The four lines of parameters are both shared and particular and they are arranged as follows:
Value Analog/IIR/FIR shared
Value2 Analog/IIR/FIR shared
SpiceLine2 gain, attenuations and order
There are also hidden parameters, which are not in the symbol's list to avoid cluttering and because, as they are, they shouldn't need any modification (with their default values), but they can affect the results so they can (and should) be changed if needed.
No filter uses all the parameters which means that the unused ones can be safely ignored. For example (and keeping the default values) a Butterworth filter only needs the parameters marked in bold:
Value sigma=0.5 nT=0 Zin=1 Zout=1
Value2 Win=1 Choice=1 sim=1 test=0 SH=1 Fact=1
SpiceLine f0=2k fc=250 Bwp=100 BWs=200
SpiceLine2 G=1 Asc=3 Ap=1 As=40 N=13
f0 means its value won't affect the results. Neither will deleting the rest of the parameters, but that is not recommended.
In general, there are two methods of starting the configuration:
- letting the order be internally determined (
N=0) ⇒ all the pass-band and stop-band frequencies (
fc, BWp, BWs) and attenuations (
Asc, Ap, As) − case specific − are needed, or
- specifying the order (
N>0) ⇒ only the pass-band frequencies (
fc, BWp) and attenuations (
Asc, Ap − case specific) need to be set, the stop-band frequency (
BWs) will be internally determined while the stop-band attenuation (
As) will either be internally calculated or not be needed − case specific.
Using the same Butterworth example from above, this is how the values would look like for the two cases:
- All three frequencies are specified and their attenuations:
SpiceLine fc=250 Bwp=100 BWs=200
SpiceLine2 G=1 Asc=3 As=40 N=0
- The stop-band frequency is set to be greater than the pass-band, only; the stop-band attenuation has a "don't care" value.
SpiceLine fc=250 Bwp=100 BWs>BWp
SpiceLine2 G=1 Asc=3 As=x N=7
When the examples for each filter are given, the descriptions will list these two methods as a simple ennumeration. The exceptions to the rules will be explained later.
©Vlad, 2008 - 2015