[sdiy] mosfet/cmos opamp
harrybissell at wowway.com
Thu Oct 28 18:57:23 CEST 2010
Maybe the 10pA is over the temperature range ???
----- Original Message -----
From: Ian Fritz <ijfritz at comcast.net>
To: David G. Dixon <dixon at interchange.ubc.ca>, 'Harry Bissell' <harrybissell at wowway.com>
Cc: 'synth-diy DIY' <synth-diy at dropmix.xs4all.nl>
Sent: Thu, 28 Oct 2010 12:54:01 -0400 (EDT)
Subject: RE: [sdiy] mosfet/cmos opamp
At 10:21 AM 10/28/2010, David G. Dixon wrote:
>I typically use LF44x (IBC 10pA typ, 100pA max) for S&H buffers, and have
>been very pleased with the results. These have similar input current specs
>to CA3140 (IBC 10pA typ, 50pA max) and significantly better specs than TL07x
>(IBC 65pA typ, 200pA max), but really any of them will do for S&H unless you
>hold the sample for minutes.
Something I've never understood. Yes, it says 10 pA for the CA3140 (@ 15
V). But it also says 1.5 TOhm input impedance. What is the explanation for
this huge discrepancy? But whatever the spec sheet says, I measure under 2 pA.
Whether "any of them will do for S&H" depends on how large a cap you
use. You are using 100 nF. I am using 5 nF, in order to be able to charge
it in 30 usec. So I disagree with your conclusions by a factor of 20. :-)
Harry Bissell & Nora Abdullah 4eva
More information about the Synth-diy