LT6600-20
Very Low Noise, Differential
Amplifier and 20MHz Lowpass Filter
FEATURES
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DESCRIPTION
The LT
®
6600-20 combines a fully differential amplifier with a
4th order 20MHz lowpass filter approximating a Chebyshev
frequency response. Most differential amplifiers require
many precision external components to tailor gain and
bandwidth. In contrast, with the LT6600-20, two external
resistors program differential gain, and the filter’s 20MHz
cutoff frequency and passband ripple are internally set.
The LT6600-20 also provides the necessary level shifting
to set its output common mode voltage to accommodate
the reference voltage requirements of A/Ds.
Using a proprietary internal architecture, the LT6600-20
integrates an antialiasing filter and a differential ampli-
fier/driver without compromising distortion or low noise
performance. At unity gain the measured in band signal-
to-noise ratio is an impressive 76dB. 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.
The LT6600-20 also features low voltage operation. The
differential design provides outstanding performance for
a 2V
P-P
signal level while the part operates with a single
3V supply.
The LT6600-20 is packaged in an SO-8 and is pin compat-
ible with stand alone differential amplifiers.
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Programmable Differential Gain via Two External
Resistors
Adjustable Output Common Mode Voltage
Operates and Specified with 3V, 5V, ±5V Supplies
0.5dB Ripple 4th Order Lowpass Filter with 20MHz
Cutoff
76dB S/N with 3V Supply and 2V
P-P
Output
Low Distortion, 2V
P-P
, 800Ω Load
2.5MHz: 83dBc 2nd, 88dBc 3rd
20MHz: 63dBc 2nd, 64dBc 3rd
Fully Differential Inputs and Outputs
SO-8 Package
Compatible with Popular Differential Amplifier
Pinouts
APPLICATIONS
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High Speed ADC Antialiasing and DAC Smoothing in
Networking or Cellular Base Station Applications
High Speed Test and Measurement Equipment
Medical Imaging
Drop-in Replacement for Differential Amplifiers
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
LT6600-20
5V
0.1μF
R
IN
402Ω 1
7
0.01μF
V
IN
R
IN
402Ω
2
8
3
A/D
LTC1748
AMPLITUDE (dB)
5V
V
+
D
OUT
V
CM
1μF
GAIN = 402Ω/R
IN
66002 TA01a
An 8192 Point FFT Spectrum
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
10
20
FREQUENCY (MHz)
66002 TA01b
INPUT 5.9MHz
2V
P-P
f
SAMPLE
= 80MHz
–
V
MID
V
OCM
+
–
4
49.9Ω
18pF
+
A
IN
49.9Ω
5
+
6
–
V
–
30
40
66002fb
1
LT6600-20
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
IN
–
1
V
OCM
2
V
+
3
OUT
+
4
8
7
6
5
IN
+
V
MID
V
–
OUT
–
Total Supply Voltage .................................................11V
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
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 100°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT6600CS8-20#PBF
LT6600IS8-20#PBF
LEAD BASED FINISH
LT6600CS8-20
LT6600IS8-20
TAPE AND REEL
LT6600CS8-20#TRPBF
LT6600IS8-20#TRPBF
TAPE AND REEL
LT6600CS8-20#TR
LT6600IS8-20#TR
PART MARKING
660020
600I20
PART MARKING
660020
600I20
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–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/
The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. Unless otherwise specified V
S
= 5V (V
+
= 5V, V
–
= 0V), R
IN
= 402Ω, and R
LOAD
= 1k.
PARAMETER
Filter Gain, V
S
= 3V
CONDITIONS
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= 2MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 10MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 16MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 20MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 60MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 100MHz (Gain Relative to 260kHz)
Filter Gain, V
S
= 5V
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= 2MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 10MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 16MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 20MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 60MHz (Gain Relative to 260kHz)
V
IN
= 2V
P-P
, f
IN
= 100MHz (Gain Relative to 260kHz)
Filter Gain, V
S
= ±5V
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
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ELECTRICAL CHARACTERISTICS
MIN
–0.4
–0.1
–0.2
–0.1
–0.8
TYP
0.1
0
0.1
0.5
0
–33
–50
MAX
0.5
0.1
0.5
1.9
1
–28
0.5
0.1
0.4
1.6
0.6
–28
0.4
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
66002fb
–0.5
–0.1
–0.2
–0.3
–1.3
0
0
0.1
0.4
–0.4
–33
–50
–0.6
–0.1
2
LT6600-20
ELECTRICAL CHARACTERISTICS
PARAMETER
Filter Gain, R
IN
= 100
CONDITIONS
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= 3V
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= 5V
V
IN
= 0.5V
P-P
, f
IN
= DC to 260kHz, V
S
= 5V
f
IN
= 250kHz, V
IN
= 2V
P-P
Noise BW = 10kHz to 20MHz
2.5MHz, 2V
P-P
, R
L
= 800Ω
20MHz, 2V
P-P
, R
L
= 800Ω
Differential Output Swing
Input Bias Current
Input Referred Differential Offset
Measured Between Pins 4 and 5
Average of Pin 1 and Pin 8
R
IN
= 402Ω
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 3V
V
S
= 5V
V
S
= ±5V
V
S
= 5
V
S
= 3
V
OCM
= V
MID
= V
S
/2
V
S
= 5V
V
S
= 3V
V
S
= 3V, V
S
= 5
V
S
= 3V, V
S
= 5
V
S
= ±5V
2nd Harmonic
3rd Harmonic
2nd Harmonic
3rd Harmonic
V
S
= 5V
V
S
= 3V
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The
l
denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. Unless otherwise specified V
S
= 5V (V
+
= 5V, V
–
= 0V), R
IN
= 402Ω, and R
LOAD
= 1k.
MIN
11.6
11.5
11.4
TYP
12.1
12.0
11.9
780
118
83
88
63
64
3.80
3.75
–95
4.75
4.50
–50
5
10
10
5
5
5
10
Differential Input = 500mV
P-P
,
R
IN
= 100Ω
Differential Input = 2V
P-P
,
Pin 7 = OPEN
Common Mode Voltage at Pin 2
0.0
0.0
–2.5
1.0
1.5
–1.0
–35
–40
–55
2.46
4.35
–15
–10
5
0
–5
66
2.51
1.5
5.7
–3
–3
42
46
46
53
56
2.55
7.65
1.5
3.0
1.0
1.5
3.0
2.0
40
40
35
25
30
35
15
17
20
MAX
12.6
12.5
12.4
UNITS
dB
dB
dB
ppm/C
μV
RMS
dBc
dBc
dBc
dBc
V
P-P DIFF
V
P-P DIFF
μA
mV
mV
mV
mV
mV
mV
μV/°C
V
V
V
V
V
V
mV
mV
mV
dB
V
V
kΩ
μA
μA
mA
mA
mA
Filter Gain Temperature Coefficient (Note 2)
Noise
Distortion (Note 4)
R
IN
= 100Ω
Differential Offset Drift
Input Common Mode Voltage (Note 3)
Output Common Mode Voltage (Note 5)
Output Common Mode Offset
(with Respect to Pin 2)
Common Mode Rejection Ratio
Voltage at V
MID
(Pin 7)
V
MID
Input Resistance
V
OCM
Bias Current
Power Supply Current
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 2:
This is the temperature coefficient of the internal feedback
resistors assuming a temperature independent external resistor (R
IN
).
Note 3:
The input common mode voltage is the average of the voltages
applied to the external resistors (R
IN
). Specification guaranteed for R
IN
≥
100Ω.
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.
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-20 is guaranteed functional over the operating
temperature range –40°C to 85°C.
Note 7:
The LT6600C-20 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-20 is
guaranteed to meet specified performance from –40°C to 85°C.
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.
66002fb
3
LT6600-20
TYPICAL PERFORMANCE CHARACTERISTICS
Amplitude Response
10
0
–10
–20
GAIN (dB)
GAIN (dB)
–30
–40
–50
–60
–70
–80
V
S
= 5V
GAIN = 1
T
A
= 25°C
1
10
FREQUENCY (MHz)
100
66002 G01
Passband Gain and Phase
2
0
–2
–4
–6
–8
–10
–12
–14
–16
–18
0.5
6.5
18.5
24.5
12.5
FREQUENCY (MHz)
PHASE
GAIN
V
S
= 5V
GAIN = 1
T
A
= 25°C
95
50
5
–40
PHASE (DEG)
–85
–130
–175
–220
–265
–310
–355
30.5
66002 G02
–90
0.1
Passband Gain and Group Delay
2
0
–2
–4
GAIN (dB)
–6
–8
–10
–12
–14
–16
–18
0.5
6.5
18.5
24.5
12.5
FREQUENCY (MHz)
GROUP
DELAY
GAIN
V
S
= 5V
GAIN = 1
T
A
= 25°C
50
45
40
35
30
25
20
15
10
5
0
30.5
66002 G03
Passband Gain and Group Delay
14
12
10
8
GAIN (dB)
6
4
2
0
–2
–4
–6
0.5
6.5
18.5
24.5
12.5
FREQUENCY (MHz)
GROUP
DELAY
GROUP DELAY (ns)
GAIN
V
S
= 5V
GAIN = 4
T
A
= 25°C
50
45
OUTPUT IMPEDANCE (Ω)
40
35
30
25
20
15
10
5
0
30.5
66002 G04
Output Impedance
100
V
S
= 5V
GAIN = 1
T
A
= 25°C
GROUP DELAY (ns)
10
1
0.1
0.1
1
10
FREQUENCY (MHz)
100
66002 G05
Common Mode Rejection Ratio
80
75
70
65
CMRR (dB)
PSRR (dB)
60
55
50
45
40
35
30
0.1
1
10
FREQUENCY (MHz)
100
66002 G06
Power Supply Rejection Ratio
100
90
80
70
60
50
40
30
20
10
0
0.001
–100
0.01
0.1
1
FREQUENCY (MHz)
10
100
66002 G07
Distortion vs Frequency
–40
–50
DISTORTION (dB)
–60
–70
–80
–90
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
INPUT = 1V
P-P
V
S
= 5V
GAIN = 1
T
A
= 25°C
V
+
TO DIFFOUT
V
S
= 3V
T
A
= 25°C
V
IN
= 2V
P-P
V
S
= 3V
R
L
= 800Ω AT
EACH OUTPUT
GAIN = 1
T
A
= 25°C
0.1
1
10
FREQUENCY (MHz)
100
66002 G08
66002fb
4
LT6600-20
TYPICAL PERFORMANCE CHARACTERISTICS
Distortion
vs Signal Level, V
S
= 3V
–40
–50
DISTORTION (dB)
–60
–70
–80
–90
–100
0
1
2
3
INPUT LEVEL (V
P-P
)
4
5
66002 G09
Distortion
vs Signal Level, V
S
= ±5V
–40
–50
DISTORTION (dB)
–60
–70
–80
–90
–100
0
1
2ND HARMONIC,
10MHz INPUT
3RD HARMONIC,
10MHz INPUT
2ND HARMONIC,
1MHz INPUT
3RD HARMONIC,
1MHz INPUT
–40
DISTORTION COMPONENT (dB)
–50
–60
–70
–80
–90
Distortion
vs Input Common Mode Level
2ND HARMONIC,
V
S
= 3V
3RD HARMONIC,
V
S
= 3V
2ND HARMONIC,
V
S
= 5V
3RD HARMONIC,
V
S
= 5V
2V
P-P
1MHz INPUT
R
L
= 800Ω AT
EACH OUTPUT
GAIN = 1
T
A
= 25°C
3RD HARMONIC
V
S
= 3V
10MHz INPUT
R
L
= 800Ω AT
EACH OUTPUT
GAIN = 1
2ND
T
A
= 25°C
HARMONIC
10MHz INPUT
3RD
HARMONIC
1MHz INPUT
2ND HARMONIC
1MHz INPUT
V
S
= ±5V
R
L
= 800Ω AT
EACH OUTPUT
GAIN = 1
T
A
= 25°C
2
3
INPUT LEVEL (V
P-P
)
4
5
66002 G10
–100
–3
3
–2
–1
0
1
2
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
66002 G11
Distortion
vs Input Common Mode Level
–40
DISTORTION COMPONENT (dB)
–50
–60
–70
–80
–90
500mV
P-P
1MHz INPUT, GAIN = 4,
R
L
= 800Ω AT EACH OUTPUT
–3
3
–2
–1
0
1
2
INPUT COMMON MODE VOLTAGE
RELATIVE TO PIN 7 (V)
66002 G12
2ND HARMONIC,
V
S
= 3V
3RD HARMONIC,
V
S
= 3V
2ND HARMONIC,
V
S
= 5V
3RD HARMONIC,
V
S
= 5V
–40
DISTORTION COMPONENT (dB)
–50
–60
–70
–80
–90
–100
–110
Distortion
vs Output Common Mode
2ND HARMONIC,
V
S
= 3V
3RD HARMONIC,
V
S
= 3V
2ND HARMONIC,
V
S
= 5V
3RD HARMONIC,
V
S
= 5V
2ND HARMONIC,
V
S
= ±5V
3RD HARMONIC,
V
S
= ±5V
–100
2V
P-P
1MHz INPUT, GAIN = 1,
R
L
= 800Ω AT EACH OUTPUT
–2 –1.5 –1 –0.5 0 0.5 1 1.5
VOLTAGE PIN 2 TO PIN 7 (V)
2
66002 G13
Total Supply Current
vs Total Supply Voltage
60
TOTAL SUPPLY CURRENT (mA)
50
40
30
20
10
0
0
1
2 3 4 5 6 7 8
TOTAL SUPPLY VOLTAGE (V)
9
10
T
A
= 85°C
T
A
= 25°C
T
A
= –40°C
DIFFERENTIAL
INPUT
200mV/DIV
V
OUT
+
50mV/DIV
Transient Response, Gain = 1
100ns/DIV
66002 G15
66002 G14
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