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.

Suppressed carrier based PM and AM noise measurement techniques

The authors report on measurements of phase modulation (PM) and amplitude modulation (AM) noise in a variety of amplifiers, dielectric resonator oscillator (DRO) sources, and mixers at 10.6 GHz. Two-channel measurement systems and cross-correlation analysis were used. In amplifiers there are at least two random noise processes that generate equal levels of PM and AM noise when the amplifier is in the linear operating range. The noise processes correspond to a flicker noise process and a white noise process. In the DRO sources these noise mechanisms are shown to be present in the active components and determine the AM and PM characteristics of the oscillator. A noise model for oscillators incorporating Leeson's PM noise model and a model for AM noise in which the active components have two common random noise processes are proposed. The authors report AM noise levels of 140 dB below the PM levels at 1 Hz and typical noise floors of -169 dBc/Hz at 10 MHz. Noise residuals in mixers from three different companies are reported. Typical 1 Hz intercepts vary from -110 to -127 dBc/Hz. Noise floors are typically /spl sim/-173 dBc/Hz. >

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Investigations of AM and PM noise in X-band devices

We demonstrate regenerative divide-by-two (halver) circuits with very low phase modulation (PM) noise at input frequencies of 18.4 GHz and 39.8 GHz. The PM noise of the 18.4 to 9.2 GHz divider pair was L(10 Hz)=-134 dB below the carrier in a 1 Hz bandwidth (dBc/Hz) and L(10 MHz)=-166 dBc/Hz, and the PM noise of the 39.8 GHz to 19.9 GHz divider pair was L(10 Hz)=-122 dBc/Hz and L(10 MHz)=-167 dBc/Hz.

Microwave regenerative frequency dividers with low phase noise

During this, the NIST Centennial Year, I look back on the first 100 years and summarize NIST work on time and frequency measurement, a topic of some prominence from the early years of the institution. Initial work at NIST (then NBS, the National Bureau of Standards) focused primarily on frequency standards needed to support the control of broadcast frequencies in the early days of radio. The Time and Frequency Division was not created until 1967, by which time a number of primary atomic frequency standards had already been developed, and it was clear that a broader program in this field was needed. This paper describes a variety of programs including the development of primary frequency standards, the international coordination of standards, statistical techniques for characterizing noise, dissemination methods, and methods for measuring optical frequency.

Time and frequency measurement at NIST: the first 100 years

Experimental measurements supported by a simple model show that the upper and lower phase modulation (PM) noise sidebands are always equal and 100% correlated, independent of the noise power originating from multiplicative or additive processes. Similarly, we show that the upper and lower amplitude modulation (AM) noise sidebands are also equal and 100% correlated, independent of the noise power originating from multiplicative or additive processes, Moreover, the single sideband (SSB) PM noise is always equal to one-half the total PM noise. The same is true for the AM noise. Although the upper and lower PM or AM noise sidebands are equal and correlated for broadband additive noise, the phase between the AM and the PM sidebands varies randomly with time. These conclusions still hold even when the RF noise sidebands are not symmetric about the carrier.

Correlation between upper and lower sidebands

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor S/sub phi / (10 kHz) of the standard for PM noise measurements is less than -190 dBC relative to 1 rad/sup 2//Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately -130+or-0.2 dB relative to 1 rad/sup 2//Hz (for Fourier frequencies from approximately 1 Hz to 10% of the carrier frequency) is used to evaluate the accuracy versus Fourier frequency. Similar PM/AM noise standards are under test at 10 GHz. This new standard can also be used as an alternative to the normal method of calibrating the conversion sensitivity of the PM/AM detector for PM/AM measurements. Some types of time-domain measurement equipment can also be calibrated. >

Secondary standard for PM and AM noise at 5, 10, and 100 MHz

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +or-0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor of the standard for PM noise measurements is less than -190 dBC rel to 1 rad/sup 2//Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately-130+or-0.2 dB rel to 1 rad/sup 2//Hz is used to evaluate the accuracy versus Fourier frequency. This standard can also be used as an alternative to the normal method of the PM/AM detector for PM/AM measurements. >

F.L. Walls

Papers

Secondary standard for PM and AM noise at 5, 10, and 100 MHz

Secondary standard for PM and AM noise at 5, 10, and 100 MHz