The Measurement of AM noise of Oscillators

Abstract

The close-in AM noise is often neglected, under the assumption that it is a minor problem as compared to phase noise. With the progress of technology and of experimental science, this assumption is no longer true. Yet, information in the literature is scarce or absent.This report describes the measurement of the AM noise of rf/microwave sources in terms of Sα(f ), i.e., the power spectrum density of the fractional amplitude fluctuation α. The proposed schemes make use of commercial power detectors based on Schottky and tunnel diodes, in single-channel and correlation configuration.There follow the analysis of the front-end amplifier at the detector output, the analysis of the methods for the measurement of the powerdetector noise, and a digression about the calibration procedures.The measurement methods are extended to the relative intensity noise (RIN) of optical beams, and to the AM noise of the rf/microwave modulation in photonic systems.Some rf/microwave synthesizers and oscillators have been measured, using correlation and moderate averaging. As an example, the flicker noise of a low-noise quartz oscillator (Wenzel 501-04623E) is Sα = 1.15×10 −13 /f , which is equivalent to an Allan deviation of σα = 4×10 −7 . The measurement systems described exhibit the world-record lowest background noise.

Oscillator AM-to-FM noise conversion due to the dynamic frequency-drive sensitivity of the crystal resonator

“…In order to predict the possible effect of AM-to-FM noise conversion in a crystal oscillator resulting from the resonator frequency-drive sensitivity, the author created the Excel spreadsheet shown in Figure 1. In the Figure 1 spreadsheet, data was entered for the SC-cut crystal of Table 1 Referring again to the paper by Enrico Rubiola that included results of measurement of crystal oscillator AM noise, the first two columns in Table 3 summarizes the results of that author's measurement of the AM noise of several 100MHz crystal oscillators manufactured by Wenzel Associates [10]. The third column in the table shows the level of the AM noise-induced, FM noise that would occur under the (worst-case) assumption of relatively low (50 ohm) crystal resistance, relatively high (5milliwatt) crystal dissipation, and 31ppb/mA 2 dynamic, frequency-drive sensitivity coefficient in the crystal (the value reported by Horton and Hague).…”

“…Using results of measurement of commercial VHF crystal oscillator AM noise reported in separate papers by Rubiola [10] and Nelson,et. al.…”

The effect of AM noise on correlation phase-noise measurements

“…Unfortunately, little information on AM noise is available (see Ref. [Rub05]). A careful analysis of the correlation schemes is necessary to understand the effect of AM noise and when it can be reduced or eliminated.…”

Extended Noise Analysis Model of CW-type Radar Sensors with IQ Down-Conversion

“…In [18], [19], descriptions of simultaneous amplitude and phase noise measurement are presented. In [23], a more precise amplitude noise measurement method can be found.…”

“…The PSD of noise, caused by LO amplitude noise for components I and Q, is formed according to (23) and (24), respectively:…”