Datasheet

LMV721-N, LMV722-N

SNOS414I –AUGUST 1999–REVISED AUGUST 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 29). As in the two-op-amp circuit, this instrumentation amplifier requires precise resistor

matching for good CMRR. R

should equal to R

and R

should equal R

Figure 29. Two-op-amp Instrumentation Amplifier

(3)

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 R

and R

is implemented to bias the amplifier so the

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

is placed

between the inverting input and resistor R

to block the DC signal going into the AC signal source, V

. The

values of R

and C

affect the cutoff frequency, fc = ½π R

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 30. Single-Supply Inverting Amplifier

(4)

Active Filter

Simple Low-Pass Active Filter

The simple low-pass filter is shown in Figure 31. Its low-pass frequency gain (ω → o) is defined by −R

. This

allows low-frequency gains other than unity to be obtained. The filter has a −20dB/decade roll-off after its corner

frequency fc. R

should be chosen equal to the parallel combination of R

and R

to minimize error due to bias

current. The frequency response of the filter is shown in Figure 32.

Product Folder Links: LMV721-N LMV722-N