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From: "Peter Nolan"
References: <5Q1H9.32847$zX3.firstname.lastname@example.org> <3DEE2C3D.A5902908@rica.net> <3DEE23DC.email@example.com> <3DEF8612.firstname.lastname@example.org>
Subject: Re: 100Hz from 25.6kHz crystal.
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Fri, 6 Dec 2002 12:21:32 -0000
NNTP-Posting-Date: Fri, 06 Dec 2002 12:21:00 GMT
My Vdd is 9V.
To email please remove x from email@example.com
"Fred Bloggs" wrote in message
> Gary Richardson wrote:
> > "Fred Bloggs" wrote in message
> > news:3DEE23DC.firstname.lastname@example.org...
> >>Peter Nolan wrote:
> >>>The circuit now works with the following values:
> >>>Rbias=4.7MOhms and R2=750kOhms.
> >>>C2=100pF and C3(the trimmer) around 30pF.
> >>>Many thanks.
> >>>Peter Nolan.
> >>>To email please remove x from email@example.com
> >>The 750K will result in quite a bit of added phase noise beyond a more
> >>sensible value. The original configuration was not working because you
> >>were exciting a parasitic mode or maybe power pin feedback. Go for 60
> >>degree phase shift across R2-C2 at the operating frequency. You want to
> >>use a temperature stable C2 so maybe 1000p in C0G is convenient. Then
> >>you have TAN(60)=2 x pi x 25.6K x R2 x 1000p which solves for R2=10-12K
> >>for an RMS Johnson reduction of nearly 40dB per root-Hz due to that
> > The max drive level of the C-2 type xtal is 1uW. Will an R2 of 10-12K
> > satisfy that requirement?
> Ahhh- good point, Gary. This will depend upon his Vdd. I will run it
> through the sim and see what the limits are....
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