DC OFFSET COMPENSATION FOR ZERO IF QUADRATURE DEMODULATOR

摘要

The present invention provides a kind of introducing frequency deviations of the AMPS cellular mobile telephone systems of zero IF FM quadrature demodulators of DC offset compensation circuit (800) to modulate modulated signal of the intrinsic DC component from supervisory audio tone and Manchester code to remove. Local oscillator (608) slightly has difference with frequency, such as from 5 kHz of frequency, mixed signal intermediate-freuqncy signal is transformed to 0 in this way. A direct-flow shifted signal is generated using control loop, to eliminate DC component local oscillator (608) caused by fixed leak. After a period of time,Control loop can be freezed, be removed with the local oscillator (608) of above-mentioned frequency deviation.