| 摘要 |
A measurement circuit includes two signal sources, one for generating a test input signal to a DUT and the other for generating a sampling signal. Both sources are coupled to one crystal oscillator and one or both sources may be fractional N oscillators. A phase locked loop stabilizes the sampling signal generated by the fractional N oscillator. The test input signal and the output signal from the DUT are separately mixed with the sampling signal and the resulting sampled signal are converted to digital values by A/D converters and stored in a microprocessor. The stored values can later be compared and analyzed by the microprocessor to determine the characteristics of the DUT.
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