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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Zero Crossing Circuit
Date: Sat, 02 Nov 2002 20:51:47 GMT
NNTP-Posting-Date: Sat, 02 Nov 2002 12:51:47 PST
john jardine wrote:
> "MUSTSEE ME" wrote in message news:...
> > Hi,
> > I am looking for a wideband zero-crossing detection circuit. I need to
> > detect zero crossing (both negative and positive crossing) of sine wave at
> > 100kHz-500kHz.
> > I have tried MAX907CPA, but the output is too noisy. Also, LM393 does not
> > give me a true zero crossing.
> > Does anyone have any suggestion?
> > Thank you
> > firstname.lastname@example.org
> 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 email@example.com
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