From: "George R. Gonzalez"
Subject: Re: incredible comparator behaviour
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
NNTP-Posting-Date: Thu, 09 Jan 2003 15:18:48 GMT
Organization: AT&T Broadband
Date: Thu, 09 Jan 2003 15:18:48 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.
You didnt mention important details, like are there several bypass
to the IC, are you using a ground plane, are you doing this on a EZ plug-in
With rise times that fast, all it takes is a few nanohenries or picofarads
to add ringing to the inputs
or ground or Vcc rails, enough ringing to mess things up.
The easiest way to debug this is to start applying 0.01uf capacitors to the
ground-vcc rails and
see if that changes anything. Also try applying 10 to 1000pf capacitors to
the inputs and see if that changes anything.
You may need some series resistors on the inputs to damp ringing too.