Spider DSA User’s Manual
312
Figure 178. Filter design shows cutoff frequencies, ripple, band stop attenuation.
In most cases filter design includes making tradeoffs between minimizing the
filter order, ripple, transition band-width, and response time. Not all can be
satisfied at the same time. Filter design can be an iterative process and
experience is helpful.
FIR Real Time Digital Filters
Finite Impulse Response (FIR) filters have an impulse response that lasts for a
finite duration of time. Infinite Impulse Response(IIR) filters have an impulse
response that is infinite in duration. The FIR filter’s finite response is due to a lack
of feedback paths. FIR filters offer several advantages over IIR filters including:
◼ A completely constant group delay throughout the frequency
spectrum. Group delay refers to the time delay between when a signal
goes into the filter and when it comes out. Constant group delay
means that an input signal will come out of the filter with all parts
delayed by the same amount and with no distortion.
◼ Complete stability at all frequencies regardless of the size of the filter.
FIR filters also have some disadvantages:
◼ The frequency response is not as easily defined as it is with IIR filters
◼ The number of coefficients required to meet a frequency specification
may be far larger than that required for IIR filters.
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