Signal generator with direct digital synthesis and tracking filter

An apparatus comprising:

• an oscillator signal generator configured to generate an oscillator signal, the oscillator signal generator comprising:
• a digital signal generator configured to generate a digital signal;
• a digital to analog converter (DAC) configured to receive and convert the digital signal to an analog signal;
• a filter configured to receive and filter the analog signal and generate the oscillator signal;
• a comparator configured to receive the oscillator signal and generate a comparator output signal indicating zero crossings of the oscillator signal;
• a digital control unit (DCU) configured to receive the comparator output signal and the digital signal and to generate a control signal to tune the filter to track a center frequency of the digital signal,
• the control signal being based at least in part on adjacent samples of the digital signal before and after zero crossings of the oscillator signal.

A method for generating an oscillator signal in an oscillator signal generator, the oscillator signal generator having a digital signal generator, a digital to analog converter (DAC), a filter, a comparator and a digital control unit, the method comprising:

• generating by the digital signal generator, a digital signal;
• converting by the DAC, the digital signal to an analog signal;
• filtering by the filter, the analog signal to generate the oscillator signal;
• generating by the comparator, a signal indicating zero crossings of the oscillator signal;
• summing in the digital control unit, two adjacent samples of the digital signal before and after a zero crossing of the oscillator signal;
• weighting in the digital control unit, the sum value with a coefficient;
• generating in the digital control unit, a control signal based on the weighted sum value;
• and
• tuning the filter by the control signal to track a center frequency of the oscillator signal.