High-resolution measurement of phase shifts in high frequency phase modulators

An integrated circuit comprising:

• a frequency synthesizer for generating a first signal of a desired frequency;
• a phase modulator connected to receive the first signal and for generating a second signal having the same frequency as the first signal but shifted in phase to the first signal;
• a phase to duty-cycle converter for receiving the first and second signals and for generating an output signal having a duty-cycle that is a function of the difference in phase between the first and second signals;
• and
• a lowpass filter for converting the output of the phase to duty-cycle converter to a direct current signal having an amplitude proportional to the difference in phase between the first and second signals.

A system for measuring the phase difference between two signals comprising:

• an integrated circuit including
• a phase modulator receiving a reference signal and generating a phase shifted version of the reference signal;
• and
• a phase to duty-cycle converter arranged to receive the reference signal and the phase shifted version of the reference signal, the phase to duty-cycle converter outputting a signal based on the reference signal and the phase shifted version of the reference signal, the output signal having a duty-cycle that is a function of a phase difference between the reference signal and the phase shifted version of the reference signal;
• and
• a digital volt meter for measuring the direct current (DC) voltage level of the output signal;
• wherein the phase difference between the reference signal and the phase shifted version of the reference signal is a function of the voltage level measured by the digital volt meter divided by a peak voltage of the output signal.

A method for measuring the phase difference between two signals comprising:

• shifting a phase of a first signal to form a second signal;
• generating a third signal having a duty-cycle that is a function of the phase difference between the first and second signals;
• low-pass filtering the third signal;
• measuring the amplitude of the low-pass filtered third signal;
• and
• calculating the phase difference between the first and second signals based on the measured amplitude.