LT6600-20_15 Datasheet, PDF (1/12 Pages) Linear Technology – Very Low Noise, Differential Amplifi er and 20MHz Lowpass Filter

LT6600-20
Very Low Noise, Differential
Amplifier and 20MHz Lowpass Filter
FEATURES
n _{Programmable Differential Gain via Two External}
Resistors
n _{Adjustable Output Common Mode Voltage}
n _{Operates and Specified with 3V, 5V, ±5V Supplies}
n _{0.5dB Ripple 4th Order Lowpass Filter with 20MHz}
Cutoff
n _{76dB S/N with 3V Supply and 2VP-P Output}
n _{Low Distortion, 2VP-P, 800Ω Load}
2.5MHz: 83dBc 2nd, 88dBc 3rd
20MHz: 63dBc 2nd, 64dBc 3rd
n _{Fully Differential Inputs and Outputs}
n _{SO-8 Package}
n _{Compatible with Popular Differential Amplifier}
Pinouts
APPLICATIONS
n _{High Speed ADC Antialiasing and DAC Smoothing in}
Networking or Cellular Base Station Applications
n _{High Speed Test and Measurement Equipment}
n _{Medical Imaging}
n _{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.
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.
TYPICAL APPLICATION
LT6600-20
5V
0.1μF
R_IN
402Ω
1
7
3
–
V_MID
+
4
0.01μF
V_IN
2
8
V_OCM
+
–
5
R_IN
6
402Ω
49.9Ω
49.9Ω
GAIN = 402Ω/R_IN
A/D
LTC1748
5V
+
18pF
A_IN
–
V_CM
V⁺
D_OUT
V^–
1μF
66002 TA01a
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
An 8192 Point FFT Spectrum
INPUT 5.9MHz
2V_P-P
f_SAMPLE = 80MHz
10
20
30
40
FREQUENCY (MHz)
66002 TA01b
66002fb
1