Linear noise reduction for a test and measurement system

Patent metadata

Field	Value
Publication number	US-2017292977-A1
Application number	US-201715476676-A
Country	US
Kind code	A1
Filing date	Mar 31, 2017
Priority date	Apr 8, 2016
Publication date	Oct 12, 2017
Grant date	—

Abstract

Disclosed is a mechanism for reducing noise caused by an analog to digital conversion in a test and measurement system. An adaptive linear filter is generated based on a converted digital signal and measured signal noise. The adaptive linear filter includes a randomness suppression factor for alleviating statistical errors caused by a comparison of a signal circularity coefficient and a noise circularity coefficient in the adaptive linear filter. The adaptive linear filter is applied to the digital signal along with a stomp filter and a suppression clamp filter. The digital signal may be displayed in a complex frequency domain along with depictions of the adaptive linear filter frequency response and corresponding circularity coefficients. The display may be animated to allow a user to view the signal and/or filters in the frequency domain at different times.

First claim

We claim:

1 . A test and measurement system comprising:
an analog to digital (A/D) converter to produce a digital signal from an analog signal, the digital signal including channel noise introduced by the A/D converter; a waveform memory, coupled with the A/D converter, to store the digital signal; and a processor, coupled with the waveform memory, to:
convert the digital signal into a complex frequency domain by applying a time-frequency transform to the digital signal,
determine a signal circularity coefficient for the digital signal and a noise circularity coefficient for the channel noise,
generate frequency domain coefficients for an adaptive linear filter through a comparison of the signal circularity coefficient and the noise circularity coefficient, and
apply the adaptive linear filter to the digital signal to reduce the channel noise from the digital signal.

2 . The test and measurement system of claim 1 , wherein the comparison of the signal circularity coefficient and the noise circularity coefficient includes an application of a randomness suppression factor to reduce statistical errors caused by the comparison.

3 . The test and measurement system of claim 1 , wherein the processor is further to apply a suppression clamp to results from the adaptive linear filter, the suppression clamp to reduce statistical errors at a Nyquist frequency of the A/D converter.

4 . The test and measurement system of claim 1 , wherein the processor is further to apply a bandwidth stomp filter to results from the adaptive linear filter, the bandwidth stomp filter to remove channel noise from the digital signal above a specified frequency.

5 . The test and measurement system of claim 1 , wherein the adaptive linear filter to reduce the channel noise is further applied by determining a signal variance for the digital signal and a noise variance for the channel noise.

6 . The test and measurement system of claim 5 , wherein the frequency domain coefficients for the adaptive linear filter are further generated by comparing the signal circularity coefficient and the noise circularity coefficient to the signal variance and the noise variance.

7 . The test and measurement system of claim 1 , wherein a mean value of the digital signal and a mean value of the channel noise are removed prior to applying the time-frequency transform, and the mean value of the digital signal is added back to results from the adaptive linear filter.

8 . A computer readable storage medium having instructions stored thereon that, when executed by a processor of a test and measurement system, cause the test and measurement system to:
convert a digital signal into a complex frequency domain by applying a time-frequency transform to the digital signal, the digital signal including channel noise introduced by an analog to digital (A/D) converter that produced the digital signal; determine a signal circularity coefficient for the digital signal and a noise circularity coefficient for the channel noise; generate frequency domain coefficients for an adaptive linear filter through comparison of the signal circularity coefficient and the noise circularity coefficient through application of a randomness suppression factor for reduction of statistical errors caused by the comparison of the signal circularity coefficient and the noise circularity coefficient; and apply the adaptive linear filter to the digital signal to reduce the channel noise from the digital signal.

9 . The computer readable storage medium of claim 8 , wherein the adaptive linear filter for reducing the channel noise is further applied by determining a signal variance for the digital signal and a noise variance for the channel noise.

10 . The computer readable storage medium of claim 9 , wherein the signal variance for the digital signal and the noise variance for the channel noise are determined according to:
Φ v ( m )= E[|V ( n,m )| 2 ] and Φ y ( m )= E[|Y ( n,m )| 2 ],
where Φ v (m) is the noise variance at an index m, E[ ] are expected values of the variance, V (n,m) is frequency domain channel noise in an n by m sized matrix of data stored for application of the time-frequency transform, Φ y (m) is the signal variance at an index m, and Y(n,m) is frequency domain digital signal data in an n by m sized matrix of data stored for application of the time-frequency transform.

11 . The computer readable storage medium of claim 8 , wherein the signal circularity coefficient and the noise circularity coefficient are determined according to:

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Assignees

• Tektronix Inc

Inventors

• Pickerd John J
• Tan Kan

Classifications

• H03H2021/0098

  Adaptive filters comprising analog and digital structures · CPC title

• H03H21/00

  Adaptive networks · CPC title

• H03M1/0626

  by filtering · CPC title

• H03H21/0012

  Digital adaptive filters · CPC title

• H03M1/08

  of noise {(H03M1/0617 takes precedence)} · CPC title