| 摘要 |
The phase and/or period stability of a device being tested is determined by connecting the device in one orthogonal arm of a phase detector having a mixer. In the other arm is an adjustable, variable phase shift device, such as a line stretcher. The output of the mixer is fed through an active low pass filter to derive a DC voltage indicative of the phase shift of the tested device. Initially, the variable phase device is adjusted so that the DC voltage is approximately zero to nullify the phase shift of the tested device under normal conditions. The DC voltage level is converted into a time interval indicative of the phase change of the tested device by determining when the level equals the amplitude of a low frequency ramp voltage that functions similar to a beat frequency output of a prior art dual mixer detector. The interval between adjacent equality points for the phase indicating voltage and the ramp voltage can be measured or the period between a reference point on the ramp voltage and the equality between the ramp voltage and the phase indicating voltage can be measured.
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