[time-nuts] Phase Detectors/Mixers for DMTD and PN measurements

[Joseph Gwinn]

On Wed, 11 Dec 2019 12:00:02 -0500, time-nuts-request at lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 185, Issue 17
> ------------------------------
> 
> Message: 4
> Date: Wed, 11 Dec 2019 23:36:29 +1300 (NZDT)
> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at lists.febo.com>
> Subject: Re: [time-nuts] Phase Detectors/Mixers for DMTD and PN
> 	measurements
> Message-ID: <1772914487.1926367.1576060590010 at webmail.xtra.co.nz>
> Content-Type: text/plain; charset=UTF-8
> 
> There are a number of NIST papers on this:
> https://tf.nist.gov/general/publications.htm
> 
> You can also simulate the effect of a capacitive IF port load.
> However a capacitive load can also degrade the isolation and RF and 
> LO port mismatch.
> 
> One can also use diode connected BJTs instead if lower close in PN is 
> desired at least for frequencies up to 10MHz or so.
> There is a NIST paper on this as well:
> https://tf.nist.gov/general/pdf/2556.pdf
> 
> Bruce

I recall that Enrico Rubiola wrote a paper on the care and feeding of 
diode-ring mixers.  It will be on Enrico's rubiola.org website.

Joe Gwinn



>> On 11 December 2019 at 22:55 Tobias Pluess <tobias.pluess at xwmail.ch> wrote:
>> 
>> 
>> Hi colleagues
>> 
>> In parallel to my GPSDO project I am also thinking about a DMTD 
>> measurement system which should also be capable of doing phase noise 
>> measurements. This will be necessary to measure the stability and 
>> phase noise of my own GPSDO.
>> 
>> There is the paper from W. J. Riley, "A small DMTD system". He uses 
>> TUF-R3SM+ mixers. The HP 11729C carrier noise test set uses a custom 
>> HP part as phase detector, and a lot of other publications I found 
>> use the HP 10514A, either as mixer or as phase detector.
>> I wonder, which criteria are relevant to select a mixer for this 
>> application (besides the frequency range). Are there devices which 
>> are better when used as mixers, or phase detectors, or are there 
>> even devices which are good for both purposes? Of course, we want 
>> low noise, but for most if not all commercial mixers, only the 
>> isolation and conversion loss is specified, but I never saw a mixer 
>> datasheet having information about the mixer's noise contribution. 
>> So there must be other criteria people use when selecting a mixer 
>> for a DMTD or phase noise measurement system.
>> 
>> Further. in this paper "OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE 
>> MULTIPLIER" from Sojdr I even found a reference "The mixer output 
>> has a capacitive loading (22 nF) that increases the zero-crossing 
>> slope". The "Small DMTD system" from Riley also does have this 
>> capacitive loading. Can somebody explain why this does help to 
>> improve the zero crossing slope?
> 
> End of time-nuts Digest, Vol 185, Issue 17
> ******************************************