Efficient Digital Fiilters
What would you do in the following situation? Let ’ s say you are diagnosing a DSP system problem in the field. You have your trusty laptop with your development system and an emulator. You figure out that there was a problem with the system specifications and a symmetric FIR filter in the software won ’ t do the job; it needs reduced passband ripple, or maybe more stopband attenuation. You then realize you don ’ t have any filter design software on the laptop, and the customer is getting angry. The answer is easy: You can take the existing filter and sharpen it. Simply stated, filter sharpening is a technique for creating a new filter from an old one [1] – [3] . While the technique is almost 30 years old, it is not generally known by DSP engineers nor is it mentioned in most DSP textbooks.
Summary
This paper presents practical filter-sharpening techniques that let an engineer improve an existing symmetric FIR filter's passband ripple and stopband attenuation without running a full redesign. It explains the theory behind sharpening transforms, shows how to evaluate improvements via spectral analysis, and gives implementation guidance for constrained, field-deployable DSP systems.
Key Takeaways
- Apply filter-sharpening transforms to an existing symmetric FIR to reduce passband ripple or increase stopband attenuation without redesigning coefficients from scratch.
- Use polynomial and cascaded sharpening structures to achieve desired frequency-response improvements with minimal extra computation.
- Evaluate sharpened-filter performance using FFT-based spectral analysis to quantify changes in ripple, attenuation, and transition band.
- Implement sharpened filters in fixed-point/real-time targets while managing coefficient quantization and computational cost.
Who Should Read This
Intermediate DSP engineers and field developers who must quickly improve deployed FIR filter performance (audio, communications, radar) without access to full filter-design tools.
Still RelevantIntermediate
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