From: Jim Thompson
Subject: Re: Help analysing a CMOS ring oscillator
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Date: Tue, 14 Jan 2003 15:38:47 GMT
NNTP-Posting-Date: Tue, 14 Jan 2003 10:38:47 EST
Organization: Cox Communications
On Tue, 14 Jan 2003 08:22:08 -0000,
"Kevin Aylward" ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: Help analysing a CMOS ring oscillator",
Wrote the following:
|Jeff Verive wrote:
|> "Kevin Aylward" wrote in message
|>> Nope. DC gain is not relevant at all. The oscillator will oscillate
|>> when the gain is around 1. This is way off from the DC gain. The HF
|>> gain is gm.Xc, where Xc is the effective capacitance load.
|> Gee, and where does that AC gain come from? Yes, you can oscillate
|> with unity gain, but the fact is that an inverter stage can be
|> analyzed first as a DC circuit (even Spice uses successive DC
|> operating point interactions to determine AC gain).
|Indeed. You need to be able to set up its bias point in order to
|calculate things such as gm, however, this is not relevant to the point
|that DC gain itself is not important in calculating the main
|characteristics of an oscillator. One can have a Dc gain of 20db, 40db,
|60db, etc, without it effecting the oscillating frequency at all. That
|is there is no direct relation to oscillation and dc gain at all.
Kevin must still be on the suds ;-) What he's saying, but can't put
his finger on the succinct word, is that it's GAIN-BANDWIDTH that
matters, NOT DC GAIN.
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
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