LT6600-20
Very Low Noise, Differential
Amplifier and 20MHz Lowpass Filter
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
s
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
The LT
®
6600-20 combines a fully differential amplifier
with a 4th order 20MHz lowpass filter approximating a
Chebyshev frequency response. Most differential amplifi-
ers 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 accom-
modate the reference voltage requirements of A/Ds.
Using a proprietary internal architecture, the LT6600-20
integrates an antialiasing filter and a differential amplifier/
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 signifi-
cantly 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.
APPLICATIO S
s
s
s
s
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
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
LT6600-20
5V
0.1µF
R
IN
402Ω 1
7
0.01µF
V
IN
R
IN
402Ω
2
8
3
An 8192 Point FFT Spectrum
A/D
LTC1748
5V
AMPLITUDE (dB)
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
66002 TA01a
–
V
MID
V
OCM
+
–
4
49.9Ω
18pF
+
A
IN
V
+
D
OUT
V
CM
V
–
1µF
49.9Ω
5
+
6
–
GAIN = 402Ω/R
IN
0
U
INPUT 5.9MHz
2V
P-P
f
SAMPLE
= 80MHz
10
20
FREQUENCY (MHz)
66002 TA01b
U
U
30
40
66002f
1
LT6600-20
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
IN
–
1
V
OCM
2
V
+
3
OUT
+
4
8
7
6
5
IN
+
V
MID
V
–
OUT
–
Total Supply Voltage ................................................ 11V
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
ORDER PART
NUMBER
LT6600CS8-20
LT6600IS8-20
S8 PART MARKING
660020
600I20
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications that 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)
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)
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz, V
S
= 3V
V
IN
= 2V
P-P
, f
IN
= DC to 260kHz, V
S
= 5V
V
IN
= 2V
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
2nd Harmonic
3rd Harmonic
20MHz, 2V
P-P
, R
L
= 800Ω
2nd Harmonic
3rd Harmonic
Measured Between Pins 4 and 5
V
S
= 5V
V
S
= 3V
Average of Pin 1 and Pin 8
MIN
– 0.4
– 0.1
– 0.2
– 0.1
– 0.8
TYP
0.1
0
0.1
0.5
0
– 33
– 50
0
0
0.1
0.4
–0.4
– 33
– 50
– 0.1
12.1
12.0
11.9
780
118
83
88
63
64
4.75
4.50
– 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
12.6
12.5
12.4
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
ppm/C
µV
RMS
dBc
dBc
dBc
dBc
V
P-P DIFF
V
P-P DIFF
µA
ELECTRICAL CHARACTERISTICS
q
q
q
q
q
q
q
q
q
q
q
q
Filter Gain, V
S
= 5V
– 0.5
– 0.1
– 0.2
– 0.3
– 1.3
Filter Gain, V
S
=
±5V
Filter Gain, R
IN
= 100Ω
– 0.6
11.6
11.5
11.4
Filter Gain Temperature Coefficient (Note 2)
Noise
Distortion (Note 4)
Differential Output Swing
Input Bias Current
q
q
q
3.80
3.75
– 95
66002f
2
U
W
U
U
W W
W
LT6600-20
The
q
denotes specifications that 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
Input Referred Differential Offset
CONDITIONS
R
IN
= 402Ω
MIN
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
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
R
IN
= 100Ω
Differential Offset Drift
Input Common Mode Voltage (Note 3)
TYP
5
10
10
5
5
5
10
MAX
25
30
35
15
17
20
1.5
3.0
1.0
1.5
3.0
2.0
40
40
35
2.55
7.65
Differential Input = 500mV
P-P
,
R
IN
= 100Ω
Differential Input = 2V
P-P
,
Pin 7 at Mid-Supply
Common Mode Voltage at Pin 2
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
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
UNITS
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
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
66002f
3
LT6600-20
TYPICAL PERFOR A CE CHARACTERISTICS
Amplitude Response
10
0
–10
–20
GAIN (dB)
–40
–50
–60
–70
–80
V
S
= 5V
GAIN = 1
T
A
= 25°C
1
10
FREQUENCY (MHz)
100
66002 G01
GAIN (dB)
GAIN (dB)
–30
–90
0.1
Passband Gain and Group Delay
14
12
10
8
GAIN
V
S
= 5V
GAIN = 4
T
A
= 25°C
50
45
OUTPUT IMPEDANCE (Ω)
GAIN (dB)
6
4
2
0
–2
–4
–6
0.5
30
25
20
15
10
5
CMRR (dB)
GROUP
DELAY
6.5
18.5
24.5
12.5
FREQUENCY (MHz)
Power Supply Rejection Ratio
100
90
80
70
V
+
TO DIFFOUT
V
S
= 3V
T
A
= 25°C
DISTORTION (dB)
–60
–70
–80
–90
DISTORTION (dB)
PSRR (dB)
60
50
40
30
20
10
0
0.001
0.01
0.1
1
FREQUENCY (MHz)
4
U W
66002 G04
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
2
0
–2
–4
Passband Gain and Group Delay
GAIN
V
S
= 5V
GAIN = 1
T
A
= 25°C
50
45
40
35
GROUP
DELAY
30
25
20
15
10
5
6.5
18.5
24.5
12.5
FREQUENCY (MHz)
0
30.5
66002 G03
GROUP DELAY (ns)
PHASE (DEG)
–85
–130
–175
–6
–8
–10
–12
–14
–16
–18
0.5
–220
–265
–310
–355
30.5
66002 G02
Output Impedance
100
V
S
= 5V
GAIN = 1
T
A
= 25°C
80
75
70
65
60
55
50
45
40
35
Common Mode Rejection Ratio
INPUT = 1V
P-P
V
S
= 5V
GAIN = 1
T
A
= 25°C
40
35
GROUP DELAY (ns)
10
1
0
30.5
0.1
0.1
30
1
10
FREQUENCY (MHz)
100
66002 G05
0.1
1
10
FREQUENCY (MHz)
100
66002 G06
Distortion vs Frequency
–40
–50
DIFFERENTIAL INPUT,
2ND HARMONIC
DIFFERENTIAL INPUT,
3RD HARMONIC
SINGLE-ENDED INPUT,
2ND HARMONIC
SINGLE-ENDED INPUT,
3RD HARMONIC
–40
–50
–60
–70
–80
–90
–100
Distortion vs Signal Level,
V
S
= 3V
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
–100
10
100
66002 G07
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
0
1
2
3
INPUT LEVEL (V
P-P
)
4
5
66002 G09
66002f
LT6600-20
TYPICAL PERFOR A CE CHARACTERISTICS
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)
–60
–70
–80
–90
DISTORTION COMPONENT (dB)
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
DISTORTION COMPONENT (dB)
Total Supply Current
vs Total Supply Voltage
60
T
A
= 85°C
T
A
= 25°C
T
A
= –40°C
TOTAL SUPPLY CURRENT (mA)
50
40
30
20
10
0
0
1
2 3 4 5 6 7 8
TOTAL SUPPLY VOLTAGE (V)
U W
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
–40
–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
–50
–100
–3
–2
–1
0
1
2
3
INPUT COMMON MODE VOTLAGE RELATIVE TO PIN 7 (V)
66002 G11
–100
500mV
P-P
1MHz INPUT, GAIN = 4,
R
L
= 800Ω AT EACH OUTPUT
–3
–2
–1
0
1
2
3
INPUT COMMON MODE VOTLAGE RELATIVE TO PIN 7 (V)
66002 G12
Distortion
vs Output Common Mode
–40
–50
–60
–70
–80
–90
–100
–110
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
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
66002 G13
Transient Response, Gain = 1
V
OUT+
50mV/DIV
DIFFERENTIAL
INPUT
200mV/DIV
100ns/DIV
66002 G15
9
10
66002 G14
66002f
5
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