Datasheet

LMV721-N, LMV722-N
www.ti.com SNOS414I –AUGUST 1999–REVISED AUGUST 2013
TYPICAL SINGLE-SUPPLY APPLICATION CIRCUITS
Difference Amplifier
The difference amplifier allows the subtraction of two voltages or, as a special case, the cancellation of a signal
common to two inputs. It is useful as a computational amplifier, in making a differential to single-ended
conversion or in rejecting a common mode signal.
Figure 27. Difference Application
(1)
(2)
Instrumentation Circuits
The input impendance of the previous difference amplifier is set by the resistor R
1
, R
2
, R
3
and R
4
. To eliminate
the problems of low input impendance, one way is to use a voltage follower ahead of each input as shown in the
following two instrumentation amplifiers.
Three-op-amp Instrumentation Amplifier
The LMV721-N/722 can be used to build a three-op-amp instrumentation amplifier as shown in Figure 28
Figure 28. Three-op-amp Instrumentation Amplifier
The first stage of this instrumentation amplifier is a differential-input, differential-output amplifier, with two voltage
followers. These two voltage followers assure that the input impedance is over 100MΩ. The gain of this
instrumentation amplifier is set by the ratio of R
2
/R
1
. R
3
should equal R
1
and R
4
equal R
2
. Matching of R
3
to R
1
and R
4
to R
2
affects the CMRR. For good CMRR over temperature, low drift resistors should be used. Making R
4
slightly smaller than R
2
and adding a trim pot equal to twice the difference between R
2
and R
4
will allow the
CMRR to be adjusted for optimum.
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