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Technical Papers
Characterizing Digital Audio Transformers with Induced Jitter Histograms

Presented at the Audio Engineering Society Convention, New York December 2001

By Jon D. Paul, Vice President
Scientific Conversion, Inc.

ABSTRACT

Transformers are employed in digital audio systems primarily to reject common mode noise interference. A new test characterizes the interference rejection of a practical transmission system with a transformer at the receiver input. A sample set of the decoded frame sync clocks are accumulated by a statistical time interval analyzer. The analyzer calculates the mean value of the periods, the standard deviation (jitter), and provides a period histogram. The histogram and standard deviation establish a basis for comparing the high frequency interference rejection of various transformers and for quantifying the nature of the induced jitter. Test data are presented for 7 different types of transformers.

Figures

Fig. 1  Transformer Coupled Digital Audio Transmission System

Fig. 2  Common-Mode Noise Rejection

Fig. 3 Effect of Different transformers on CM noise


Fig. 4  test fixture block

Fig 5 Test Fixture Photo

Fig 6 Time Interval Analyzer

Fig. 7 Relationship of observed jitter to system component jitter

Fig. 8 Induced Common-Mode Noise Jitter Comparison

Fig. 9 Typical AES/EBU transformers

Fig. 10 Fig. 18 Jitter Histograms of Various Transformers

Fig. 19 Correlation of Various Transformer Parameters vs Jitter  

Fig. 20 Jt Vs Cps

Fig. 21  Comparison of 7 AES Transformers

Summary and Conclusions

      Induced Interference Testing simulates field conditions

      Commercial transformers exhibit tremendous differences in interference rejection

      AES/EBU receivers exhibit jitter that is function of the transformer CMRR and capacitance

      Professional, broadcast and high resolution applications need maximum CMRR to minimize recovered clock jitter in the presence of noise.

 

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Copyright 2002 Scientific Conversion, Inc. All rights reserved. Information in document is subject to change without notice.

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Last revised: 8 February 2006

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