Anti-Aliasing Filtering

My professional interest has evolved over my career into what may be broadly classified as “measurement” – I like to believe I design measurement instrumentation with a particular focus on transducer interfacing – the portion of the signal chain from physical phenomena to the ADC output. I expand that interest into the phenomena which is to be measured – hence my Ph.D. in electromagnetic geophysics – and the associated power systems. Often overlooked is the effect the power supply has on signal integrity. Power supply rejection decreases with frequency and supply imperfections can distort the signal to be measured.

“Garbage In, Garbage Out” (GIGO) is still a truism: if the information is distorted before it is digitized, later interpretation of the data may be misleading and there is often no way to “fix” it later with numerical methods.

However, my focus with this discussion is the anti-aliasing filter.

A basic signal path might be represented in a form similar to:

I’ll be looking into the “Amplifier/Filter” block. Although shown as a single block – because the filter is typically incorporated into a gain stage – I want to examine the mathematical representation of ideal filters. Such a discussion is applicable to both passive and active filters … and either can cause undesired effects on signal integrity.

So let’s get to it.