITIONS (Note 2)
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
V
Input Offset Voltage
Input Offset Current
Input Bias Current
0.25
0.45
0.8
1.4
0.25
0.45
0.9
1.6
mV
mV
OS
V = ±5V
S
I
I
Warmed Up (Note 3)
T = 25°C (Note 6)
J
1.5
0.5
7
2
2.5
0.7
15
4
pA
pA
OS
Warmed Up (Note 3)
T = 25°C (Note 6)
J
3
1
10
3
4.0
1.5
20
5
pA
pA
B
e
Input Noise Voltage
0.1Hz to 10Hz
2.4
2.4
µV
P-P
n
Input Noise Voltage Density
f = 10Hz
f = 1000Hz
O
11.5
6
11.5
6
nV/√Hz
nV/√Hz
O
8
8
i
Input Noise Current Density
f = 10Hz, f = 1kHz (Note 4)
0.8
1
fA/√Hz
n
O
O
R
Input Resistance
Differential Mode
Common Mode
IN
14
14
10
10
Ω
Ω
13
13
V
CM
= –10V to 13V
10
10
C
V
Input Capacitance
1.5
2.0
1.5
2.0
pF
pF
IN
V = ±5V
S
Input Voltage Range (Note 5)
13.0
13.5
–10.5 –11.0
13.0
13.5
– 10.5 – 11.0
V
V
CM
CMRR
PSRR
Common Mode Rejection Ratio
Power Supply Rejection Ratio
V
= –10V to 13V
83
85
102
98
81
83
96
95
dB
dB
CM
V = ±4.5V to ± 20V
S
2
LT1793
TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
LT1793AC/LT1793AI
LT1793C/LT1793I
SYMBOL PARAMETER
CONDITIONS (Note 2)
V = ±12V, R = 10k
MIN
1000 4500
500 3500
TYP
MAX
MIN
TYP
MAX
UNITS
A
V
Large-Signal Voltage Gain
Output Voltage Swing
900
400
4400
3000
V/mV
V/mV
VOL
OUT
O
L
V = ±10V, R = 1k
O
L
R = 10k
±13.0 ±13.2
±12.0 ±12.3
±13.0 ±13.2
±12.0 ±12.3
V
V
L
R = 1k
L
SR
Slew Rate
R ≥ 2k (Note 7)
2.3
2.5
3.4
4.2
2.3
2.5
3.4
4.2
V/µs
L
GBW
Gain-Bandwidth Product
Supply Current
f = 100kHz
O
MHz
I
4.2
4.2
5.20
5.15
4.2
4.2
5.20
5.15
mA
mA
S
V = ±5V
S
Offset Voltage
R
(to V ) = 10k
13
13
mV
POT
EE
Adjustment Range
The ● denotes specifications which apply over the temperature range 0°C ≤ TA ≤ 70°C, otherwise specifications are at TA = 25°C.
VS = ±15V, VCM = 0V, unless otherwise noted. (Note 9)
LT1793AC
TYP
LT1793C
TYP
SYMBOL PARAMETER
CONDITIONS (Note 2)
MIN
MAX
MIN
MAX
UNITS
V
Input Offset Voltage
●
●
0.50
0.75
1.0
1.6
1.0
1.6
3.5
4.2
mV
mV
OS
V = ±5V
S
∆V
∆Temp
Average Input Offset
Voltage Drift
(Note 6)
●
5
13
8
50
µV/°C
OS
I
I
Input Offset Current
●
●
15
100
400
20
130
500
pA
pA
OS
B
Input Bias Current
130
13.4
–10.0 –10.8
150
13.4
– 10.0 – 10.8
V
Input Voltage Range (Note 5)
●
●
12.9
12.9
V
V
CM
CMRR
PSRR
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Large-Signal Voltage Gain
V
= –10V to 12.9V
●
●
79
83
100
97
77
81
95
94
dB
dB
CM
V = ±4.5V to ± 20V
S
A
V = ±12V, R = 10k
V = ±10V, R = 1k
●
●
900
500
3600
2600
800
400
3400
2400
V/mV
V/mV
VOL
O
L
O
L
V
Output Voltage Swing
R = 10k
R = 1k
L
●
●
±12.9 ±13.2
±11.9 ±12.15
±12.9 ±13.2
±11.9 ±12.15
V
V
OUT
L
SR
Slew Rate
R ≥ 2k (Note 7)
●
●
2.2
2.2
3.3
3.3
2.2
2.2
3.3
3.3
V/µs
L
GBW
Gain-Bandwidth Product
Supply Current
f = 100kHz
O
MHz
I
●
●
4.2
4.2
5.30
5.25
4.2
4.2
5.30
5.25
mA
mA
S
V = ±5V
S
3
LT1793
The ● denotes specifications which apply over the temperature range
ELECTRICAL CHARACTERISTICS
–40°C ≤ TA ≤ 85°C. VS = ±15V, VCM = 0V, unless otherwise noted. (Notes 8, 9)
LT1793AC/LT1793AI
LT1793C/LT1793I
SYMBOL PARAMETER
CONDITIONS (Note 2)
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
V
Input Offset Voltage
●
●
0.65
1.00
1.3
1.9
1.6
2.0
4.8
5.5
mV
mV
OS
V = ±5V
S
∆V
∆Temp
Average Input Offset
Voltage Drift
(Note 6)
●
5
13
9
50
µV/°C
OS
I
I
Input Offset Current
●
●
80
300
100
800
13.0
400
pA
pA
OS
B
Input Bias Current
700
13.0
–10.0 –10.5
2400
3000
V
Input Voltage Range (Note 5)
●
●
12.6
12.6
V
V
CM
– 10.0 – 10.5
CMRR
PSRR
Common Mode Rejection Ratio
Power Supply Rejection Ratio
Large-Signal Voltage Gain
V
= –10V to 12.6V
●
●
78
81
99
96
76
79
94
93
dB
dB
CM
V = ±4.5V to ± 20V
S
A
V = ±12V, R = 10k
V = ±10V, R = 1k
●
●
850
400
3300
2200
750
300
3000
2000
V/mV
V/mV
VOL
O
L
O
L
V
Output Voltage Swing
R = 10k
R = 1k
L
●
●
±12.8 ±13.1
±11.8 ±12.1
±12.8 ±13.1
±11.8 ±12.1
V
V
OUT
L
SR
Slew Rate
R ≥ 2k
●
●
2.1
2
3.2
3.1
2.1
2
3.2
3.1
V/µs
L
GBW
Gain-Bandwidth Product
Supply Current
f = 100kHz
O
MHz
I
●
●
4.2
4.2
5.40
5.35
4.2
4.2
5.40
5.35
mA
mA
S
V = ±5V
S
Note 6: This parameter is not 100% tested.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 7: Slew rate is measured in A = –1; input signal is ±7.5V, output
V
measured at ±2.5V.
Note 2: Typical parameters are defined as the 60% yield of parameter
distributions of individual amplifiers.
Note 8: The LT1793AC and LT1793C are guaranteed to meet specified
performance from 0°C to 70°C and are designed, characterized and
expected to meet these extended temperature limits, but are not tested at
–40°C and 85°C. The LT1793I is guaranteed to meet the extended
temperature limits. The LT1793AC and LT1793AI grade are 100%
temperature tested for the specified temperature range.
Note 9: The LT1793 is measured in an automated tester in less than one
second after application of power. Depending on the package used, power
dissipation, heat sinking, and air flow conditions, the fully warmed-up chip
temperature can be 10°C to 50°C higher than the ambient temperature.
Note 3: I and I readings are extrapolated to a warmed-up temperature
B
OS
from 25°C measurements and 32°C characterization data.
Note 4: Current noise is calculated from the formula:
1/2
i = (2qI )
n
B
–19
where q = 1.6 • 10
coulomb. The noise of source resistors up to 200M
swamps the contribution of current noise.
Note 5: Input voltage range functionality is assured by testing offset
voltage at the input voltage range limits to a maximum of 2.3mV
(A grade) to 2.8mV (C grade).
4
LT1793
U W
TYPICAL PERFOR A CE CHARACTERISTICS
1kHz Input Noise Voltage
Distribution
0.1Hz to 10Hz Voltage Noise
Voltage Noise vs Frequency
100
10
1
50
40
30
20
10
0
T
= 25°C
= ±15V
A
S
T
= 25°C
= ±15V
A
S
V
V
510 OP AMPS TESTED
1/f CORNER
30Hz
0
2
4
6
8
10
1
10
100
FREQUENCY (Hz)
1k
10k
4.2 4.6 5.0 5.4 5.8 6.2 6.6 7.0 7.4 7.8 8.2
INPUT VOLTAGE NOISE (nV/√Hz)
1793 G02
TIME (SEC)
1793 G03
1793 G01
Voltage Noise
Common Mode Limit
vs Temperature
Common Mode Rejection Ratio
vs Frequency
vs Chip Temperature
+
120
100
V
0
–0.5
–1.0
–1.5
10
9
T
= 25°C
= ±15V
A
V
= ±15V
S
V
S
+
V
= 5V TO 20V
8
80
60
40
20
0
7
–2.0
6
4.0
3.5
5
–
4
V
= –5V TO –20V
3.0
3
2.5
–
V
+2.0
2
1k
10k
100k
FREQUENCY (Hz)
1M
10M
–60
–20
20
60
100
140
50 75
TEMPERATURE (°C)
–75 –50 –25
0
25
100 125
TEMPERATURE (°C)
1793 G06
1793 G05
1793 G04
Power Supply Rejection Ratio
vs Frequency
Gain and Phase Shift
vs Frequency
Voltage Gain vs Frequency
120
100
80
60
40
20
0
180
160
140
120
100
80
50
40
30
20
10
0
80
T
V
C
= 25°C
= ±15V
= 10pF
T
V
C
= 25°C
= ±15V
= 10pF
A
S
L
A
S
L
T
= 25°C
A
100
120
140
160
180
200
+PSRR
PHASE
–PSRR
60
40
GAIN
20
0
–10
–20
10
1k
10k 100k
1M
10M
100
0.01
1
100
10k
1M
100M
0.1
1
10
100
FREQUENCY (Hz)
FREQUENCY (MHz)
FREQUENCY (Hz)
1793 G07
1793 G08
1793 G09
5
LT1793
TYPICAL PERFOR A CE CHARACTERISTICS
U W
Output Voltage Swing
vs Load Current
Large-Signal Transient Response
Small-Signal Transient Response
+
V
–0.8
–1.0
–1.2
–1.4
–1.6
2.0
125°C
25°C
–55°C
V
= ±5V TO ±20V
S
1.8
1.6
125°C
25°C
1.4
1793 G11
1793 G10
AV = 1
5µs/DIV
AV = 1
CL = 10pF
VS = ±15V, ±5V
1µs/DIV
1.2
–55°C
–6 –4
CL = 10pF
RL = 2k
–
V
+1.0
V
S = ±15V
0
2
4
8
–10 –8
–2
6
I
10
I
SINK
SOURCE
OUTPUT CURRENT (mA)
1793 G12
THD and Noise Frequency for
Noninverting Gain
Warm-Up Drift
Capacitive Load Handling
1
0.1
90
75
60
45
30
15
0
50
40
30
20
10
0
V
= ±15V
= 25°C
≥ 10k
= 100mV
= 10
V
= ±15V
= 25°C
Z
V
A
= 2k 15pF
S
A
L
O
V
F
S
A
L
O
V
T
T
= 20V
P-P
R
V
A
= 1, 10, 100
MEASUREMENT BANDWIDTH
= 10Hz TO 80kHz
SO-8 PACKAGE
N8 PACKAGE
P-P
R = 10k
C = 20pF
F
A
= 100
V
0.01
0.001
A
= 10
A
= 1
V
V
A
= 1
V
NOISE FLOOR
1k
A
= 10
V
0.0001
0
2
3
4
5
6
0.1
1
10
100
1000 10000
1
20
100
10k 20k
TIME AFTER POWER ON (MINUTES)
FREQUENCY (Hz)
CAPACITIVE LOAD (pF)
1793 G15
1793 G14
1793 G13
THD and Noise vs Frequency for
Inverting Gain
THD and Noise vs Output
THD and Noise vs Output
Amplitude for Noninverting Gain
Amplitude for Inverting Gain
1
1
1
0.1
Z
V
A
= 2k 15pF
Z
= 2k 15pF, f = 1kHz
O
= –1, –10, –100
Z
= 2k 15pF, f = 1kHz
L
O
V
L
V
L O
= 20V
A
A
= 1, 10, 100
V
P-P
= –1, –10, –100
MEASUREMENT BANDWIDTH
= 10Hz TO 22kHz
MEASUREMENT BANDWIDTH
= 10Hz TO 22kHz
MEASUREMENT BANDWIDTH
= 10Hz TO 80kHz
0.1
0.01
0.1
0.01
A
= –100
A
= –100
A
V
= 100
V
V
0.01
A
= 10
= 1
V
A
= –10
V
A
= –10
V
A
= –1
0.001
0.0001
V
0.001
0.0001
0.001
0.0001
A
V
A
= –1
V
NOISE FLOOR
20
100
1k
10k 20k
0.3
1
10
)
30
0.3
1
10
30
FREQUENCY (Hz)
OUTPUT SWING (V
OUTPUT SWING (V
)
P-P
P-P
1793 G16
1793 G17
1793 G18
6
LT1793
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Short-Circuit Output Current
vs Temperature
Input Bias and Offset Currents
vs Chip Temperature
Supply Current vs Temperature
30n
10n
40
35
30
25
20
15
10
5
V
= ±15V
S
V
V
= ±15V
CM
S
= –10 TO 13V
3n
1n
BIAS
CURRENT
V
= ±15V
= ±5V
300p
100p
S
SINK
SOURCE
4
V
S
30p
10p
3p
OFFSET
CURRENT
1p
3
0.3p
75 100
75 100
0
25
75
TEMPERATURE (°C)
100
125
–75 –50 –25
0
25 50
125
–75 –50 –25
0
25 50
125
50
TEMPERATURE (°C)
TEMPERATURE (°C)
1793 G21
1793 G19
1793 G20
W
U
O U
I FOR ATIO
S
PPLICATI
A
The extremely high input impedance (1013Ω) assures that
the input bias current is almost constant over the entire
common mode range. Figure 1 shows how the LT1793
standsuptothecompetition.Unlikethecompetition,asthe
input voltage is swept across the entire common mode
range the input bias current of the LT1793 hardly changes.
As a result the current noise does not degrade. This makes
the LT1793 the best choice in applications where an
amplifier has to buffer signals from a high impedance
transducer.
LT1793 vs the Competition
With improved noise performance, the LT1793 in the
PDIP directly replaces such JFET op amps as the OPA111
and the AD645. The combination of low current and
voltagenoiseoftheLT1793allowsittosurpassmostdual
and single JFET op amps. The LT1793 can replace many
of the lowest noise bipolar amps that are used in amplify-
ing low level signals from high impedance transducers.
The best bipolar op amps (with higher current noise) will
eventually lose out to the LT1793 when transducer im-
pedance increases.
Offsetnullingwillbecompatiblewiththesedeviceswiththe
wiper of the potentiometer tied to the negative supply
(Figure 2a). No appreciable change in offset voltage drift
100
CURRENT NOISE = √2qI
B
80
60
40
20
15V
15V
OP215
LT1793
–
+
–
+
2
3
2
3
7
7
6
6
0
–20
4
4
AD822
5
5
–40
–60
∆V = ±13mV
∆V = ±1.3mV
OS
OS
1
1
50k
–15V
10k 10k
50k
–80
–100
–15
–10
0
5
10
15
–5
COMMON MODE RANGE (V)
–15V
1793 F02
1793 F01
(a)
(b)
Figure 1. Comparison of LT1793, OP215, and AD822
Input Bias Current vs Common Mode Range
Figure 2
7
LT1793
PPLICATI
with temperature will occur when the device is nulled with
a potentiometer ranging from 10k to 200k. Finer adjust-
ments can be made with resistors in series with the
potentiometer (Figure 2b).
W
U
O U
I FOR ATIO
S
A
voltagenoise, thethermalnoiseofthetransducer, andthe
op amp’s input bias current noise times the transducer
impedance. Figure 3 shows total input voltage noise
versus source resistance. In a low source resistance
(<5k) application the op amp voltage noise will dominate
the total noise. This means the LT1793 is superior to
most JFET op amps. Only the lowest noise bipolar op
amps have the advantage at low source resistances. As
the source resistance increases from 5k to 50k, the
LT1793 will match the best bipolar op amps for noise
performance, since the thermal noise of the transducer
(4kTR) begins to dominate the total noise. A further
increase in source resistance, above 50k, is where the op
amp’s current noise component (2qIBR2) will eventually
dominate the total noise. At these high source resis-
tances, the LT1793 will out perform the lowest noise
bipolar op amps due to the inherently low current noise of
FET input op amps. Clearly, the LT1793 will extend the
range of high impedance transducers that can be used for
high signal-to-noise ratios. This makes the LT1793 the
best choice for high impedance, capacitive transducers.
Amplifying Signals from High Impedance Transducers
The low voltage and current noise offered by the LT1793
makes it useful in a wide range of applications, especially
where high impedance, capacitive transducers are used
such as hydrophones, precision accelerometers and
photodiodes. The total output noise in such a system is
thegaintimestheRMSsumoftheopamp’sinputreferred
10k
C
LT1007*
S
–
+
R
LT1793*
S
1k
100
10
V
O
R
C
S
S
LT1007†
LT1793
LT1793†
LT1007
RESISTOR NOISE ONLY
Optimization Techniques for Charge Amplifiers
1
The high input impedance JFET front end makes the
LT1793 suitable in applications where very high charge
sensitivity is required. Figure 4 illustrates the LT1793 in its
inverting and noninverting modes of operation. A charge
amplifier is shown in the inverting mode example; the gain
depends on the principal of charge conservation at the
input of the LT1793. The charge across the transducer
capacitance CS is transferred to the feedback capacitor CF
100
1k 10k 100k 1M 10M 100M 1G
SOURCE RESISTANCE (Ω)
1793 F03
SOURCE RESISTANCE = 2R = R
S
* PLUS RESISTOR
†
PLUS RESISTOR
1000pF CAPACITOR
2
2
V = A √V
n
+ 4kTR + 2qI R
B
V
n (OP AMP)
Figure 3. Comparison of LT1793 and LT1007 Total Output
1kHz Voltage Noise vs Source Resistance
R
R2
F
C
B
C
F
R
B
–
+
–
+
R
C
OUTPUT
R1
OUTPUT
S
S
C
= C
C
S
S
B
B
F
F
TRANSDUCER
R
= R
R
R
C
S
C
R
R
C
S
S
dQ
Q = CV; = I = C
dt
dV
dt
B
B
S
= R
S
R
B
C
B
> R1 OR R2
TRANSDUCER
1793 F04
Figure 4. Inverting and Noninverting Gain Configurations
8
LT1793
W
U
O U
I FOR ATIO
S
PPLICATI
A
resultinginachangeinvoltagedV, whichisequaltodQ/CF.
The gain therefore is CF/CS. For unity-gain, the CF should
equal the transducer capacitance plus the input capaci-
tance of the LT1793 and RF should equal RS.
forRB isdeterminedbyequatingthethermalnoise(4kTRS)
2
to the current noise (2qIB) times RS . Solving for RS
results in RB = RS = 2VT/IB (VT = 26mV at 25°C). A parallel
capacitor CB, is used to cancel the phase shift caused by
the op amp input capacitance and RB.
In the noninverting mode example, the transducer current
is converted to a change in voltage by the transducer
capacitance, CS. This voltage is then buffered by the
LT1793 with a gain of 1 + R1/R2. A DC path is provided by
RS, which is either the transducer impedance or an exter-
nal resistor. Since RS is usually several orders of magni-
tudegreaterthantheparallelcombinationofR1andR2,RB
is added to balance the DC offset caused by the noninvert-
ing input bias current and RS. The input bias currents,
althoughsmallatroomtemperature,cancreatesignificant
errors at higher temperature, especially with transducer
resistances of up to 1000M or more. The optimum value
Reduced Power Supply Operation
Totakefulladvantageofawideinputcommonmoderange,
the LT1793 was designed to eliminate phase reversal.
Referring to the photographs in Figure 5, the LT1793 is
shown operating in the follower mode (AV = 1) at ±5V
supplies with the input swinging ±5.2V. The output of the
LT1793 clips cleanly and recovers with no phase reversal.
This has the benefit of preventing lockup in servo systems
and minimizing distortion components.
Input: ±5.2V Sine Wave
LT1793 Output
LT1793 F05a
LT1793 F05b
Figure 5. Voltage Follower with Input Exceeding the Common Mode Range (VS = ±5V)
9
LT1793
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
8
7
6
5
4
0.255 ± 0.015*
(6.477 ± 0.381)
1
2
3
0.130 ± 0.005
0.300 – 0.325
0.045 – 0.065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.255)
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
0.125
0.020
(0.508)
MIN
(3.175)
MIN
+0.035
0.325
–0.015
0.100 ± 0.010
(2.540 ± 0.254)
0.018 ± 0.003
(0.457 ± 0.076)
+0.889
8.255
(
)
N8 1197
–0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
10
LT1793
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.053 – 0.069
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
SO8 0996
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresenta-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT1793
TYPICAL APPLICATIONS N
U
10Hz Fourth Order Chebyshev Lowpass Filter (0.01dB Ripple)
R2
237k
R5
154k
15V
7
R1
R3
249k
C1
237k
33nF
–
+
2
3
R4
154k
R6
C3
V
IN
249k
10nF
–
+
6
2
3
LT1793
C2
100nF
6
C4
330nF
V
OUT
LT1793
4
1793 TA04
–15V
TYPICAL OFFSET ≈ 0.8mV
1% TOLERANCES
FOR V = 10V , V
= –121dB AT f > 330Hz
= – 6dB AT f = 16.3Hz
IN
P-P OUT
LOWER RESISTOR VALUES WILL RESULT IN LOWER THERMAL NOISE AND LARGER CAPACITORS
Accelerometer Amplifier with DC Servo
C1
1250pF
R1
100M
R2
18k
C2
2µF
R3
2k
R4
20M
–
2
1
R5
1/2 LT1464+ 3
20M
5V TO 15V
7
ACCELEROMETER
B & K MODEL 4381
OR EQUIVALENT
(800) 442-1030
C3
2µF
–
2
3
6
LT1793
+
OUTPUT
1793 TA03
4
R4C2 = R5C3 > R1 (1 + R2/R3) C1
OUTPUT = 0.8mV/pC* = 8.0mV/g**
DC OUTPUT ≤ 1.9mV
–5V TO –15V
OUTPUT NOISE = 8nV/√Hz AT 1kHz
*PICOCOULOMBS
**g = EARTH’S GRAVITATIONAL CONSTANT
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1113
Low Noise, Dual JFET Op Amp
Low Noise, Dual JFET Op Amp
Micropower Dual JFET Op Amp
Low Noise, Single JFET Op Amp
Dual Version of LT1792, V
Dual Version of LT1793, V
= 4.5nV/√Hz
NOISE
LT1169
= 6nV/√Hz, I = 10pA
NOISE
B
LT1467
1MHz, 2pA Max I , 200µA Max I
B
S
LT1792
Lower V
Version of LT1793, V
= 4.2nV/√Hz
NOISE
NOISE
1793f LT/TP 0599 4K • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
LINEAR TECHNOLOGY CORPORATION 1999
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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