Frequency modulation detector using digital signal vector processing

摘要

A frequency modulated signal is converted into a pair of baseband signals by mixing the signal with a pair of phase-quadrature reference signals of substantially carrier center frequency. The double reference frequency component of each of the baseband signals is filtered to obtain I and Q signals. The I and Q signals constitute in rectangular coordinates the components of a vector represented in polar coordinates by R and theta where R is the maximum amplitude of the I and Q signals and theta is the instantaneous angle represented by the arctangent of the I signal divided by the Q signal. The I and Q signals are inverted to provide respective -I and -Q signals. The I, -I, Q, -Q signals are sampled to provide a sequence of sets of signal samples. For each set of signal samples the angle theta is obtained. A sequence of changes in the values of the angle theta over successive sampling periods is obtained and represents the deviation in frequency of the FM carrier corresponding to changes in amplitude of the modulating signal.