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Bilinear Transformation Made Easy

Bilinear Transformation Made Easy

Peter J. Pupalaikis
TimelessIntermediate

A formula is derived and demonstrated that is capable of directly generating digital filter coefficients from an analog filter prototype using the bilinear transformation. This formula obviates the need for any algebraic manipulation of the analog prototype filter and is ideal for use in embedded systems that must take in any general analog filter specification and dynamically generate digital filter coefficients directly usable in difference equations.


Summary

This paper derives a closed-form formula that directly generates digital IIR filter coefficients from an analog prototype using the bilinear transformation, removing the need for manual algebraic manipulation. It demonstrates the method, addresses frequency prewarping and implementation considerations, and highlights suitability for embedded real-time systems that must produce coefficients dynamically for difference-equation implementations.

Key Takeaways

  • Apply a single closed-form formula to compute digital IIR coefficients directly from an analog prototype using the bilinear transform.
  • Avoid manual algebraic re-derivation of analog prototypes by feeding specifications into the formula and obtaining coefficients ready for difference equations.
  • Incorporate frequency prewarping and pole-zero mapping guidance to preserve frequency response when converting from s-domain to z-domain.
  • Implement the method in embedded or real-time DSP environments to dynamically generate coefficients for on-the-fly filter creation.
  • Account for practical issues such as coefficient scaling and fixed-point quantization for stable runtime implementations.

Who Should Read This

DSP engineers and embedded systems developers with experience in filter design who need a practical, implementable method to convert analog prototypes to digital IIR coefficients for real-time applications.

TimelessIntermediate

Topics

Filter DesignReal-Time DSP

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