Design Techniques for FIR Notch Filters

Abstract

Digital notch filters form an integral part of digital signal processing (DSP) used invariably in communication, control, instrumentation and bio medical engineering, to mention a few. They are used to eliminate noise and power line interferences. Digital notch filters can be designed either as an infinite impulse response filter (IIR) or as an finite impulse response filter (FIR). IIR filters have the advantage that they require lower orders for efficient approximation of a given set of specifications. However, IIR filters are potentially not stable and do not provide linear phase characteristics. FIR filters, on the newlinecontrary, are unconditionally stable and can be designed to give exact linear phase newlinecharacteristics. In view of this, the thrust in this research work is on FIR notch newlinefilters. newline newlineIn most of the DSP applications, the interference frequency is not stable. It often varies about a fixed frequency by certain percentage. To remove such interference there can be two options: newline newline1. Design a data dependent filter in which the notch frequencies can be adjusted newlinebased on the input data newline newlineor newline newline2. Design a data independent notch filter with controlled null width that matches newlinewith the expected variable range of the interference.