[time-nuts] Nifty "MINI TIC" for DMTD work detail Info please read

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Nov 21 04:20:56 UTC 2012


The attached circuit is somewhat more efficient and a little quieter.
With a little elaboration lower distortion is possible.

Bruce

Bob Camp wrote:
> Hi
>
> Given that common practice is to mis-match the IF port on the mixers, it's probably not realistic to depend on exact match for isolation. Simple / cheap common base buffers likely are a better approach. Lots of isolation and not much flicker noise.
>
> Bob
>
> On Nov 20, 2012, at 9:01 PM, Bruce Griffiths<bruce.griffiths at xtra.co.nz>  wrote:
>
>    
>> The details about matching (if any) used in the Czech DMTD would be informative.
>>
>> To avoid degrading the performance of the DMTD system below that imposed by the mixers any isolation amps used will need a flicker phase noise floor below that of the mixers.
>> Even an opamp based isolation amplifier can be at least 10dB quieter (for offsets of 10Hz and below) than a typical minicircuits RF amp.
>> This is still about 10dB or so worse than a good mixer.
>> A well designed low gain isolation amp built with discrete transistors can have significantly lower additive phase noise than an opamp.
>>
>> To reduce the DMTD system noise one can either:
>>
>> 1) Carefully match all ports using series resistors, pads etc as necessary to achieve the required isolation together with a high output low flicker phase noise amplifier to drive the splitter
>>
>> 2) Use isolation amplifiers with very low flicker phase noise.
>>
>> Some isolation between the 2 RF inputs of a DMTD is usually necessary to avoid injection locking of the 2 sources being compared.
>>
>>
>> Bruce
>>
>> Bob Camp wrote:
>>      
>>> Hi
>>>
>>> Those isolation numbers are *highly* dependent on very good matching at all ports. That's rarely the case unless you have a bunch of pads running around the system.
>>>
>>> Bob
>>>
>>> On Nov 20, 2012, at 5:49 PM, Bruce Griffiths<bruce.griffiths at xtra.co.nz>   wrote:
>>>
>>>
>>>        
>>>> Typical Minicircuits SMT RF amps have a phase noise at best 20dB worse (@10Hz offset) than the mixer/phase detector.
>>>> Their reverse isolation is quite low (<<40dB)
>>>>
>>>> The principle reason that the Czech DMTD has such low internal noise is due to the absence of any isolation amplifiers.
>>>> They use the outputs of a 2 way splitter to drive the LO inputs of the mixers.
>>>>
>>>> A output to output isolation of 40dB or more at 10MHz is possible with some minicicuits splitters (e.g. SYPS-2-1).
>>>> The ZRPD1 has an RF1 - RF2 isolation of around 70dB at 10MHz.
>>>>
>>>> With a channel to channel isolation of around 110dB for a 2x ZRPD1 + Splitter combination isolation amplifiers may not be necessary.
>>>>
>>>> Bruce
>>>>
>>>> Bruce Griffiths wrote:
>>>>
>>>>          
>>>>> Since mixer noise is one of the limiting factors using a mixer with low flicker noise will help.
>>>>> NIST found that a custom mixer using diode connected (collector base short) 2N222As had a significantly lower flicker phase noise than either the ZRPD1 or the 10534A.
>>>>> They used off the shelf 1:5 impedance ratio transformers (probably from Minicircuits).
>>>>> Another issue is the flicker phase noise of any isolation amplifiers used.
>>>>> This is particularly critical if each mixer uses its own isolation amplifiers.
>>>>>
>>>>> My current amplifier phase noise measurement setup (for measuring the additive PN of a pair of well matched amplifiers) has a self noise of around -170dBc/Hz @ 1Hz offset for a 10MHz input.
>>>>> Ideally the additive phase noise of any isolation amplifiers should be well below that of the mixers.
>>>>>
>>>>> Bruce
>>>>>
>>>>> EWKehren at aol.com wrote:
>>>>>
>>>>>            
>>>>>> Yes Bruce I have the paper. I am not suggesting to copy it verbatim but if
>>>>>> there is a way to reach reasonable priced 1 E-14 members of the list should
>>>>>> pipe  in. I am willing to do an other board. the rest of the systems well
>>>>>> on its way.  Einally after three years.
>>>>>> Bert Kehren
>>>>>>
>>>>>>
>>>>>> In a message dated 11/20/2012 3:28:57 P.M. Eastern Standard Time,
>>>>>> bruce.griffiths at xtra.co.nz writes:
>>>>>>
>>>>>> EWKehren at aol.com wrote:
>>>>>>
>>>>>>              
>>>>>>> The D/M is being revisited  because  of the counter performance. 1 E-13 is
>>>>>>> easily attainable  but the Czech IREE  published a paper and claim 2 E-15.
>>>>>>>
>>>>>>>
>>>>>>>                
>>>>>> Do you mean the paper ""optimization of dual-mixer time-difference
>>>>>> multiplier" ?
>>>>>> The ZCD developed in this is a bit of a kludge and is far  from optimum.
>>>>>> Reverse engineering the circuit from the description given in  the paper
>>>>>> isn't too difficult.
>>>>>> They claim an instrument limited ADEV of  ~7E-15 @ 1s.
>>>>>> Do you have a copy of this paper?
>>>>>>
>>>>>>              
>>>>>>> Bert  Kehren   Miami
>>>>>>>   _______________________________________________
>>>>>>>
>>>>>>>
>>>>>>>                
>>>>>> Bruce
>>>>>>
>>>>>>
>>>>>>              
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>>>>          
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>>>        
>>
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>
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