How are the IC's calculated in the IIR Cascade Filter with I.C. vi

[TroyR]

How are the IC's calculated in the IIR Cascade Filter with I.C. vi

[JuanCarlos]

Hi,

The VI "IIR Cascade Filter with I.C." actually let's you pass to the filter the initial condition of the filter's circular buffer. This feature will help you pass any initial data for the buffer.

The use of the initial condition is reserved for cases where you are performing a filter and you want to specify an initial condition to avoid the settling time involved in a digital filter.

In general if the order of the filter is not very high and the data buffer is long enough you don't need the initial condition; probably using the "IIR Cascade Filter" will do it.

Hope this helps.

Regards,

Juan Carlos
N.I.

[TroyR]

Thanks for the reply Juan,
However I am looking for the equations.
My application calls for a 'speedup' of the transient resposne, I realize I could just artificially load the filter, however I would like to take a look at the equations.
Regards
Troy Richards

[TroyR]

Solved this myself.
See attached VI.

[TroyR]

Solved this myself.
Attached llb has subVI that computes the IC's needed to remove transient given a constant value step input to the IIR Filter.
Computes filter state (see app note 39) for cascade filter using z-transform final value theorem.
This version works for all filter types, ie lowpass, highpass, bandstop and bandpass.