Applying Multi-Stage, Multi-Rate Digital Filtering

Figure 1: The input signal shows both the desired 63-kHz signal
along with a 60-Hz component. Zoom trace Z1 shows the
60-Hz component in detail.

A while back, we posted some basics on how to apply digital filters to sort out signals with undesirable elements riding on top of them, i.e. a square wave that's being corrupted by a sinusoidal signal creeping in from somewhere in your system design. Now, let's look at how to extend the range of cutoff frequencies for digital filters, allowing them to be used even more effectively.