LMV321-N, LMV321-N-Q1, LMV358-N, LMV358-N-Q1
LMV324-N, LMV324-N-Q1
SNOS012I –AUGUST 2000–REVISED FEBRUARY 2013
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Figure 57. Two-Op-Amp Instrumentation Amplifier
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-mode 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 = 1/2πR1C1.
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 58. Single-Supply Inverting Amplifier
ACTIVE FILTER
Simple Low-Pass Active Filter
The simple low-pass filter is shown in Figure 59. Its low-frequency gain (ω → 0) 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 bias
current. The frequency response of the filter is shown in Figure 60.
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