LPV321 datasheet(14/28 Pages) TI1

14 / 28 page

LPV321, LPV324-N, LPV358-N

SNOS413D – AUGUST 2000 – REVISED MARCH 2013

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Two-op-amp Instrumentation Amplifier

A two-op-amp instrumentation amplifier can also be used to make a high-input-impedance DC differential

amplifier (Figure 46). As in the three-op-amp circuit, this instrumentation amplifier requires precise resistor

matching for good CMRR. R4 should equal to R1 and R3 should equal R2.

Figure 46. Two-op-amp Instrumentation Amplifier

(2)

Single-Supply Inverting Amplifier

There may be cases where the input signal going into the amplifier is negative. Because the amplifier is

operating in single supply voltage, a voltage divider using R3 and R4 is implemented to bias the amplifier so the

input signal is within the input common-common voltage range of the amplifier. The capacitor C1 is placed

between the inverting input and resistor R1 to block the DC signal going into the AC signal source, VIN. The

values of R1 and C1 affect the cutoff frequency,

fc = 1/2

π R 1C1

(3)

As a result, the output signal is centered around mid-supply (if the voltage divider provides V+/2 at the non-

inverting input). The output can swing to both rails, maximizing the signal-to-noise ratio in a low voltage system.

Figure 47. Single-Supply Inverting Amplifier

(4)

Active Filter

Simple Low-Pass Active Filter

The simple low-pass filter is shown in Figure 48. Its low-frequency gain(

ω → o) is defined by −R3/R1. This allows

low-frequency gains other than unity to be obtained. The filter has a

−20 dB/decade roll-off after its corner

frequency fc. R2 should be chosen equal to the parallel combination of R1 and R3 to minimize errors due to bais

current. The frequency response of the filter is shown in Figure 49

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