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Filtering Applications

Digital filtering offers many advantages over traditional analog filtering methods. Analog filters are generally constructed of a combination of resistors, capacitors, inductors and opamps. For simple filter requirements, an analog filter may be appropriate, but as the complexity of the filter increases, due to performance issues, an analog filter quickly becomes unwieldy.

Digital filters are created by converting an analog input signal into digital samples (numbers) and then performing a whole lot of high speed arithmetic. This is exactly what DSP chips do very well. They are kind of the "Rain Men" in the microprocessor world.

The benefits of digital filtering is that extremely demanding filtering can be performed by just writing a few equations and storing a table of numbers. Digital filters are not affected by aging or temperature variations. If you want to change parameters of analog filter, you might need a soldering iron; with a digital filter you just change the numbers.

This graph is of a digital brickwall filter for a telecom application. It represents just one type of digital filter called a finite impulse response (FIR) filter. In addition, to its superb attenuation characteristics, it also has linear phase. Every Danville DSP product can easily execute this filter.

If you could actually construct an equivalent analog filter, you would need one of the following:

178th Order Butterworth Filter
42nd Order Chebyshev Filter
18th Order Elliptic Filter

If you wanted to correct the phase response as well, you would triple these numbers.