| 摘要 |
A noise measurement test system is provided for making phase noise measurements of a unit under test (UUT). The noise measurement test system comprises a variable amplifier, a variable low noise source, a variable phase shifter, a mixer, a variable low noise matching amplifier, analog-to-digital converter, a processor and a spectrum analyzer. A first low noise signal, created by the low noise source, is routed through the unit under test and variable amplifier to the mixer. A second low noise signal, also created by the low noise source, is routed through the variable phase shifter to the mixer. The mixer places the received signals in phase quadrature and outputs a measurement test signal which is routed through an analog-to-digital convertor to the processor and spectrum analyzer. The processor includes control links for adjusting the amplifier, low noise source and phase shifter to ensure that the signals received by the mixer are in phase quadrature. The processor also controls the low noise matching amplifier to ensure that there is proper impedence between the mixer and analog-to-digital convertor, and to ensure that the measurement test signal is of sufficient amplification for proper noise testing. In preferred embodiments, the processor provides for automatic control of the test system through an entire test protocol. In additional preferred embodiments, the noise measurement test system provides for calibration signals which vary in amplitude and frequency relative to a carrier signal.
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