Wideband digital frequency discriminator and phase and frequency detector

A digital discriminator for demodulating an FM signal comprising:

• (a) means for producing a reference signal having a period which is related to the period of the center frequency of the FM signal;
• (b) counting means operative at the rate of the FM signal for generating at the output thereof a cyclical signal comprising a repeated series of nonambiguous states;
• (c) means for sampling the state of the cyclical signal generated at the output of said counting means at a rate determined by said reference signal and for storing at least two consecutive sampled states of said cyclical signal;
• and
• (d) detection means operating at a rate determined by said reference signal and connected to receive said stored sampled states for detecting a state difference between the sampled states of said cyclical signal, said detection means generating an output signal when a state difference is detected.

A digital discriminator for demodulating an FM signal comprising:

• (a) a counter operating at the frequency of the FM signal for generating a cyclical output signal comprising a predetermined number of sequential nonambiguous states;
• (b) means for generating a reference signal;
• (c) first and second latches for storing states of said cyclical signal, said first latch actuated synchronously with said reference signal for sampling and storing the present state of said cyclical signal, said second latch actuated synchronously with said reference signal for sampling and storing the state signal stored in said first latch to obtain the immediately preceding sampled state of said cyclical signal;
• and
• (d) detection means actuated synchronously with said reference signal and connected to receive the state signal stored in said first latch and said second latch, said detection means generating an output signal when the two state signals received by said detection means are different.

A digital discriminator for demodulating an FM signal comprising:

• (a) a counter operating at the frequency of the FM signal for generating a cyclical output signal comprising a predetermined number of sequential nonambiguous states;
• (b) means for generating a reference signal;
• (c) first and second latches for storing states of said cyclical signal, said first latch actuated synchronously with said reference signal for sampling and storing the present state of said cyclical signal, said second latch actuated synchronously with said reference signal for sampling and storing the state signal stored in said first latch to obtain the immediately preceding sampled state of said cyclical signal;
• (d) means for receiving the state signal stored in said first latch and generating a state signal corresponding to a state of said sequential nonambiguous states advanced by a predetermined number of states from the state received from said first latch;
• and
• (e) detection means actuated synchronously with said reference signal and connected to receive the state signal stored in said second latch and the advanced state signal generated by said means for receiving, said detection means generating an output signal when the two state signals received by said detection means are different, said output signal indicating whether said state change is increasing or decreasing.

A wideband digital discriminator for demodulating an FM signal comprising:

• (a) a ring counter for generating in synchronism with the FM signal a cyclical signal having recurring X number of sequential nonambiguous states;
• (b) means for generating a reference signal where K is the ratio of the center frequency of the FM signal to the frequency of the reference signal;
• (c) means for sampling the state of said cyclical signal in synchronism with said reference signal and for storing the present and immediately preceding sampled state of said cyclical signal;
• (d) means for generating an advanced state signal having a state of said nonambiguous states advanced N states ahead of said present sampled cyclical state where N+K=X;
• (e) means for detecting a state difference between said advanced state and said preceding state;
• and
• (f) means for generating an output signal when a state difference is detected.

Apparatus for measuring the phase and frequency difference between an FM signal and a reference signal comprising:

• (a) counting means operating at the frequency of the FM signal for generating at the output thereof a cyclical signal having a recurring series of nonambiguous states;
• (b) means for generating a reference signal having a known frequency;
• (c) means for sampling the state of the cyclical signal generated at the output of said counting means at a rate determined by said reference signal and for storing the present sampled state and immediately preceding sampled state;
• (d) detection means operating at a rate determined by said reference signal and connected to receive said stored sampled states for detecting a state change between said stored sampled states and the direction of said change, said detection means generating an output signal which indicates the detection of a state change and the direction thereof;
• (e) means for detecting the phase difference between the FM signal and the reference signal and generating a phase signal proportional to said phase difference;
• and
• (f) means for summing said output signal and said phase signal to produce a phase and frequency difference signal representing the phase and frequency difference between the FM signal and the reference signal.

A method for demodulating an FM signal comprising the steps of:

• (a) generating a reference signal;
• (b) generating a cyclical signal having a repeated series of sequential nonambiguous states, said cyclical signal being generated in synchronism with said FM signal;
• (c) sampling the state of said cyclical signal in synchronism with said reference signal;
• (d) comparing the current sampled state of said cyclical signal with the immediate preceding sampled state of said cyclical signal to detect a change of state;
• and
• (e) generating an output signal when said change of state is detected.

A method for measuring the phase and frequency difference between an FM signal and a reference signal comprising the steps of:

• (a) generating a cyclical signal having a recurring series of nonambiguous states, said cyclical signal generated in synchronism with the FM signal;
• (b) sampling the state of said cyclical signal in synchronism with the reference signal and storing the present and immediately preceding sampled states of said cyclical signal;
• (c) detecting a state change between said stored sampled states and detecting the direction of state change, said state change indicating a frequency difference between said FM signal and said reference signal;
• (d) generating an output signal when a state change is detected, said output signal indicating said direction of state change;
• (e) measuring the phase difference between said FM signal and said reference signal and generating a phase signal proportional to said phase difference;
• and
• (f) summing said output signal and said phase signal to produce a phase and frequency difference signal proportional to the phase and frequency difference between the FM signal and the reference signal.