Use of Diodes in Filters??

[Rob Hukin]

>	>Maybe i'm missing something here, but isn't there a
>relationship between
>	>the number of diodes in the ladder and filter order? So, in the
>EMS filter,
>	>diodes D3, 4, 5, 10, 11 and 12 maybe to do with matching/better
>SNR, but
>	>the rest and required to get a 4-th order response?
>
>Unfortunately, no.
>You can get the number of poles (or the order) by counting the
>(relevant) *capacitors*.

Of course - I should've been more explicit. What I meant to say was that
(in the EMS example), it's the combination of the other diodes (6, 7, 8, 9,
13, 14, 15 and 16) *and* the capacitors that give you the frequency
response. It was just that the previous messages in this thread (in which
the original poster was asking about multiple diodes in filters) seem to
miss out this rather important point.

>Example VCS-3 diode ladder:
>(1) Number of caps in the ladder = 4, i.e. 4-pole filter.

4 caps + 8 diodes = 4-pole filter.

>(2)Location of these poles determined by unbuffered structure, and by
>using
>several diodes in series for the last (upper) stage results in a
>response that
>is more like 18dB/Oct than the 24dB you'd expect from a 4-pole filter.

Why is that?

I don't remember ever seeing diode ladder filters other than 4-pole. Do
they exist?

rob.