Datasheet

GAIN 0-3
100:
5
LMH6881
V
CC
0.01 PF
0.01 PF
49.9:
49.9:
SD
OCM
1.25V
CAT5
Rx
100:
:
:
GAIN 0-3
100:
ADS5400
5
RF
LO
LMH6881
+5V
0.01 PF
0.01 PF
49.9:
49.9:
SD
100:
FILTER
100:
FILTER
OCM 1.25V
2.5V
LMH6881
SNOSC72E –JUNE 2012–REVISED MARCH 2013 www.ti.com
APPLICATION INFORMATION
INTRODUCTION
The LMH6881 has been designed to replace traditional, fixed-gain amplifiers, as well as variable-gain amplifiers,
with an easy-to-use device which can be flexibly configured to many different gain settings while maintaining
excellent performance over the entire gain range. Many systems can benefit from this programmable-gain, DC-
capable, differential amplifier. Last-minute design changes can be implemented immediately, and external
resistors are not required to set the gain.
Gain control is enabled with a parallel or a serial-control interface, and as a result, the amplifier can also serve as
a digitally controlled variable-gain amplifier (DVGA) for automatic gain-control applications. Figure 36 and
Figure 37 show typical implementations of the amplifier.
Figure 36. LMH6881 Typical Application
Figure 37. LMH6881 Used as Twisted Pair Cable Driver
This application section will cover the use and function of the amplifier, common applications, detailed
instructions on digital control and power supply as well as thermal and board layout recommendations.
BASIC CIRCUIT DESCRIPTION
The LMH6881 has three functional stages, a low-noise amplifier, followed by a digital attenuator, and a low-
distortion, low-impedance output amplifier. The amplifier has four signal-input pins, to accommodate both
differential signals and single-ended signals. The amplifier has an OCM pin used to set the output common mode
voltage. There is a gain of 2 on this pin so that 1.25 V applied on that pin will place the output common mode at
2.5 V.
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