IIR Bandpass Filters Using Cascaded Biquads
In an earlier post [1], we implemented lowpass IIR filters using a cascade of second-order IIR filters, or biquads. This post provides a Matlab function to do the same for Butterworth bandpass IIR filters. Compared to conventional implementations, bandpass filters based on biquads are less sensitive to coefficient quantization [2]. This becomes important when designing narrowband filters.
Summary
This blog post shows how to implement Butterworth bandpass IIR filters as a cascade of second-order sections (biquads) and provides a MATLAB function to do so. It explains why cascaded biquads reduce sensitivity to coefficient quantization and demonstrates design choices useful for narrowband bandpass filters in practical systems.
Key Takeaways
- Implement a Butterworth bandpass as a cascade of biquads (second-order sections) using the provided MATLAB function.
- Evaluate and mitigate coefficient quantization effects to improve numerical robustness for narrowband filters.
- Design and parameterize narrowband bandpass filters to meet passband/stopband specifications while preserving stability.
- Scale and cascade biquads properly to minimize overflow and maintain filter performance in fixed-point implementations.
Who Should Read This
Intermediate DSP engineers or researchers who use MATLAB and need robust narrowband bandpass filter implementations for communications, radar, or audio applications.
Still RelevantIntermediate
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