KFM frequency tracking system using a digital correlator

Apparatus for providing a two point phase/frequency modulation system, the apparatus comprising:

• a first network configured to introduce an offset to center a signal applied to a VCO;
• a second network configured to set a gain of the VCO;
• and
• a phase tracking network configured to dynamically adjust the offset and the gain;
• wherein the phase tracking network includes a correlator network operative to track an error signal applied to the VCO and
• wherein the correlator network includes:
• a subtracting integrator;
• a window comparator coupled to an output of the subtracting integrator;
• and
• a correlator coupled to an output of the window comparator.

Apparatus for tracking in a two point phase/frequency modulation system to adjust an offset and scale of a signal applied to a VCO, the apparatus comprising:

• a subtracting integrator configured to capture a dynamic correction signal;
• a window comparator configured to determine a polarity of an output signal of the integrator;
• a correlator network configured to project the dynamic correction signal onto a reference modulation signal;
• and
• logic configured to generate, based on the output signal of the correlator, a control signal (Voff) to adjust the offset of a signal applied to the VCO and a control signal (Valpha) to scale the signal applied to the VCO.

Apparatus for tracking the operation of a two point phase/frequency modulation system to adjust the offset and/or the scaling applied to the signal driving the VCO, the apparatus comprising:

• a subtracting integrator configured to capture a dynamic correction signal;
• an A/D converter for measuring an output of the integrator;
• a correlator configured to project the dynamic correction signal onto a reference modulation signal and produce a correlation signal;
• logic configured to generate, based on the output signal of the correlator, a control signal (Voff) to adjust the offset of a signal applied to the VCO and a control signal (Valpha) to scale the signal applied to the VCO.

A phase/frequency modulation system, comprising:

• a phase-locked loop (PLL) having a VCO including a first port and a second port wherein during operation of the PLL an error signal is received by the first port;
• a correlator network configured to produce an output signal based upon the error signal and a function of an applied FM modulation signal;
• and
• a phase tracking loop which generates, in response to the output signal, a VCO control signal applied to the second port.

A method for providing two point phase/frequency modulation, comprising:

• generating an offset signal;
• providing the offset signal to center a modulation signal applied to a VCO element of a phase-locked loop;
• generating a gain signal;
• providing the gain signal to set a gain of the VCO;
• and
• dynamically tracking, during operation of the phase-locked loop, the offset and the gain of the VCO so as to generate one or more additional correction signals to be applied to the VCO.

A method for tracking the relationship between a direct modulation FM signal applied to a phase-locked loop (PLL) and a PLL feedback signal, comprising:

• generating, using cross-correlation between the FM signal and feedback signal, a correlation signal that:
• follows the FM signal when the FM signal is scaled below a first predefined scaling threshold;
• and
• moves opposite to the FM signal when the FM signal is scaled above a second predefined threshold;
• and
• providing said correlation signal to the PLL so as to adjust the output of a VCO element of the PLL.