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NNTP-Posting-Date: Sat, 02 Nov 2002 20:20:48 -0600
From: "MUSTSEE ME"
References: <email@example.com> <3DC43B02.firstname.lastname@example.org>
Subject: Re: Zero Crossing Circuit
Date: Sat, 2 Nov 2002 21:26:29 -0500
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Thank you very much folks.
I will try as you all suggest !!!
"Chuck Simmons" wrote in message
> john jardine wrote:
> > "MUSTSEE ME" wrote in message
> > > Hi,
> > >
> > > I am looking for a wideband zero-crossing detection circuit. I need to
> > > detect zero crossing (both negative and positive crossing) of sine
> > > 100kHz-500kHz.
> > >
> > > I have tried MAX907CPA, but the output is too noisy. Also, LM393 does
> > > give me a true zero crossing.
> > >
> > > Does anyone have any suggestion?
> > >
> > > Thank you
> > >
> > > email@example.com
> > By 'noisy' I assume you mean you are detecting too many Xovers. This
> > would be due to noise on the incoming signal not normally visible
> > looking at the whole waveform but noticeable in the mV area by the
> > detector. You could CR filter the incoming sine wave but the timing
> > points will be delayed pro rata with the filter. Or ... the i/p signal
> > can be regenerated (frequency/phase) by a phase locked loop (#4046
> > say)sufficient to lose the Xover noise. You would then have a 'rate of
> > change of input frequency' loop tracking limit.
> I looked at this for wobble detection in CD and DVD. I have to have a
> PLL anyway but I found that it was useless to attempt to get zero
> crossing information from the PLL. Basically, I have to use the PLL to
> get a reference clock so that zero crossings can be "binned" to extract
> data instead. That means the raw sine wave still has to go to a zero
> crossing detector. We don't know the OPs application but if there is
> information in his raw "sine wave," he will have the problem that
> sidebands may be drastically suppressed by a PLL and the information
> possibly modified beyond recognition or entirely lost.
> ... The times have been,
> That, when the brains were out,
> the man would die. ... Macbeth
> Chuck Simmons firstname.lastname@example.org
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