LT6600CS8-5 [Linear]
Very Low Noise, Differential Amplifi er and 5MHz Lowpass Filter; 非常低噪声,差分功率放大器ER和5MHz的低通滤波器型号: | LT6600CS8-5 |
厂家: | Linear |
描述: | Very Low Noise, Differential Amplifi er and 5MHz Lowpass Filter |
文件: | 总12页 (文件大小:154K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LT6600-5
Very Low Noise, Differential
Amplifier and 5MHz Lowpass Filter
FEATURES
DESCRIPTION
TheLT®6600-5combinesafullydifferentialamplifierwitha
4thorder5MHzlowpassfilterapproximatinga Chebyshev
frequency response. Most differential amplifiers require
many precision external components to tailor gain and
bandwidth. In contrast, with the LT6600-5, two external
resistors program differential gain, and the filter’s 5MHz
cutoff frequency and passband ripple are internally set.
The LT6600-5 also provides the necessary level shifting
to set its output common mode voltage to accommodate
the reference voltage requirements of A/Ds.
n
Programmable Differential Gain via Two External
Resistors
n
Adjustable Output Common Mode Voltage
Operates and Specified with 3V, 5V, 5V Supplies
0.5dB Ripple 4th Order Lowpass Filter with 5MHz
n
n
Cutoff
n
82dB S/N with 3V Supply and 2V Output
Low Distortion, 2V , 800Ω Load
P-P
n
P-P
1MHz: 93dBc 2nd, 96dBc 3rd
Fully Differential Inputs and Outputs
Compatible with Popular Differential Amplifier
Pinouts
n
n
Using a proprietary internal architecture, the LT6600-5
integrates an antialiasing filter and a differential ampli-
fier/driver without compromising distortion or low noise
performance. At unity gain the measured in band sig-
nal-to-noise ratio is an impressive 82dB. At higher gains
the input referred noise decreases so the part can process
smaller input differential signals without significantly
degrading the output signal-to-noise ratio.
n
Available in an SO-8 Package
APPLICATIONS
n
High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Base Station Applications
n
High Speed Test and Measurement Equipment
Medical Imaging
Drop-in Replacement for Differential Amplifiers
The LT6600-5 also features low voltage operation. The
differential design provides outstanding performance for
n
n
a 2V signal level while the part operates with a single
P-P
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
3V supply.
For similar devices with other cutoff frequencies, refer to
the LT6600-20, LT6600-10 and LT6600-2.5.
TYPICAL APPLICATION
Dual, Matched, 5MHz Lowpass Filter
5MHz Phase Distribution
(50 Units)
3V
0.1μF
30
25
20
15
10
5
R
IN
3
1
4
–
+
0.01μF
7
2
8
I
IN
LT6600-5
Q
OUT
–
6
+
5
R
IN
806ꢀ
GAIN =
R
V
IN
OCM
(1V-1.5V)
3V 0.1μF
R
3
4
IN
1
–
+
LT6600-5
–
0.01μF
7
2
8
Q
I
IN
OUT
0
–135 –134.5–134–133.5–133–132.5–132–131.5
+
5
5MHz PHASE (DEG)
R
6
IN
66005 TA01
66005fa
1
LT6600-5
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
Total Supply Voltage .................................................11V
–
+
Input Voltage (Note 8)............................................... V
IN
1
2
3
4
8
7
6
5
IN
S
Input Current (Note 8).......................................... 10mA
Operating Temperature Range (Note 6)....–40°C to 85°C
Specified Temperature Range (Note 7) .... –40°C to 85°C
Junction Temperature ........................................... 150°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
V
V
V
OCM
MID
–
+
V
+
–
OUT
OUT
S8 PACKAGE
8-LEAD PLASTIC SO
T
= 150°C, θ = 100°C/W
JMAX
JA
ORDER INFORMATION
LEAD FREE FINISH
LT6600CS8-5#PBF
LT6600IS8-5#PBF
LEAD BASED FINISH
LT6600CS8-5
TAPE AND REEL
PART MARKING
66005
PACKAGE DESCRIPTION
8-Lead Plastic SO
SPECIFIED TEMPERATURE RANGE
–40°C to 85°C
LT6600CS8-5#TRPBF
LT6600IS8-5#TRPBF
TAPE AND REEL
6600I5
8-Lead Plastic SO
–40°C to 85°C
PART MARKING
66005
PACKAGE DESCRIPTION
8-Lead Plastic SO
SPECIFIED TEMPERATURE RANGE
–40°C to 85°C
LT6600CS8-5#TR
LT6600IS8-5#TR
LT6600IS8-5
6600I5
8-Lead Plastic SO
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k.
PARAMETER
Filter Gain, V = 3V
CONDITIONS
= 2V , f = DC to 260kHz
MIN
– 0.5
–0.15
–0.4
– 0.7
–1.1
TYP
0
MAX
0.5
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
V
IN
S
P-P IN
l
l
l
l
l
l
= 2V , f = 500k (Gain Relative to 260kHz)
0
0.1
P-P IN
= 2V , f = 2.5MHz (Gain Relative to 260kHz)
– 0.1
– 0.1
–0.2
– 28
–44
0
0.3
P-P IN
= 2V , f = 4MHz (Gain Relative to 260kHz)
0.6
P-P IN
= 2V , f = 5MHz (Gain Relative to 260kHz)
0.8
P-P IN
= 2V , f = 15MHz (Gain Relative to 260kHz)
–25
P-P IN
= 2V , f = 25MHz (Gain Relative to 260kHz)
P-P IN
Filter Gain, V = 5V
= 2V , f = DC to 260kHz
–0.5
– 0.15
–0.4
0.5
0.1
0.3
0.6
0.8
–25
S
P-P IN
l
l
l
l
l
l
= 2V , f = 500k (Gain Relative to 260kHz)
0
P-P IN
= 2V , f = 2.5MHz (Gain Relative to 260kHz)
–0.1
–0.1
–0.2
–28
–44
–0.1
P-P IN
= 2V , f = 4MHz (Gain Relative to 260kHz)
– 0.7
– 1.1
P-P IN
= 2V , f = 5MHz (Gain Relative to 260kHz)
P-P IN
= 2V , f = 15MHz (Gain Relative to 260kHz)
P-P IN
= 2V , f = 25MHz (Gain Relative to 260kHz)
P-P IN
Filter Gain, V = 5V
= 2V , f = DC to 260kHz
–0.6
0.4
S
P-P IN
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2
LT6600-5
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k.
PARAMETER
CONDITIONS
= 2V , f = DC to 260kHz
MIN
TYP
MAX
UNITS
Filter Gain, R = 229Ω
V
V = 3V
10.4
10.3
10.1
10.9
10.8
10.7
11.5
11.4
11.3
dB
dB
dB
IN
IN
P-P IN
S
V = 5V
S
V = 5V
S
Filter Gain Temperature Coefficient (Note 2)
f
= 260kHz, V = 2V
P-P
780
45
ppm/C
IN
IN
Noise
Noise BW = 10kHz to 5MHz, R = 806Ω
μV
RMS
IN
Distortion (Note 4)
1MHz, 2V , R = 800Ω
2nd Harmonic
3rd Harmonic
93
96
dBc
dBc
P-P
L
5MHz, 2V , R = 800Ω
2nd Harmonic
3rd Harmonic
66
73
dBc
dBc
P-P
L
l
l
Differential Output Swing
Measured Between Pins 4 and 5
Pin 7 Shorted to Pin 2
V = 5V
S
3.85
3.85
4.8
4.8
V
V
S
P-P DIFF
P-P DIFF
V = 3V
l
Input Bias Current
Average of Pin 1 and Pin 8
–70
–30
μA
l
l
l
Input Referred Differential Offset
R
IN
= 806Ω
V = 3V
5
10
8
25
30
35
mV
mV
mV
S
V = 5V
S
V = 5V
S
l
l
l
R
= 229Ω
V = 3V
5
5
5
13
16
20
mV
mV
mV
IN
S
V = 5V
S
V = 5V
S
Differential Offset Drift
10
μV/°C
l
l
l
Input Common Mode Voltage (Note 3)
Differential Input = 500mV
IN
,
V = 3V
0.0
0.0
–2.5
1.5
3.0
1.0
V
V
V
P-P
S
R
= 229Ω
V = 5V
S
V = 5V
S
l
l
l
Output Common Mode Voltage (Note 5)
Differential Output = 2V
Pin 7 at Midsupply
,
V = 3V
1.0
1.5
–2.5
1.5
3.0
2.0
V
V
V
P-P
S
V = 5V
S
V = 5V
S
l
l
l
Output Common Mode Offset
(with Respect to Pin 2)
V = 3V
–25
–30
–55
5
0
–5
50
45
35
mV
mV
mV
S
V = 5V
S
V = 5V
S
Common Mode Rejection Ratio
61
dB
l
l
Voltage at V
(Pin 7)
V = 5
S
2.46
4.3
2.51
1.5
2.55
7.7
V
V
MID
S
V = 3
V
V
Input Resistance
Bias Current
5.5
kꢀ
MID
l
l
V
OCM
= V
= V /2
V = 5
–15
–10
–3
–3
μA
μA
OCM
MID
S
S
V = 3
S
Power Supply Current
V = 3V, V = 5
28
31
34
38
mA
mA
mA
S
S
l
l
V = 3V, V = 5
S
S
V = 5V
30
S
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 5: Output common mode voltage is the average of the voltages at
Pins 4 and 5. The output common mode voltage is equal to the voltage
applied to Pin 2.
Note 6: The LT6600C is guaranteed functional over the operating
Note 2: This is the temperature coefficient of the internal feedback
temperature range –40°C to 85°C.
resistors assuming a temperature independent external resistor (R ).
Note 3: The input common mode voltage is the average of the voltages
IN
Note 7: The LT6600C is guaranteed to meet 0°C to 70°C specifications and
is designed, characterized and expected to meet the extended temperature
limits, but is not tested at –40°C and 85°C. The LT6600I is guaranteed to
meet specified performance from –40°C to 85°C.
applied to the external resistors (R ). Specification guaranteed for
IN
R
≥ 229ꢀ.
IN
Note 8: The inputs are protected by back-to-back diodes. If the differential
input voltage exceeds 1.4V, the input current should be limited to less than
10mA.
Note 4: Distortion is measured differentially using a differential stimulus.
The input common mode voltage, the voltage at Pin 2, and the voltage at
Pin 7 are equal to one half of the total power supply voltage.
66005fa
3
LT6600-5
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
Passband Gain and Delay
Passband Gain and Delay
1
0
13
12
11
10
9
120
110
100
90
120
110
100
90
10
0
V
= 5V
GAIN
S
GAIN
GAIN = 1
= 25°C
T
A
–1
–2
–3
–4
–5
–6
–7
–8
–9
–10
–20
–30
–40
–50
–60
–70
–80
80
80
DELAY
DELAY
70
70
8
60
60
7
50
50
6
40
40
5
GAIN = 1
GAIN = 4
30
30
4
T
= 25°C
T = 25°C
A
A
20
10
3
20
0
1
2
3
4
5
6
7
8
9
0
1
2
3
7
4
5
6
8
9
10
0.1
1
10
100
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
66005 G01
66005 G02
66005 G03
Output Impedance vs Frequency
Common Mode Rejection Ratio
Power Supply Rejection Ratio
100
10
1
90
80
70
60
50
40
30
80
70
60
50
40
30
20
10
0
V
= 5V
V
= 5V
S
S
GAIN = 1
= 25°C
GAIN = 1
= 1V
T
V
A
A
IN
P-P
T
= 25°C
V
V
= 3V
S
= 200mV
= 25°C
IN
P-P
T
A
+
V
TO DIFFOUT
0.1
0.1
1
10
100
0.01
0.1
1
10
100
0.01
0.1
1
10
100
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
66005 G04
66005 G05
66005 G06
Distortion vs Frequency
Distortion vs Frequency
Distortion vs Signal Level
–50
–60
–50
–40
–50
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
V
= 3V
= 800ꢀ
= 25°C
S
L
R
–60
–70
T
A
3RD HARMONIC,
5MHz INPUT
–60
–70
–70
2ND HARMONIC,
5MHz INPUT
–80
–80
–80
3RD HARMONIC,
1MHz INPUT
–90
–90
–90
–100
–110
–100
–110
–100
–110
2ND HARMONIC,
1MHz INPUT
V
= 3V, V = 2V
V = 5V, V = 2V
S IN P-P
S
L
IN
P-P
R
= 800ꢀ, T = 25°C
R = 800ꢀ, T = 25°C
L A
A
0
1
2
3
4
5
0.1
1
10
0.1
1
10
INPUT LEVEL (V
)
FREQUENCY (MHz)
FREQUENCY (MHz)
P-P
66005 G09
66005 G07
66005 G08
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4
LT6600-5
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Signal Level
Distortion vs Input Common Mode
Distortion vs Input Common Mode
–40
–50
–40
–50
–60
–70
–80
–40
–50
2ND HARMONIC,
2ND HARMONIC,
V
S
= 3V
V = 3V
S
3RD HARMONIC
5MHz INPUT
3RD HARMONIC,
= 3V
3RD HARMONIC,
V = 3V
S
V
S
2ND HARMONIC,
= 5V
2ND HARMONIC,
V = 5V
S
–60
–60
–70
2ND HARMONIC
5MHz INPUT
V
S
3RD HARMONIC,
= 5V
3RD HARMONIC,
= 5V
–70
V
V
S
S
3RD HARMONIC
1MHz INPUT
–80
–80
2ND HARMONIC
1MHz INPUT
–90
–90
–100
–110
–90
GAIN = 4, PIN 7 = V /2
GAIN = 1, PIN 7 = V /2
S
–100
–110
–100
–110
S
V
=
5V
2V 1MHz INPUT
P-P
S
L
2V 1MHz INPUT
P-P
R
= 800ꢀ, T = 25°C
R = 800ꢀ, T = 25°C
L A
A
R
L
= 800ꢀ, T = 25°C
A
1
2
3
5
–3
–2
–1
0
1
2
3
–3
–1
0
1
2
3
0
4
–2
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
66005 G12
INPUT LEVEL (V
)
P-P
66005 G10
66005 G11
Transient Response, Differential
Gain = 1, Single-Ended Input,
Differential Output
Power Supply Current
vs Power Supply Voltage
Distortion vs Temperature
20
0
36
34
32
30
28
26
24
1dB PASSBAND GAIN
COMPRESSION POINTS
1MHz T = 25°C
A
–
OUT
200mV/DIV
1MHz T = 85°C
A
T
= 85°C
A
3RD HARMONIC
= 85°C
–20
–40
–60
–80
–100
–120
T
A
+
OUT
3RD HARMONIC
= 25°C
T
= 25°C
A
200mV/DIV
T
A
–
T
= –40°C
A
2ND HARMONIC
IN
T
A
= 85°C
500mV/DIV
+
IN
22
20
2ND HARMONIC
T
= 25°C
A
4
6
7
100ns/DIV
0
1
2
3
5
6
2
4
8
10
12
1MHz INPUT LEVEL (V
)
TOTAL SUPPLY VOLTAGE (V)
P-P
66005 G15
66005 G13
66005 G14
Distortion
vs Output Common Mode
Input Referred Noise
–40
–50
–60
45
40
35
30
25
20
15
10
5
90
80
70
60
50
40
30
20
10
0
GAIN = 4
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
PIN 7 = V /2
S
T
= 25°C
P-P
= 800ꢀ
A
0.5V 1MHz INPUT
R
L
2ND HARMONIC, V = 3V
S
3RD HARMONIC, V = 3V
S
–70
–80
2ND HARMONIC, V = 5V
S
3RD HARMONIC, V = 5V
S
S
S
2ND HARMONIC, V
3RD HARMONIC, V
=
=
5V
5V
–90
–100
–110
0
0.01
–1.5 –1.0
0
0.5 1.0 1.5 2.0 2.5
–0.5
0.1
10
100
VOLTAGE PIN 2 TO PIN 7 (V)
FREQUENCY (MHz)
66005 G16
66005 G17
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5
LT6600-5
PIN FUNCTIONS
–
+
IN and IN (Pins 1, 8): Input Pins. Signals can be ap-
should be as close as possible to the IC. For dual supply
applications, bypass Pin 3 to ground and Pin 6 to ground
with a quality 0.1μF ceramic capacitor.
plied to either or both input pins through identical external
resistors, R . The DC gain from differential inputs to the
IN
differential outputs is 806Ω/R .
+
–
IN
OUT and OUT (Pins 4, 5): Output Pins. Pins 4 and 5 are
the filter differential outputs. Each pin can drive a 100Ω
and/or 50pF load to AC ground.
V
OCM
(Pin 2): Is the DC Common Mode Reference Voltage
for the 2nd Filter Stage. Its value programs the common
modevoltageofthedifferentialoutputofthefilter.Pin2isa
highimpedanceinput,whichcanbedrivenfromanexternal
voltage reference, or Pin 2 can be tied to Pin 7 on the PC
board. Pin 2 should be bypassed with a 0.01μF ceramic
capacitor unless it is connected to a ground plane.
V
(Pin 7): The V
pin is internally biased at mid-
MID
MID
supply, see block diagram. For single supply operation
the V pin should be bypassed with a quality 0.01μF
MID
ceramic capacitor to Pin 6. For dual supply operation,
Pin 7 can be bypassed or connected to a high quality DC
ground. A ground plane should be used. A poor ground
will increase noise and distortion. Pin 7 sets the output
common mode voltage of the 1st stage of the filter. It has
a 5.5kΩ impedance, and it can be overridden with an
external low impedance voltage source.
+
–
V and V (Pins 3, 6): Power Supply Pins. For a single
3.3Vor5Vsupply(Pin6grounded)aquality0.1μFceramic
bypass capacitor is required from the positive supply pin
(Pin 3) to the negative supply pin (Pin 6). The bypass
BLOCK DIAGRAM
R
IN
+
+
–
–
V
IN
V
OUT
5
V
IN
MID
8
7
6
+
V
11k
11k
PROPRIETARY
LOWPASS
806ꢀ
FILTER STAGE
400ꢀ
–
V
OP AMP
400ꢀ
400ꢀ
+
+
OCM
–
–
V
V
OCM
+
+
–
–
400ꢀ
806ꢀ
1
2
3
4
66005 BD
+
–
–
+
V
V
IN
IN
OCM
V
OUT
R
IN
66005fa
6
LT6600-5
APPLICATIONS INFORMATION
Interfacing to the LT6600-5
is 2V for frequencies below 5MHz. The common mode
P-P
output voltage is determined by the voltage at Pin 2. Since
Pin 2 is shorted to Pin 7, the output common mode is the
mid-supply voltage. In addition, the common mode input
voltage can be equal to the mid-supply voltage of Pin 7
(refer to the Distortion vs Input Common Mode Level
graphs in the Typical Performance Characteristics).
The LT6600-5 requires 2 equal external resistors, R , to
IN
set the differential gain to 806Ω/R . The inputs to the
IN
+
–
filter are the voltages V and V presented to these
IN
IN
external components, Figure 1. The difference between
+
–
V
and V is the differential input voltage. The aver-
IN
IN
+
–
age of V and V
Similarly,thevoltagesV
is the common mode input voltage.
IN
IN
+
–
andV
appearingatPins4
Figure2showshowtoACcouplesignalsintotheLT6600-5.
In this instance, the input is a single-ended signal. AC
coupling allows the processing of single-ended or dif-
ferential signals with arbitrary common mode levels. The
0.1μFcouplingcapacitorandthe806Ωgainsettingresistor
form a high pass filter, attenuating signals below 2kHz.
Larger values of coupling capacitors will proportionally
reduce this highpass 3dB frequency.
OUT
OUT
and 5 of the LT6600-5 are the filter outputs. The differ-
+
–
ence between V
and V
is the differential output
OUT
OUT
+
–
voltage. The average of V
mode output voltage.
and V
is the common
OUT
OUT
Figure 1 illustrates the LT6600-5 operating with a single
3.3V supply and unity passband gain; the input signal is
DC coupled. The common mode input voltage is 0.5V and
the differential input voltage is 2V . The common mode
In Figure 3 the LT6600-5 is providing 12dB of gain. The
gain resistor has an optional 62pF in parallel to improve
P-P
output voltage is 1.65V and the differential output voltage
3.3V
0.1μF
V
V
3
–
806ꢀ
3
2
1
0
3
2
1
0
1
7
2
8
–
+
V
V
4
IN
+
–
+
–
V
V
+
OUT
V
OUT
LT6600-5
+
V
0.01μF
IN
V
OUT
–
OUT
5
+
IN
806ꢀ
6
t
t
–
66005 F01
V
IN
Figure 1
3.3V
3
0.1μF
4
V
V
0.1μF
0.1μF
806ꢀ
806ꢀ
1
3
2
1
0
2
1
–
+
–
+
V
V
+
7
OUT
V
V
OUT
LT6600-5
2
8
+
–
V
IN
0.01μF
OUT
–
0
t
+
OUT
5
V
+
IN
6
–1
66005 F02
Figure 2
62pF
5V
0.1μF
4
V
V
3
200ꢀ
1
7
2
8
–
3
3
V
V
–
IN
IN
+
+
–
V
V
OUT
+
OUT
LT6600-5
2
1
0
2
1
V
0.01μF
OUT
–
V
OUT
500mV (DIFF)
P-P
–
+
5
+
+
V
V
200ꢀ
62pF
IN
6
t
t
0
+
–
2V
66005 F03
IN
–
0.01μF
Figure 3
66005fa
7
LT6600-5
APPLICATIONS INFORMATION
the passband flatness near 5MHz. The common mode
output voltage is set to 2V.
Figure5isalaboratorysetupthatcanbeusedtocharacter-
izetheLT6600-5usingsingle-endedinstrumentswith50Ω
source impedance and 50Ω input impedance. For a unity
gain configuration the LT6600-5 requires a 806Ω source
resistance yet the network analyzer output is calibrated
for a 50Ω load resistance. The 1:1 transformer, 51.1Ω
and 787Ω resistors satisfy the two constraints above.
The transformer converts the single-ended source into a
differential stimulus. Similarly, the output the LT6600-5
will have lower distortion with larger load resistance yet
the analyzer input is typically 50Ω. The 4:1 turns (16:1
impedance) transformer and the two 402Ω resistors of
Figure 5, present the output of the LT6600-5 with a 1600Ω
differential load, or the equivalent of 800Ω to ground at
each output. The impedance seen by the network analyzer
input is still 50Ω, reducing reflections in the cabling be-
tween the transformer and analyzer input.
Use Figure 4 to determine the interface between the
LT6600-5 and a current output DAC. The gain, or “tran-
simpedance,” is defined as A = V /I Ω. To compute
OUT IN
the transimpedance, use the following equation:
806 •R1
R1+R2
A =
Ω
By setting R1 + R2 = 806Ω, the gain equation reduces
to A = R1Ω.
The voltage at the pins of the DAC is determined by R1,
R2, the voltage on Pin 7 and the DAC output current
(IIN+ or IIN–). Consider Figure 4 with R1 = 49.9Ω and R2
= 750Ω. The voltage at Pin 7 is 1.65V. The voltage at the
DAC pins is given by:
2.5V
R1
R1+R2+806 IN R1+R2
= 51mV +I 46.8Ω
R1•R2
0.1μF
V
DAC = VPIN7
•
+I
COILCRAFT
TTWB-16A
4:1
COILCRAFT
TTWB-1010
NETWORK
ANALYZER
SOURCE
NETWORK
ANALYZER
INPUT
3
IN
787ꢀ
1:1
1
7
2
8
402ꢀ
–
4
+
–
+
50ꢀ
I is IIN or IIN . The transimpedance in this example is
LT6600-5
IN
51.1ꢀ
50ꢀ
402ꢀ
50.3Ω.
–
5
+
787ꢀ
6
0.1μF
66005 F05
CURRENT
3.3V
OUTPUT
0.1μF
DAC
–2.5V
–
+
3
R2
I
I
IN
IN
1
7
2
8
–
4
+
–
Figure 5
+
V
V
OUT
R1
R1
0.01μF
R2
LT6600-5
Differential and Common Mode Voltage Ranges
–
OUT
5
+
The differential amplifiers inside the LT6600-5 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the filter. This limiting function prevents
excessive power dissipation in the internal circuitry and
provides output short-circuit protection. The limiting
function begins to take effect at output signal levels above
6
66005 F04
Figure 4
Evaluating the LT6600-5
2V and it becomes noticeable above 3.5V . This is
P-P
P-P
The low impedance levels and high frequency operation
of the LT6600-5 require some attention to the matching
networks between the LT6600-5 and other devices. The
previous examples assume an ideal (0Ω) source imped-
ance and a large (1kΩ) load resistance. Among practi-
cal examples where impedance must be considered is
the evaluation of the LT6600-5 with a network analyzer.
illustrated in Figure 6; the LTC6600-5 was configured with
unity passband gain and the input of the filter was driven
with a 1MHz signal. Because this voltage limiting takes
place well before the output stage of the filter reaches the
supply rails, the input/output behavior of the IC shown
in Figure 6 is relatively independent of the power supply
voltage.
66005fa
8
LT6600-5
APPLICATIONS INFORMATION
20
the power supply level and gain setting (see “Electrical
Characteristics”).
1dB PASSBAND GAIN
COMPRESSION POINTS
1MHz T = 25°C
A
0
–20
1MHz T = 85°C
A
3RD HARMONIC
= 85°C
Common Mode DC Currents
T
A
3RD HARMONIC
= 25°C
–40
T
InapplicationslikeFigure1andFigure3wheretheLT6600-5
not only provides lowpass filtering but also level shifts the
common mode voltage of the input signal, DC currents
will be generated through the DC path between input and
output terminals. Minimize these currents to decrease
power dissipation and distortion.
A
–60
–80
2ND HARMONIC
A
T
= 85°C
–100
–120
2ND HARMONIC
= 25°C
T
A
4
6
7
0
1
2
3
5
1MHz INPUT LEVEL (V
)
P-P
Consider the application in Figure 3. Pin 7 sets the output
commonmodevoltageofthe1stdifferentialamplifierinside
the LT6600-5 (see the “Block Diagram” section) at 2.5V.
Since the input common mode voltage is near 0V, there
will be approximately a total of 2.5V drop across the series
combinationoftheinternal806Ωfeedbackresistorandthe
external200Ωinputresistor.Theresulting2.5mAcommon
mode DC current in each input path, must be absorbed by
66005 F06
Figure 6
The two amplifiers inside the LT6600-5 have independent
control of their output common mode voltage (see the
“block diagram” section). The following guidelines will
optimize the performance of the filter for single supply
operation.
+
–
the sources V and V . Pin 2 sets the common mode
Pin 7 must be bypassed to an AC ground with a 0.01μF or
highercapacitor.Pin7canbedrivenfromalowimpedance
source, provided it remains at least 1.5V above V and at
least 1.5V below V . An internal resistor divider sets the
voltage of Pin 7. While the internal 11k resistors are well
matched, their absolute value can vary by 20%. This
should be taken into consideration when connecting an
external resistor network to alter the voltage of Pin 7.
IN
IN
output voltage of the 2nd differential amplifier inside the
LT6600-5, and therefore sets the common mode output
voltage of the filter. Since in the example, Figure 3, Pin 2
differsfromPin7by0.5V, anadditional1.25mA(0.625mA
per side) of DC current will flow in the resistors coupling
the 1st differential amplifier output stage to filter output.
Thus, a total of 6.25mA is used to translate the common
mode voltages.
–
+
Pin 2 can be shorted to Pin 7 for simplicity. If a different
common mode output voltage is required, connect Pin 2
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at Pin 2 must be less than or equal to
the mid-supply level. For example, voltage (Pin 2) ≤1.65V
on a single 3.3V supply. For power supply voltages higher
than3.3VthevoltageatPin2canbesetabovemid-supply.
The voltage on Pin 2 should not be more than 1V below
the voltage on Pin 7. The voltage on Pin 2 should not be
more than 2V above the voltage on Pin 7. Pin 2 is a high
impedance input.
A simple modification to Figure 3 will reduce the DC com-
monmodecurrentsby36%.IfPin7isshortedtoPin2,the
common mode output voltage of both op amp stages will
be 2V and the resulting DC current will be 4mA. Of course,
by AC coupling the inputs of Figure 3 and shorting Pin 7
to Pin 2, the common mode DC current is eliminated.
Noise
The noise performance of the LT6600-5 can be evaluated
with the circuit of Figure 7.
The LT6600-5 was designed to process a variety of input
signals including signals centered around the mid-sup-
ply voltage and signals that swing between ground and
a positive voltage in a single supply system (Figure 1).
The range of allowable input common mode voltage (the
Given the low noise output of the LT6600-5 and the 6dB
attenuation of the transformer coupling network, it will
be necessary to measure the noise floor of the spectrum
analyzer and subtract the instrument noise from the filter
noise measurement.
+
–
average of V and V
in Figure 1) is determined by
IN
IN
66005fa
9
LT6600-5
APPLICATIONS INFORMATION
45
40
35
30
25
20
15
10
5
90
80
70
60
50
40
30
20
10
0
2.5V
INTEGRATED NOISE, GAIN = 1X
INTEGRATED NOISE, GAIN = 4X
NOISE DENSITY, GAIN = 1X
NOISE DENSITY, GAIN = 4X
0.1μF
SPECTRUM
COILCRAFT
ANALYZER
R
3
TTWB-1010
1:1
IN
V
IN
INPUT
1
7
2
8
25ꢀ
25ꢀ
–
4
+
LT6600-5
50ꢀ
–
5
+
0.1μF
R
IN
6
66005 F07
–2.5V
0
0.01
0.1
10
100
Figure 7
FREQUENCY (MHz)
66005 G08
Example: With the IC removed and the 25Ω resistors
Figure 8
grounded, measure the total integrated noise (e ) of the
S
Conversely,ifeachoutputismeasuredindividuallyandthe
noise power added together, the resulting calculated noise
level will be higher than the true differential noise.
spectrum analyzer from 10kHz to 5MHz. With the IC in-
serted, thesignalsource(V )disconnected, andtheinput
IN
resistors grounded, measure the total integrated noise
out of the filter (e ). With the signal source connected,
O
Power Dissipation
set the frequency to 1MHz and adjust the amplitude until
V measures 100mV . Measure the output amplitude,
IN
OUT
P-P
The LT6600-5 amplifiers combine high speed with large-
signal currents in a small package. There is a need to
ensure that the dies’s junction temperature does not
exceed 150°C. The LT6600-5 package has Pin 6 fused
to the lead frame to enhance thermal conduction when
connecting to a ground plane or a large metal trace. Metal
trace and plated through-holes can be used to spread the
heat generated by the device to the backside of the PC
board. For example, on a 3/32" FR-4 board with 2oz cop-
per, a total of 660 square millimeters connected to Pin 6
of the LT6600-5 (330 square millimeters on each side of
V
, and compute the passband gain A = V /V . Now
OUT IN
compute the input referred integrated noise (e ) as:
IN
(eO)2 –(eS)2
eIN =
A
Table 1 lists the typical input referred integrated noise for
various values of R .
IN
Figure 8 is plot of the noise spectral density as a function
of frequency for an LT6600-5 with R = 806Ω and 200Ω
IN
the PC board) will result in a thermal resistance, θ , of
JA
using the fixture of Figure 7 (the instrument noise has
about 85°C/W. Without extra metal trace connected to the
been subtracted from the results).
–
V pin to provide a heat sink, the thermal resistance will
Table 1. Noise Performance
INPUT REFERRED
be around 105°C/W. Table 2 can be used as a guide when
considering thermal resistance.
PASSBAND
GAIN (V/V)
INTEGRATED NOISE INPUT REFERRED
R
10kHz TO 10MHz
NOISE dBm/Hz
IN
Table 2. LT6600-5 SO-8 Package Thermal Resistance
COPPER AREA
4
2
1
200Ω
402Ω
806Ω
24μV
38μV
69μV
–149
RMS
RMS
RMS
–145
TOPSIDE
BACKSIDE BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2
2
2
(mm )
(mm )
(mm )
–140
1100
330
35
1100
330
35
2500
2500
2500
2500
2500
65°C/W
85°C/W
95°C/W
100°C/W
105°C/W
The noise at each output is comprised of a differential
component and a common mode component. Using a
transformerorcombinertoconvertthedifferentialoutputs
tosingle-endedsignalrejectsthecommonmodenoiseand
gives a true measure of the S/N achievable in the system.
35
0
0
0
66005fa
10
LT6600-5
APPLICATIONS INFORMATION
Junction temperature, T , is calculated from the ambient
ent temperature is maximum. To compute the junction
temperature, measure the supply current under these
worst-case conditions, estimate the thermal resistance
from Table 2, then apply the equation for TJ. For example,
using the circuit in Figure 3 with DC differential input volt-
age of 250mV, a differential output voltage of 1V, 1kΩ load
resistanceandanambienttemperatureof85°C,thesupply
current (current into Pin 3) measures 32.2mA. Assuming
a PC board layout with a 35mm2 copper trace, the θJA is
100°C/W. The resulting junction temperature is:
J
temperature, T , and power dissipation, P . The power
A
D
dissipation is the product of supply voltage, V , and
S
supply current, I . Therefore, the junction temperature
S
is given by:
T = T + (P • θ ) = T + (V • I • θ )
J
A
D
JA
A
S
S
JA
where the supply current, I , is a function of signal level,
S
load impedance, temperature and common mode volt-
ages.
For a given supply voltage, the worst-case power dis-
sipation occurs when the differential input signal is
maximum, the common mode currents are maximum
(see Applications Information regarding common mode
DC currents), the load impedance is small and the ambi-
T = T + (P • θ ) = 85 + (5 • 0.0322 • 100) = 101°C
J
A
D
JA
When using higher supply voltages or when driving small
impedances, more copper may be necessary to keep T
below 150°C.
J
PACKAGE DESCRIPTION
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 – .197
(4.801 – 5.004)
.045 ±.005
NOTE 3
.050 BSC
7
5
8
6
.245
MIN
.160 ±.005
.150 – .157
(3.810 – 3.988)
NOTE 3
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
1
3
4
2
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
(0.254 – 0.508)
× 45°
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
.008 – .010
(0.203 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
.050
(1.270)
BSC
.014 – .019
(0.355 – 0.483)
TYP
NOTE:
INCHES
1. DIMENSIONS IN
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
SO8 0303
66005fa
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT6600-5
TYPICAL APPLICATION
Dual, Matched, 6th Order, 5MHz Lowpass Filter
Single-Ended Input (IIN and QIN) and Differential Output (IOUT and QOUT
)
+
V
I
0.1μF
IN
+
0.1μF
V
806ꢀ
806ꢀ
3
1
4
–
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
+
+
+
7
2
8
V
V
LT1568
LT6600-5
249ꢀ
249ꢀ
249ꢀ
249ꢀ
249ꢀ
249ꢀ
I
OUT
Q
INVA
INVB
IN
–
6
+
SA
SB
5
0.1μF
OUTA OUTB
OUTA OUTB
GNDA GNDB
–
V
I
Q
OUT
Q
IN
OUT
+
V
0.1μF
4
GAIN =
OR
= 1
NC
–
EN
–
I
IN
V
V
806ꢀ
3
1
0.1μF
–
+
7
2
8
LT6600-5
–
Q
V
OUT
–
6
+
5
806ꢀ
0.1μF
66005 TA02
–
V
Amplitude Response
Transient Response
12
0
OUTPUT
OR Q
–12
–24
–36
–48
–60
–72
–84
–96
–108
(I
OUT
)
OUT
200mV/DIV
INPUT
(I OR Q
IN IN
)
500mV/DIV
66005 TA02c
100ns/DIV
100
1
10
40
FREQUENCY (Hz)
66005 TA02b
RELATED PARTS
PART NUMBER
LTC®1565-31
LTC1566-1
LT1567
DESCRIPTION
COMMENTS
650kHz Linear Phase Lowpass Filter
Low Noise, 2.3MHz Lowpass Filter
Continuous Time, SO8 Package, Fully Differential
Continuous Time, SO8 Package, Fully Differential
1.4nV/√Hz Op Amp, MSOP Package, Differential Output
Very Low Noise, High Frequency Filter Building Block
Very Low Noise, 4th Order Building Block
LT1568
Lowpass and Bandpass Filter Designs Up to 10MHz,
Differential Outputs
LTC1569-7
LT6600-2.5
LT6600-10
LT6600-20
Linear Phase, DC Accurate, Tunable 10th Order Lowpass One External Resistor Sets Filter Cutoff Frequency, Differential Inputs
Filter
Very Low Noise, Differential Amplifier
and 2.5MHz Lowpass Filter
Adjustable Output Common Mode Voltage
Adjustable Output Common Mode Output Voltage
Adjustable Output Common Mode Voltage
Very Low Noise, Differential Amplifier
and 10MHz Lowpass Filter
Very Low Noise, Differential Amplifier
and 20MHz Lowpass Filter
66005fa
LT 0408 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
© LINEAR TECHNOLOGY CORPORATION 2004
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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