Phase locked demodulator

A circuit for providing a voltage output which depends on the phase difference between a digital input signal corresponding to a frequency modulated signal and a voltage controlled oscillator, comprising:

• Edge pulse making means for producing pulses corresponding to the positive transitions of said input signal;
• Inverting means for inverting said input signal;
• Second edge pulse making means for producing pulses corresponding to the negative transitions of said input signal;
• Digital means defining a set-reset flip-flop having its set input connected fto the output of said first edge pulse making means to produce an output thereoutof which directly corresponds to positive excursions of said digital input signal;
• Second digital means defining a set-reset flip-flop having its set input connected to the output of said second edge pulse making means to produce an output thereoutof which directly corresponds to negative excursions of said digital input signal;
• Switch means defining diodes in pairs and having separate current sources connected to the outputs of said first and second digital means to route a comparison current in accordance with the output of said first and second digital means;
• Amplifier means defining an operational amplifier connected to the output of said switch means for amplifying said comparison of said switch means;
• Voltage controlled oscillator means connected to the output of said amplifier means to provide an output thereoutof having two stable states, said states being 180.degree. out of phase with said digital input signal in accordance with said amplified comparison signal;
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• third edge pulse making means connected to the output of said voltage controlled oscillator and the reset input of said first set-reset flip-flop means for producing pulses thereoutof which correspond to the positive excursions of said voltages controlled oscillator output square wave to change the state of said first flip-flop output;
• second inverter means connected to the output of said voltage controlled oscillator to provide thereoutof an output signal 180.degree. of phase with said voltage controlled oscillator output;
• and
• fourth edge pulse making means connected between the output of said second inverter means and the reset input of said second set-reset flip-flop means for producing pulses thereoutof which correspond to the negative excursions of said voltage controlled oscillator output square wave to change the state of said second flip-flop output.