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Finite-Q Elements and Predistortion

Finite-Q Elements and Predistortion

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In addition to increased insertion loss, other undesirable features of predistorted networks are a wide range of element values, increased sensitivity to small element-value changes, increased mismatch between the filter's input impedance and the source resistance, and the appearance of passband ripples when the element q is small and differs from the design value. Consequently predistortion should only be used when q is relatively high and the exact response is desired. Otherwise, a more practical solution is the adjustment of the filter's bandwidth to accommodate losses as explained. In most cases the exact response is not a necessity; the lossy response is satisfactory, and the disadvantages associated with the predistortion method are then absent.

Chapter Contents:

  • 6.1 The Quality Factor
  • 6.2 Lossy-Filter Responses
  • 6.2.1 Transfer Function
  • 6.2.2 Transient Responses
  • 6.2.3 Butterworth Filter Analysis
  • 6.2.4 Chebyshev and Gaussian Filter Analysis
  • 6.2.5 Q Requirement for Bandpass Filters
  • 6.2.6 Illustrative Example
  • 6.3 Insertion Loss
  • 6.3.1 Mismatch Loss
  • 6.3.2 Resistive Loss
  • 6.3.3 Insertion Loss Curves
  • 6.3.4 Approximate Expression for Insertion Loss
  • 6.3.5 Minimum Insertion Loss Filter
  • 6.3.6 Insertion Loss Comparison of Various Filters
  • 6.4 Predistortion
  • 6.4.1 Minimum Value of Quality Factor for Various Responses
  • 6.4.2 Insertion Loss
  • 6.4.3 Example of Insertion Loss Calculation
  • 6.4.4 Example of Predistorted Filter Design
  • 6.4.5 Summary
  • References
  • Problems

Inspec keywords: resistors; band-pass filters; distortion

Other keywords: filter input impedance; finite-Q elements; insertion loss; element value; predistorted network; lossy response; passband ripple; source resistance; predistortion method

Subjects: Signal processing theory; Filtering methods in signal processing

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