PSK Demodulator with automatic compensation of delay induced phase shifts

A method for automatically compensating for phase variations in the delay element of a differentially coherent PSK signal demodulator, consisting essentially of the steps of:

• splitting the signal to be demodulated into first and second portions;
• delaying the first portion but not the second portion of the signal;
• and
• automatically adjusting the phase of the second portion but not the first portion to maintain a fixed component of phase differential between the delayed first portion and the adjusted second portion.

A method for automatically compensating for phase variations in the delay element of a coherent PSK signal demodulator, comprising the steps of:

• splitting the signal to be demodulated into a first and a second portion;
• delaying the first portion but not the second portion of the signal;
• shifting in a variable manner the phase of the second portion but not the first portion;
• obtaining the PSK-modulation-independent phase difference between the delayed first portion and shifted second portion;
• and
• maintaining said phase difference constant by using said obtained phase difference to control said shifting via a feedback loop.

A differential phase correction loop that is non-responsive to phase shift modulation, comprising:

• a first signal source producing a first signal of the form sin (WT+PJ+PD) where W is the frequency, T is the time, PJ is a modulation phase shift, and PD is a phase variation introduced by a delay element;
• a variable phase shifter having a first input, a control input, and an output signal of the form sin (WT+PI+PS) where PI is a modulation phase shift and PS is a phase shift introduced by the shifter;
• and
• a phase tracking circuit having a first input connected to the first signal source, a second input connected to the output signal of the variable phase shifter, and an output connected to the control input of the variable phase shifter;
• wherein the phase tracking circuit produces a signal which isolates the difference between PS and PD, is independent of PI and PJ, and controls PS via the variable phase shifter so as to maintain a fixed phase differential between PS and PD.

A phase shift keyed signal demodulator comprising:

• a first splitter having as an input the signals to be demodulated;
• a delay means having an input connected to a first output of the first splitter;
• a second splitter having an input connected to an output of the delay means;
• a variable phase shifter having a first input connected to a second output of the first splitter;
• a third splitter having an input connected to an output of the variable phase shifter;
• a first mixer having a first input connected to a first output of the second splitter and having a second input connected to a quadrature output of the third splitter;
• a first low pass filter having an input connected to an output of the first mixer and having as an output the demodulated signals;
• a fourth splitter having an input connected to a second output of the second splitter;
• a fifth splitter having an input connected to an inphase output of the third splitter;
• a second mixer having a first input connected to a first output of the fourth splitter and having a second input connected to a quadrature output of the fifth splitter;
• a third mixer having a first input connected to a second output of the fourth splitter and having a second input connected to an inphase output of the fifth splitter;
• a second low pass filter having an input connected to an output of the second mixer;
• a third low pass filter having an input connected to an output of the third mixer;
• a multiplier having a first input connected to an output of the second low pass filter and having a second input connected to an output of the third low pass filter;
• and
• a conditioning amplifier having an input connected to an output of the multiplier and having an output connected to a second input of the variable phase shifter.