Suppressed carrier based PM and AM noise measurement techniques

The purpose of this paper is to discuss the advantages and disadvantages of using carrier suppression techniques to measure PM and AM noise in oscillators, amplifiers, and components. Carrier suppression was first introduced by Klaus H. Sann in 1968 to measure noise in amplifiers. The major advantages of these configurations over conventional measurements is that the noise contribution of the phase or amplitude detector is reduced by the degree of carrier suppression until the thermal noise limit is reached. This typically results in an improvement of 10-60 dB in the noise floor. The advantages over the three-cornered-hat cross-correlation technique is that the same or better results can be obtained in real time instead of having to wait for a large number of averages. The disadvantage is that this approach does not work as well as conventional approaches for measuring AM noise in sources. Three-cornered-hat techniques used with conventional mixer-based system or carrier suppressed systems are required to obtain an unbiased estimate of the PM noise in state-of-the-art sources. Suppressed carrier techniques can also be used to reduce the contribution of the phase detector in some specialized oscillator configurations.

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