Kollmorgen AKD PDMM series, User Manual

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AKD PDMM User Guide | 12.3.6.1 Types of Anti-Resonance Filters
Biquad
A biquad is a flexible filter that can be thought up as being made up of two simpler filters; a zero (numer-
ator) and a pole (denominator). In fact, the pre-defined filters mentioned above are really just special cases
of the biquad.
Both the zero (numerator) and the pole (denominator) have a flat frequency response at low frequencies
and a rising frequency response at high frequencies. The transition frequency and damping must be spec-
ified for both the numerator and denominator.
Analyzing the numerator and denominator, the frequency response calculation is simple:
If the numerator and denominator are plotted in dB, the biquad response is numerator – denominator.
Understanding how the numerator and denominator work is crucial in understanding how a biquad
frequency response is created.
Below is an example of a biquad filter similar to a Lead Lag filter type. To help understand how to deter-
mine the frequency response of the biquad, the numerator and denominator response have been plotted. If
the denominator is subtracted from the numerator, the biquad response is the result.
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