[time-nuts] DMTD downmixer question

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jul 1 07:15:03 EDT 2016

The optimum sine to square converter is embodied in the Collins style limiter approach consisting of a cascade of limiting amplifiers each with suitable individual gain and individual bandwidth, the gain and bandwidth increasing for each successive stage until the output slew rate is sufficient to drive a comparator without the comparator contributing significant additional jitter.
 Other approaches invariably produce greater output jitter.details here:
Bruce's: Zero Crossing Detectors - KO4BB

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      From: Stéphane Rey <steph.rey at wanadoo.fr>
 To: 'Discussion of precise time and frequency measurement' <time-nuts at febo..com> 
 Sent: Friday, 1 July 2016 8:45 PM
 Subject: [time-nuts] DMTD downmixer question
Hi there,

I will receive my SR620 soon and want of course to use it as well for 
stability measurement using the DMTD method.

I've read many things on how to design the downmixer. There will be a 
DDS or low noise generator as LO, the two mixers, and the squarer. There 
are apparently many ways to do the squarer. Some of the ways I've seen 
are using fast comparator, logic gate, fast amplifiers...
Finally is there a way which looks better than the others ? I was 
hesitating between a fast comparator and an ECL logic gate for instance.

Thanks & cheers

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