Ten Essential Skills for Electrical Engineers

8

HOW TO DESIGN DIGITAL FILTERS

If your design requires a filter, and if the filter can be implemented in an existing field programmable gate array (FPGA) or microprocessor, then its effect on the product cost will be much less than if the filter were implemented using dedicated components such as capacitors, inductors, or op-amps. In addition, the design will be more reliable and smaller because it will have fewer components. Finally, it will not be affected by manufacturing tolerances, temperature, and aging. These advantages are compelling reasons to use digital filters wherever possible.

Digital filtering, or equivalently discrete-time filtering, is usually the best approach if the signal to be filtered can be represented as a set of uniformly spaced samples and a device is available to do the necessary computations. The continuing evolution of analog to digital converters (ADCs) and digital to analog converters (DACs) combined with advances in hardware- and firmware-based digital signal processors (DSPs) makes digital filtering more practical every day. As a working engineer, it is highly likely that you will find yourself designing digital filters or updating older designs to use them.

Designing and debugging any kind of filter is fun and rewarding, but the process is very different for digital and analog filters. A digital filter is designed by selecting an architecture and then computing constants that determine the filter’s bandwidth, cutoff frequency, and so on. Next, ...