Complex digital phase locked loop for use in a demodulator and method of optimal coefficient selection
AssigneeBroadcom Corporation
InventorHenrik T. Jensen
Life of this patent
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Abstract
A complex digital phase locked loop for use in a digital demodulator includes a phase detector for producing a phase error indicative of a difference in phase between a complex digital input signal and a complex digital feedback signal. The phase error is input to a controller, which multiplies the phase error by a gain factor selected to stabilize and optimize the phase locked loop and produces an output signal for use in extracting a frequency deviation present in the complex digital input signal. The output signal is also input to a numerically controlled oscillator that tracks the phase of the complex digital input signal based on the output signal and produces the complex digital feedback signal.
Claims15
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.
A method for selecting an optimal integration gain coefficient value and an optimal proportionality gain coefficient value for use in a complex digital phase locked loop of a demodulator operable to demodulate a complex digital input signal, comprising the steps of:
- 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;
- dividing the stability region into discrete points, each representing a specific one of the integration gain coefficient values and a corresponding specific one of the proportionality gain coefficient values;
- and
- sweeping the demodulator over each of the discrete points under strenuous operating conditions to determine the optimal integration gain coefficient value and the optimal proportionality gain coefficient value.
Dependencies are inferred from the claim text.