An improved phase indicator measures the phase difference between a sinusoidal reference signal and a shaped signal having the same frequency. Means are provided for generating a first pulse which begins when the shaped signal makes a positive going transition past a selected voltage level, and ends when the reference signal makes a positive going transition past the zero reference level. A second pulse begins at the end of the first pulse, and ends when the shaped signal makes a negative transition past the selected level. The relative phase of the two signals are adjusted until the first and second pulses are the same length, which occurs when the two signals are 90 degrees out of phase. An indicator is then calibrated to read 90 degrees, and thereafter indicates the correct phase relationship between the two signals.
Morton E. Brown