Patent ID: 7245872

Claim:
A switching circuit for a broadcasting satellite converter wherein two local oscillators having different oscillation frequencies are switched in accordance with whether a band switching pulse signal having a given frequency is superimposed on a power supply voltage transmitted from a broadcasting satellite tuner, said switching circuit comprising: a monostable multivibrator circuit to which said power supply voltage is input from said broadcasting satellite tuner, and in which input pulses are converted into pulses having a given time width; a first integrating circuit which integrates an output of said monostable multivibrator circuit to output a signal having a level corresponding to a duty factor of the output of said monostable multivibrator circuit; a determining circuit having a delay circuit to which the output of said monostable multivibrator circuit is input, and determining whether an output of said first integrating circuit falls within a given range at a timing of an output of said delay circuit; and a driver circuit which drives a local oscillator having an oscillation frequency corresponding to an output of said determining circuit.