[time-nuts] pulling oscillators

[lists at lazygranch.com]

A crystal is a high Q circuit. You can't pull them much. I think your first idea about yanking the crystal and just driving the pin is a better idea.

If the part has a shutdown feature, it would pay to determine the state of the crystal input pins when in the shutdown mode. 

 
-----Original Message-----
From: "Don Latham" <djl at montana.com>
Sender: time-nuts-bounces at febo.com
Date: Sat, 5 Mar 2011 02:06:18 
To: time nuts<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] pulling oscillators

Hello all:
I've developed a need for pulling crystal oscillators built in to pll
circuits. These are cmos, and have the common style oscillator circuit
built in. The crystal is across an inverter in the chip, and there is a
small cap between each end of the crystal and ground.
The chips are pll's in radio transceivers, early at that.
I could carefully remove the crystals and caps, simply driving the
non-inverting input on the chip with the reference, but I would rather
simply tack on a very small cap and "pull" the crystal oscillator with an
external reference signal of the right frequency.
Anyone out there tried this?
Thanks
Don



-- 
"Neither the voice of authority nor the weight of reason and argument are
as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com


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