Patent ID: 7443930

Claim:
A demodulator for demodulating a complex digital input signal, comprising: filters operable to filter the complex digital input signal to produce a filtered complex digital input signal; a complex digital phase locked loop including: a phase detector connected to receive the filtered complex digital input signal and a complex digital feedback signal, wherein the phase detector is operable to produce a phase error indicative of a difference in phase between the filtered complex digital input signal and the complex digital feedback signal, a controller connected to receive the phase error, wherein the controller is operable to multiply the phase error by a gain factor selected to stabilize and optimize the complex digital phase locked loop and to produce an output signal for use in extracting a frequency deviation present in the complex digital input signal, wherein the gain factor is selected by determining a stability region in the complex plane associated with the phase locked loop as a function of integration gain coefficient values and proportionality gain coefficient values; and a numerically controlled oscillator connected to receive the output signal, wherein the numerically controlled oscillator is operable to track the phase of the complex digital input signal based on the output signal and produce the complex digital feedback signal; and a data and timing recovery circuit operable to determine optimal sampling points of the output signal and to produce a demodulated digital signal.