DC offset compensation for zero-IF demodulator right angle

摘要

(57) [summary] The present invention provides a (800) DC offset compensation circuit for the FM demodulator right angle of zero IR in the AMPS cellular mobile telephone system. Frequency offset is introduced in order to remove the DC component-specific modulation and Manchester coding and supervisory audio tone from the modulated signal. Local oscillator (608), slightly from the frequency to mix down to zero intermediate frequency signal, for example, operating at different frequencies 5kHz. DC offset is generated by the control loop in order to eliminate the DC component of constant caused by leakage from the local oscillator (608). After a given time, the control loop is not working, the frequency offset of the local oscillator (608) is removed.