[time-nuts] PN measurement of SSINE to CMOS converters

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Oct 27 05:22:07 EDT 2015


One of the attached circuits should be suitable to allow most sine to CMOS converter outputs to drive a 50 ohm load. The first, in particular, suits a modified Wenzel style circuit if one removes the 50 ohm resistor and connects the transformer primary, with the capacitor in series, directly across the 200 ohm collector load. 


     On Monday, 26 October 2015 5:04 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
   

 The technique I used to measure the PN contribution of the LTC6957-4 at 
10Mhz
Low noise 10MHz sinewave OCXO (Trimble 37265 removed from Thunderbolt 
(Thunderbolt has rather noisy output amplifier)). OCXO PN measured 
against a pair of similar OCXOs via correlation using the TimepodConnected 
to low noise RF amplifier (push-pull transformer feedback CB Norton 
amplifier NF ~ 2dB Z10043 from Clifton Laboratories) with a gain of 
~12dB.Output (~19dBm) from amplifier is split by a minicircuits 1:2 splitter 
(Minicircuits ZFSC-2-4)3dB 50 ohm passive attenuator reduces one output 
to ~ 14dBm this is connected to the Timepod reference input.
The other output from the splitter is attenuated with a passive 50 ohm 
attenuator to the desired input signal level for the DUT.
The DUT output drives a minicircuits 1:2 splitter via a lowpass filter.Each of 
the splitter outputs is connected to either Timepod Ch0 or CH2 via an RF 
amp (in my case a HELA10-D) with a gain of around 10dB.
Cross correlation ensures that the relatively high noise of the HELA10-D's 
isn't too significant, the trade off being that more time is required to 
average down their contribution to the measured noise.
I use an RF power meter to measure the output of each HELA10-Dto 
ensure that the Timepod input signal doesn't exceed the maximum rated 
input for the Timepod.
Alternatively if one has a sufficiently low noise amp like the Q-bit QB188 (NF 
~3dB Gain ~ 15 dB) a single amp connected directly to the Timepod signal 
input via a passive attenuator should suffice.
For most useful comparators or CMOS gates an ouput circuit like that on 
the LTC6957-4 evaluation board should suffice.

Bruce
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