Datasheet

LPV321, LPV324-N, LPV358-N
www.ti.com SNOS413D –AUGUST 2000–REVISED MARCH 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 44. Difference Amplifier
(1)
Instrumentation Circuits
The input impedance 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 impedance, 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 quad LPV324 can be used to build a three-op-amp instrumentation amplifier as shown in Figure 45
Figure 45. 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 100 MΩ. 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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