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Amplifiers
A.3.19 Noninverting AC Amplifier
V CC and the resistors (R) set a dc level of V CC /2 at the inverting input. R G is connected
to ground through a capacitor, thus the circuit functions as a buffer for dc. This causes the
dc output voltage to be V CC /2, so the quiescent output voltage is the middle of the supply
voltage, and it is ready to swing to either rail as the input signal commands.
The ac gain is given in Equation A–27. R G and C create a coupling network for the ac signal.
Good coupling networks should be a constant low impedance at the signal frequencies,
so Equation A–28 should be satisfied to get good low frequency performance. The
lowest frequency component of the input signal, f MIN , is determined by completing a Fourier
series on the input signal. Then, setting f MIN = 100f in Equation A–28 ensures that the
3-dB breakpoint introduced by R G and C is two decades lower than f MAX . The breakpoint
for R G and C 1 is set in a similar manner.
R
V OUT
V F
R G
IN
V CC
R G
2 R F R G
R G
f
1
200R G
C
A–27
A–28
V IN
C
C
R G
+V CC
R
R F
+V CC
_
+
R
V OUT
Output Amplitude — dB
10
6
2
–2
–6
–10
–14
–18
–22
–26
V OUT
Phase
90
80
70
60
50
40
30
20
10
–30 –10
10 100 1 k 10 k 100 k
f – Frequency – Hz
0
Phase — Degrees
V IN = 1 Vp-p
C = 0.01 F
V CC = 5 V R G = R F = R = 10 k
Op Amp = TLV247x
Figure A–23. Noninverting AC Amplifier
Single-Supply Circuit Collection
A-23