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

Dan Snazelle subjectivity at hotmail.com
Thu Jan 8 20:25:37 CET 2009

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This statement brings up an issue i still am trying to learn..
how to level shift signals and voltages
(or voltage shift or offset)

it seems you are saying to do something like this:

input the square wave into a 102 cap with a 10k resistor to grnd. then the level shift: plug the signal into the inverting
input of an opamp, which on the non inverting input has a voltage divider ( 2 to 1 would that mean a 100k to + and 50k to gnd?

i would LOVE to be able to figure out this SHIFTING thing.

does anyone know of a chapter in any of the common opamp books that talks about it? is it technically called voltage shifting? or voltage offset?

thanks

I keep on learning new junk everyday
> 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
>
>
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> Vancouver, B.C.  V6T 1Z4
>
> 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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