FM DETECTION CIRCUIT

摘要

PURPOSE:To attain a high degree of integration for an IC by using digital circuits only to constitute an FM detection circuit. CONSTITUTION:A zero cross detector detects a zero cross by checking the highest bit of the data Xn given from an input terminal and the preceding data Xn-1 which is delayed by a sampling cycle through the 1st delay device. At the same time, the new data Y is obtained by the 1st subtractor. Then the data Y is divided by a ratio between the interpolation frequency and the sampling frequency through a divider to obtain the data Y'. The data Y' are added successively by an adder and the 2nd delay device to obtain the data Y''. The data Y' is subtracted from the data Xn-1 by the 2nd subtractor to obtain the data f(t). This data f(t) is obtained by giving the linear interpolation between data Xn and Xn-1. Thus it is possible to obtain an accurate zero cross time point by checking the polarity of the data f(t). A monostable oscillator delivers pulses for a fixed period of time at said zero cross time point. Then a demodulation signal is obtained via an LPF.