Cross-Spectrum PM Noise Measurement, Thermal Energy, and Metamaterial Filters

This article is intended to give a warning about: (i) the internal processing inside the phase-noise analyzers, (ii) the oscillators whose white phase noise floor seems too low, chiefly the 100-MHz OCXOs, and (iii) the need to introduce in the domain of phase-noise measurements the basic concepts of uncertainty found in the International Vocabulary of Metrology (VIM).The measurement of low-noise quartz oscillators, or of other lownoise oscillators exhibiting a noise floor of the order of −180 dBc/Hz or less, relies on the cross-spectrum method. The measurement may take long time, from hours to 1-2 days, for the number of averaged cross spectra to be sufficient to reject the background of the noise analyzer. That said, something anomalous is often seen in a region approximately one decade wide, located where higher-slope noise joins the white floor or the 1/f noise. The plot may be quite thick and irregular, and a dip may appear, where the phase noise looks lower than the white noise floor. Such anomalies reveal something worse. The white region of the PM noise spectrum may be affected by gross errors and, in the not-so-rare worst case, is a total nonsense. We address the problem trough a simple experiment, where we insert a dissipative attenuator between the oscillator and the PN analyzer. Surprisingly, in some cases the attenuation results in a lower noise floor. Such erratic behavior is reproducible, having been observed separately in three labs with instruments from the two major brands. We provide the experimental evidence, the full theory, and suggestions to mitigate the problem.

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“…From the theoretical standpoint, the combined effect of the attenuator (5) and of the power splitter (18) results in…”

Section: Discussionmentioning

confidence: 99%

Artifacts and errors in cross-spectrum phase noise measurements

Gruson

Rus²,

Rohde

et al. 2020

Metrologia

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“…Different options for the power splitter are discussed in [137]. Another perspective on the power splitters is proposed in [138], with original results. In [139], we propose a method for the measurement of the bias error due to both power splitter and internal crosstalk.…”

Section: Limitations Of the Cross-spectrum Methodsmentioning

confidence: 99%

“…Literature of the past ten years [136], [137], [138], [139] and three workshops [140], [141], [142] point to substantial errors and discrepancies in the measurement of commercial oscillators exhibiting very-low phase noise. The concept of null measurement uncertainty applies [44, Entry 4.29], which is the uncertainty in the special case of signal approaching zero.…”

Section: E Metrologist's Perspective Of Phase Noise Uncertaintymentioning

confidence: 99%

The Companion of Enrico’s Chart for Phase Noise and Two-Sample Variances

Rubiola

Vernotte

2023

IEEE Trans. Microwave Theory Techn.

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Phase noise and frequency (in)stability both describe the fluctuation of stable periodic signals from somewhat different standpoints. Frequency is unique compared to other domains of metrology, in which its fluctuations of interest span at least 14 orders of magnitude, from 10 −4 in a mechanical watch to 10 −18 in atomic clocks. The frequency span of interest is some 12-15 orders of magnitude from μHz to GHz Fourier frequency for phase noise, while the time span over which the fluctuations occur ranges from sub-μs to years integration time for variances. Because this domain is ubiquitous in science and technology, a common language and tools suitable to the variety mentioned are a challenge. This article is at once: 1) a tutorial; 2) a review covering the most important facts about phase noise, frequency noise, and two-sample (Allan and Allan-like) variances; and 3) a user guide to "Enrico's Chart of Phase Noise and Two-Sample Variances." In turn, the Chart is a reference card collecting the most useful concepts, formulas, and plots in a single A4/A-size sheet, intended to be a staple on the desk of whoever works with these topics. The Chart is available under Creative Commons 4.0 CC-BY-NC-ND license from Zenodo,

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“…This is sometimes untrue, and anyway hard to check. Gross errors are possible if the experimentalist has not a deep understanding (see, for example [33], [34]). The second problem is the measurement time, chiefly with the digital instruments because the noise of the DACs under test is often lower than that of the input ADCs.…”

Section: Principles and Methodsmentioning

confidence: 99%

Phase-Noise and Amplitude-Noise Measurement of DACs and DDSs

Calosso

Olaya

Rubiola

2019

2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC)

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This article proposes a method for the measurement of Phase Noise (PN, or PM noise) and Amplitude Noise (AN, or AM noise) of Digital-to-Analog Converters (DAC) and Direct Digital Synthesizers (DDS) based on modulation-index amplification. The carrier is first reduced by a controlled amount (30-40 dB) by adding a reference signal of nearly equal amplitude and opposite in phase. Then, residual carrier and noise sidebands are amplified and sent to a conventional PN analyzer. The main virtues of our method are: (i) the noise specs of the PN analyzer are relaxed by a factor equal to the carrier suppression ratio; and, (ii) the capability to measure the AN using a PN analyzer, with no need for the analyzer to feature AN measurement. An obvious variant enables AN and PN measurements using an AN analyzer with no PN measurement capability. Such instrument is extremely simple and easy to implement with a power-detector diode followed by a FFT analyzer. Unlike the classical bridge (interferometric) method, there is no need for external line stretcher and variable attenuators because phase and amplitude control is implemented in the device under test. In one case (AD9144), we could measure the noise over 10 decades of frequency. The flicker noise matches the exact 1/f law with a maximum discrepancy of ±1 dB over 7.5 decades. Thanks to simplicity, reliability, and low background noise, this method has the potential to become the standard method for the AN and PN measurement of DACs and DDSs.

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Cross-Spectrum PM Noise Measurement, Thermal Energy, and Metamaterial Filters

Cited by 14 publications

References 27 publications

Artifacts and errors in cross-spectrum phase noise measurements

Artifacts and errors in cross-spectrum phase noise measurements

The Companion of Enrico’s Chart for Phase Noise and Two-Sample Variances

Phase-Noise and Amplitude-Noise Measurement of DACs and DDSs

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