Digital phase lock detector

A digital phase lock detector for use in a Doppler radar system for determining the speed of a target vehicle, said radar system including detector means for generating a difference Doppler signal having a frequency which is proportional to the velocity of the target vehicle, said digital phase lock detector comprising:

• bandpass filter means responsive to said difference signal for generating a periodic signal having a frequency which is varied in accordance with the velocity of the target vehicle, said bandpass filter means having a variable center frequency;
• comparator means responsive to said periodic signal for generating a rectangular pulse signal which is a digital representation of said periodic signal;
• controller means operated under a stored program and being responsive to said pulse signal for determining the period of said pulse signal by integrating a number of consecutive cycles to produce a synthesized Doppler frequency signal having a frequency which is proportional to the velocity of the target vehicle;
• dividing means interconnected between said comparator means and said controller means for dividing down the frequency of said pulse signal;
• multiplier means interconnected between said controller means and said bandpass filter means for multiplying the frequency of said synthesized Doppler signal;
• said multiplier means being formed of a phased-locked loop and counter means for generating said synthesized Doppler signal having a frequency which is a multiple of the center frequency of said bandpass filter means;
• and
• said bandpass filter means being responsive to said synthesized Doppler frequency signal for varying the center frequency thereof to track the difference Doppler signal.