LPV321 datasheet(13/28 Pages) TI1

13 / 28 page

LPV321, LPV324-N, LPV358-N

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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 R1, R2, R3, and R4. 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 M

Ω. The gain of this

instrumentation amplifier is set by the ratio of R2/R1. R3 should equal R1 and R4 equal R2. Matching of R3 to R1

and R4 to R2 affects the CMRR. For good CMRR over temperature, low drift resistors should be used. Making R4

Slightly smaller than R 2 and adding a trim pot equal to twice the difference between R 2 and R4 will allow the

CMRR to be adjusted for optimum.

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