
188 Analog Circuits Cookbook
-Vcc
Figure
6.15 Bipolar (prebiased) photoconductive isolation amplifier
Figure 6.15 shows a bipolar photoconductive isolation amplifier, using
rudimentary constant voltage sources for prebias. Note that
IP<i
flows
through a 60 KQ resistor against 30 KQ for IP\, to restore the gain to
unity, allowing for the 2:1 attenuation pad at the input; consequently, twice
the prebias voltage is needed in the output circuit. This circuit was substi-
tuted for the A\ and A^ circuit in Figure 6.11 and the 50 Hz distortion test
repeated. (Because the circuit in Figure 6.15 circuit is inverting, amplifier
A<$
in Figure 6.11 was