2-46
Figure 2-32.—Lin-Log amplifier versus normal IF amplifier.
A typical circuit for obtaining a lin-log response is shown in figure 2-33. If detectors 2 and 3 were
not present, the output voltage would be limited by the saturation point of the final IF stage, as it is in a
normal IF section. However, when the final stage of the lin-log is saturated, larger signals cause an
increase in the output of the next to last stage. This increase is detected by detector 2 and summed with
the output of detector 1. This sum produces an increase in the output even though the final stage is
saturated. Detector 3 causes the output to continue to increase after the second stage saturates. The overall
gain becomes less and less as each stage saturates, but some degree of amplification is still available. The
proper choice of IF stage gains and saturation points produces an approximately logarithmic response
curve.
Figure 2-33.—Lin-Log receiver block diagram.
Figure 2-34, shows the response curves of the three IF stages in the lin-log amplifier shown in figure
2-33. The responses of the individual stages produce a segmented overall response curve for the receiver.
