Page 116 - Op Amps Design, Applications, and Troubleshooting
P. 116
AC-Coupled Amplifier 99
Our next step is to compute the effects of C 0 and R L. These two components
form an RC voltage divider. You may apply your favorite circuit analysis
method to determine the percentage of voltage that appears across JR L. This per-
centage is the effective "gain" of the RC-coupling circuit. For our purposes, we
will use the following method, which is based on the resistive voltage divider
formula:
where Z is the net impedance of C 0 and R L.
First we compute the reactance of C 0 at the frequency of interest (800 hertz in
this case):
1
Next we compute the net impedance of R L and C 0:
Finally, substituting this value into Equation (2.38), we compute our gain as
That is to say, about 97% of the signal amplitude that appears at the output termi-
nal of the op amp will be developed across R L. The RC-coupling circuit appears to
be working well at 800 hertz, since very little voltage is being lost across C 0.
The overall voltage gain for the circuit is found by multiplying these two
gains as computed.
