Demodulator circuit and method of tuning

摘要

A demodulator circuit (10) includes an oscillator (12) and an injection circuit (14). An Automatic Frequency Control (AFC) signal adjusts the tail current of a current source (28) provided in the oscillator (12) and the tail current of a current source (44) provided in the injection circuit (14). A phase detector (16) compares the phase of the signal generated by the oscillator (12) with the phase of the injected input signal. The phase detector (16) generates an output signal V0 having a value of zero when the input signal is in quadrature with the signal generated by the oscillator (12), but generates a non-zero signal that is used to adjust the AFC signal when the input signal and the signal generated by the oscillator (12) are not in quadrature.