High frequency receiving circuit for mobile communication apparatus

Abstract

A receiving wave containing a desired signal and received through an antenna is inputted to an interstage band-pass filter 4 after the component outside a receiving band of the receiving wave has been attenuated by a receiving band-pass filter 2a. A phase locked loop circuit 9 outputs a frequency control voltage corresponding to a selected channel to a voltage control oscillator 8 and also outputs this frequency control voltage to an interstage band-pass filter 4 as a band control voltage thereof. The voltage control oscillator 8 generates a local carrier wave in response to the frequency control voltage. The interstage variable band-pass filter 4 has a passing band width which is a little wider than channel band width and varies its passing band in response to the band control voltage so as to include the selected channel, thereby attenuating the component outside the passing band of the receiving wave inputted from the low noise amplifier 3 and then inputs the receiving wave to a mixer 5. Accordingly, if a frequency which causes a single-signal interference is located in the receiving band apart from the selected channel frequency by a half of the intermediate frequency, the interference wave of this frequency can be attenuated.