ABSTRACT
The notion of “phase” is usually associated with periodic or repeating signals. With these signals, the waveshape perfectly repeats itself every time the period of repetition elapses. The measurement of phase is important in almost all applications where sinusoids proliferate. One of the most obvious measurement techniques is to directly measure the fractional part of the period that has been completed on a cathode-ray oscilloscope. Another approach, which is particularly useful when a significant amount of noise is present, is to take the Fourier transform of the signal. Several techniques are available for the measurement of “relative phase.” One crude method involves forming “Lissajous figures” on an oscilloscope. For high-precision phase measurements and calibration, “phase standard” instruments can be used. These instruments provide two sinusoidal signal outputs, whose phase difference can be controlled with great accuracy. They typically use crystal-controlled timing to digitally synthesize two independent sinusoids with a variable user-defined phase difference.
