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Abstract

An automatic phase compensation circuit is disclosed for use with carrier transducers. A quadrature oscillator drives the carrier transducer and provides phase reference and quadrature reference signals to a phase shifter. The phase shifter provides phase shifted reference signals. The return signal from the carrier transducer is separately demodulated with respect to each of the phase shifted reference signals. The demodulated signal with respect to the phase shifted quadrature reference signal is converted into a DC control signal which controls the amount of the phase shift of the phase shifter. The phase shifter receives the quadrature reference signal into a variable gain amplifier controlled by the DC control signal. The output of the variable gain amplifier is summed with the phase reference signal. The resultant summation is a phase shifted reference signal with the control signal controlling the amount of phase shift. The phase shifter reference signal is fed into a constant gain amplifier which outputs the phase shifted phase reference signal. A 90.degree. phase shifter generates a phase shifted quadrature reference signal. The return signal demodulated with respect to the phase shifted phase reference signal will be the full magnitude of the return signal independant of the phase shift of the carrier transducer.

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