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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: Sat, 18 Jan 2003 07:59:44 -0000
NNTP-Posting-Date: Sat, 18 Jan 2003 07:59:49 GMT
Jeff Verive wrote:
> "Kevin Aylward" wrote in message
>> 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.
> I'll bet his CMOS ring oscillator is not running over 100 MHz. Mostly
No chance. Hint. I know how to run simulations with BSim3 models.
>>> 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 rail swing.
> Obviously, you've never built one of these.
I build them all the time in SuperSpice:-)
> oscillators, they spend a lot of time at the rails. Very little time
> as linear amps.
Not on your nelly. They not relaxation oscilators. Its that simple. You
dont know what your talking about.
>He stated nothing of feedback to buy the extra gain,
> which is usually not necessary in a 3-ring relaxation oscillator.
I've emailed you a basic 3 stage cmos ring SuperSpice schematic. Please
adjust the values and make it act as a relaxation oscillator. Oh, and as
it stands oscilates at around 4Mhz, not Ghz.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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