OVERVIEW

In the last chapter, we considered the design of digital filters based on the approximation methods for analog filters. We investigated a number of ways that the transfer functions in the analog domain could be converted to transfer functions in the digital domain. In this chapter, we will develop methods that deal with the digital filter as a unique filter type, not based on analog filter approximation methods. The focus of this chapter will be on finite impulse response (FIR) filters that have only a finite number of terms in their impulse response. These filters have a number of advantages over the IIR filter types. An FIR filter is always stable, realizable, and provides a linear phase response under specific conditions. These characteristics make FIR filters attractive to many filter designers. However, the major disadvantage of FIR filters is that the number of coefficients needed to implement a specific filter is often much larger than for IIR designs. A more complete comparison of IIR and FIR filters is given in Section 8.1.

We will begin this chapter with a standard method of designing FIR digital filters using the Fourier series description of the desired frequency response. This method will then be modified and improved by using a windowing technique to improve the shape of the responses. In addition, the Parks-McClellan optimization technique will be discussed as a technique of reducing the length of the resultant FIR filters. Finally, the C code for determining the frequency response of FIR filters...