sg531p clock oscillator IC ... output is ringing

Dec 22, 2005 3 Replies

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samIam 20 years ago

I am using a 3.68Mhz sg531p in a hobby project I am working with. Long story short, I plan to feed it into a PAL and divide it down to the frequencies I need to drive a microprocessor based project.

This morning after failing to track down why the circuits are switching erratically I conncected a scope to the output of the sg531p. I see ringing ... overshoots and undershoots as well.

Any advice on how I can get rid of this? I need a ttl level output to drive my circuit ... and have invested in a bunch of sg531p's I would like to put to use.

Thanks

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Tim Wescott 20 years ago

You are seeing reflections on your clock line.

Web search on "clock", "termination" and "reflection".

If you're using a PC board the answer is probably a series termination resistor right at the clock output pin. If you're using a proto board then you should either consider running the clock through an RC low-pass filter with a time constant of around 25ns or you should consider distributing your clock with a twisted pair (clock and ground) and the series termination mentioned earlier.

Tim Wescott Wescott Design Services http://www.wescottdesign.com

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samIam 20 years ago

The circuit is on a large solderless breadboard. I am going to google your suggestions.

Thanks Tim.

Tim Wescott wrote:

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Joerg 20 years ago

Hallo Sam,

If it's the white board you stick parts into those aren't always very suitable for fast digital stuff. While your circuit might be intended to generate 3.68MHz the chip itself is probably a whole lot faster. Thus it can create very fast spikes on its outputs and also on its supply rails.

I'd build it up on a board that has a full ground plane. Either one of those Eurocards or do the 'living bug' thing on copper clad.

Regards, Joerg

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