Distortion Measurements

Distortion Measurements

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The preceding discussion was oriented toward understanding and measuring distortion in the device under test. However, the internal circuits of the analyzer are imperfect and will also produce distortion products. The distortion performance of the analyzer is specified by the manufacturer, either directly or lumped into a dynamic range specification. The instrument user can stretch the performance of the analyzer by understanding the nature of these distortion products. As shown in this chapter, distortion products can be reduced in amplitude by reducing the signal level. Not only do the absolute levels of the distortion products decrease, they decrease more than the decrease in signal level. So as the signal level decreases, the relative distortion level also decreases, depending on the order of the distortion product. Higher-order distortion products decrease the fastest. This implies that the distortion products internal to the analyzer can be reduced by reducing the signal level into the analyzer. The internal input attenuators of the analyzer may be used or an external attenuator may be attached, improving the distortion measurement range of the analyzer. The most obvious disadvantage of reduced signal level is reduced signal-to-noise ratio. The user may find that the low-level distortion products are buried in the noise. Reducing the resolution bandwidth of the analyzer will reduce the measured noise, but at the expense of a slower sweep rate.

Chapter Contents:

  • 7.1 The Distortion Model
  • 7.2 Single-Tone Input
  • 7.3 Two-Tone Input
  • 7.4 Higher-Order Models
  • 7.5 The Intercept Concept
  • 7.6 Harmonic Distortion Measurements
  • 7.7 Use of Low-Pass Filter on Source
  • 7.8 lntermodulation Distortion Measurements
  • 7.9 Distortion Internal to the Analyzer
  • References

Inspec keywords: distortion measurement; noise measurement

Other keywords: resolution bandwidth reduction; dynamic range specification; distortion measurement; higher-order distortion product; internal input attenuator; signal-to-noise ratio; internal circuit; noise measurement

Subjects: Electric noise and interference measurement

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