Precision digital pulse phase generator

A timing generator, comprising:

• a crystal oscillator connected to a flip-flop and providing for a square-wave reference clock;
• a first series connected chain of inverters connected to said square-wave reference clock and providing for a timing reference output signal;
• a resistor-capacitor combination having a first resistor connected to said square-wave reference clock, a second resistor connected to receive a voltage control signal, and a capacitor connected across an output;
• a second series connected chain of inverters connected to said output of the resistor-capacitor combination and providing for a variable delay output signal;
• a first logic gate having a pair of inputs connected between a part of the second series connected chain of inverters and said flip-flop and providing for a variable duty-cycle pulse signal having a constant frequency fixed by the crystal oscillator;
• an op-amp having a first summing junction connected through a first integration resistor to the first logic gate and an output connected to provide said voltage control signal to the resistor-capacitor combination according to a difference in currents injected into said first summing junction;
• and
• a digital-to-analog converter (DAC) connected to inject a setpoint current into said first summing junction in linear relationship to a digital control code input signal;
• wherein said digital control code provides for a linear control of the delay of said variable delay output signal compared to said square-wave reference clock.

A method for digitally controlling the phase delay between a reference clock and a sample clock, the method comprising the steps of:

• generating a reference frequency;
• generating a sampling frequency having the same frequency of said reference frequency but separated in phase;
• generating a fixed-frequency variable-duty-cycle pulse signal from said sampling frequency with a duty cycle that varies linearly with said phase difference between said sampling frequency and said reference frequency;
• integrating said variable-duty-cycle pulse signal to yield a first current proportional to the duty cycle of said variable-duty-cycle pulse signal;
• converting a digital control code into a control current connected to add to or subtract from said first current;
• and
• producing a control voltage connected to affect said phase difference between said sampling frequency and said reference frequency;
• wherein said digital control code provides for a linear control of the phase difference between said sampling frequency and said reference frequency.