Why High-Q IIR Notch Filters Become Unstable in Real DSP Systems (And How to Fix It)
Introduction IIR notch filters are widely used to suppress narrowband interference due to their efficiency and sharp frequency selectivity. However, engineers frequently encounter instability when pushing notch bandwidths extremely narrow—commonly referred to as high-Q designs. Symptoms include: unexpected oscillations amplification instead of attenuation drifting frequency response sensitivity to coefficient quantization This article explains the physical and numerical reasons behind high-Q notch instability and outlines deterministic design practices that prevent it. ...