In a method for designing an envelope detecting circuit for a video signal
processing integrated circuit (IC), the number of peripheral components
of the video signal processing IC is minimized by incorporating, into the
video signal processing IC, a circuit device for detecting the envelope
of an FM video signal and for controlling the envelope level. According
to the IC designing method, the number of components can be reduced by
designing all circuit elements constituting a circuit which detects the
envelope of the FM video signal and which controls envelope level so that
they are incorporated into the video signal processing IC at the time of
designing the video signal processing IC. As a result, cost is reduced
and, since mode control signal lines are reduced, the corresponding
terminals of the microprocessor can be used for another purpose, thereby
increasing the operating efficiency of the microprocessor.