[sdiy] variable width pulse wave for JEFT sample and hold

[David G. Dixon]

Dan,

Why not just use an RC high-pass filter with a time constant of about 10 us
to generate spikes from the square (0.001 uF and 10 k will do nicely), and
then shift the pulses with a unity-gain inverting opamp with a voltage 2:1
divider off the positive input between -15V and 0V so that the output DC
rides at about -5V and the spikes go up to 0V to trigger the JFET (which, I
presume, is npn and therefore is full off at about -3.5V and full on at
about 0V)?


David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C.  V6T 1Z4
Canada
 
Tel 1-604-822-3679
Fax 1-604-822-3619
 
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-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dan Snazelle
Sent: Tuesday, January 06, 2009 9:14 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] variable width pulse wave for JEFT sample and hold


i am trying to find a way to get a variable pulse wave from a square so that
i can successfully clock a sample and hold built around a JFET (pn4391)

i am having no luck with a regular square wave.

thanks






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