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Subject: Re: incredible comparator behaviour
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
NNTP-Posting-Date: Wed, 08 Jan 2003 21:29:38 EST
Organization: Prodigy Internet http://www.prodigy.com
Date: Thu, 09 Jan 2003 02:29:38 GMT
"Martin" wrote in message
> Good Morning,
> I try use a MAX942 comparator. this is a dual fast comparator with
> Normally a simple to use device.
> But I encounter strange problems.
> I want to detect (at IN- pin) pulses of 1.2V High and about 100ns wide
> time about 15-20ns).
> But when I fix a threshold of 1.4V at IN+, the device is switching and I
> have a pulse at the output.
> The height of the pulse is decreasing when I rise the threshold.
> I need to rise the threshold at 3V to avoid the pulse at the output.
> (the scope used to see the signals is 500MHz bandwidth)
> (power supply is 5V, threshold perfectly stable)
> (I tried several chips)
> Can anyone help me on this incredible behaviour?
> Thank you very much.
Without knowing more, it sounds like the device might be oscillating.
Strange behavior in comparators is often due to unseen oscillation or
instability. Be sure the device is bypassed properly and that leads are
short, etc. Also, be sure the driving and threshold impedances are low.
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