Descret OTA was "that Japanese site"

[terry michaels]

Message text written by Joachim Verghese
>terry michaels wrote:

> I looked through my files and I couldn't find the ARP filter module you
are
> referring to.  Maybe you can e-mail me the module number.

I think Juergen referred to the 4023 filter. The integrators are
LM301 with a FET buffer in front. The gate (which is at a constant
potential) of the FET is decoupled to ground by means of a 1 nF
cap for RF stability, I gather -- the LM301 obviously isn't terribly
fast.

I think the 4023 is still downloadable in PS format from my "website".

http://www.netcontrol.fi/~jocke/arptech/submod/4023/

cheers,

-joachim

<
Hi Joachim:

You are correct in pointing out the gate is at a constant potential, which
would seem to indicate the 1 NF capacitor would only have an effect at
frequencies high enough that the open loop gain of the op-amp is
approaching unity.   I don't have the means to model the circuit to confirm
this.   It seems like a very large value for noise gain concerns or RF
stability, so I'm not sure if that is its purpose. The 100 PF cap is the
integration cap.

The LM 301 is faster than you think in this circuit, it is de-compensated
by using a 3.3 PF cap.  That will produce a speed increase of 9 times.

Terry Michaels