AW: Use of Diodes in Filters??
Juergen.Haible at nbgm.siemens.de
Thu Nov 20 17:43:32 CET 1997
>Maybe i'm missing something here, but isn't there a
>the number of diodes in the ladder and filter order? So, in the
>diodes D3, 4, 5, 10, 11 and 12 maybe to do with matching/better
>the rest and required to get a 4-th order response?
You can get the number of poles (or the order) by counting the
(relevant) *capacitors*. (Now, even *this* is not generally true,
as caps might be splint in two for some reason, and you have to
be careful to decide which coupling capacitor has an effect
in the relevant frequency range, and which not. Not to speak
of bypass caps of course)
Number of diodes is not relevant for the number of poles, as they are
only used as variable resistors.
Number of diodes in series at a certain part of the circuit is important
for the *location* of poles, however. As is buffering-or-not between the
Example VCS-3 diode ladder:
(1) Number of caps in the ladder = 4, i.e. 4-pole filter.
(2)Location of these poles determined by unbuffered structure, and by
several diodes in series for the last (upper) stage results in a
is more like 18dB/Oct than the 24dB you'd expect from a 4-pole filter.
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