Transfer Function Derivation
Digital filters are often described and implemented in terms of the difference equation that defines how the output signal is related to the input signal:
where:
- is the feedforward filter order
- are the feedforward filter coefficients
- is the feedback filter order
- are the feedback filter coefficients
- is the input signal
- is the output signal.
A more condensed form of the difference equation is:
which, when rearranged, becomes:
To find the transfer function of the filter, we first take the Z-transform of each side of the above equation, where we use the time-shift property to obtain:
We define the transfer function to be:
Considering that in most IIR filter designs coefficient is 1, the IIR filter transfer function takes the more traditional form:
Read more about this topic: Infinite Impulse Response
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