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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <email@example.com> <_MgV9.firstname.lastname@example.org>
Subject: Re: Help analysing a CMOS ring oscillator
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 17 Jan 2003 08:40:36 -0000
NNTP-Posting-Date: Fri, 17 Jan 2003 08:40:41 GMT
Jeff Verive wrote:
>> The basic problem isn't. Its actually quite complicated. It took me
>> several pages of calculations to come up with a correct formula for a
>> simple 3 stage feedback ring where there was only a millor capacitor
>> and a gm included in the model. I'll see if I have time to post the
>> details on my site.
> Stop trying to model this as a linear AC amplifier. In a CMOS ring
> oscillator of several stages, each stage spends very little of its
> time in the active region.
False. I'll send you a working SuperSpice schematic of a 2.5Ghz vco if
you would like. The waveforms are resonable sinewaves.
>Instead, each stage should be modeled as
> two independent switches driving a small (albeit non-linear)
Nope. This shows you have little knowlede of 3 ring oscilators. Indeed,
you usually have to take its output to another gain stage to get a full
I agree that the best thing to do is to model this in
> SPICE and be done with it, but the OP didn't seem interested in doing
> so. Nonetheless, analyzing this as a succession of linear AC
> amplifiers is missing the point.
Not at all. That's how these oscillators work. They don't work as large
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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