4.3 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

implemented to bias the amplifier so the input signal is within

the input common-common voltage range of the amplifier.

The capacitor C

resistor R

source, V

π R

As a result, the output signal is centered around mid-supply

(if the voltage divider provides V

put). The output can swing to both rails, maximizing the

signal-to-noise ratio in a low voltage system.

4.4 Active Filter

4.4.1 Simple Low-Pass Active Filter

The simple low-pass filter is shown in

Figure 9. Its low-pass

frequency gain (

ω → o) is defined by −R

low-frequency gains other than unity to be obtained. The fil-

ter has a −20dB/decade roll-off after its corner frequency fc.

R

and R

response of the filter is shown in

Figure 10.

Note that the single-op-amp active filters are used in to the

applications that require low quality factor, Q(

≤ 10), low fre-

quency (

≤ 5KHz), and low gain (≤ 10), or a small value for the

product of gain times Q(

≤ 100). The op amp should have an

open loop voltage gain at the highest frequency of interest at

least 50 times larger than the gain of the filter at this fre-

quency. In addition, the selected op amp should have a slew

rate that meets the following requirement:

Slew Rate

≥ 0.5x(ω

Where

ω

the output peak-to-peak voltage.

DS100922-22

FIGURE 7. Two-op-amp Instrumentation Amplifier

DS100922-23

FIGURE 8. Single-Supply Inverting Amplifier

DS100922-24

FIGURE 9. Simple Low-Pass Active Filter

DS100922-25

FIGURE 10. Frequency Response of Simple Low-pass

Active Filter in

Figure 9

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