[time-nuts] DMTD using Active Mixers

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Nov 11 22:30:12 UTC 2009


Magnus Danielson wrote:
> Bruce Griffiths wrote:
>> Magnus Danielson wrote:
>>> Bruce Griffiths wrote:
>>>> Active mixers almost invariably have a higher noise floor than 
>>>> passive mixers, particularly in the flicker noise region.
>>>> Consequently a DMTD system using active mixers will have a higher 
>>>> system noise floor than one using active mixers.
>>>
>>> ... than one using passive mixers.
>>>
>>> You still need driving amplifiers.
>>>
>>> Cheers,
>>> Magnus
>>>
>> Its much easier to ensure that the flicker phase noise of a buffer 
>> amplifier is low than it is to achieve a low flicker phase noise for 
>> an mixer using nonlinear active devices.
>> Even passive FET mixers have higher flicker noise than passive mixers 
>> using schottky diodes.
>
> True, but my comment was rather to say that it will most probably not 
> be all passive, but I completely agree (as you very well know) that 
> phase noise of amplifiers is much better contained than that of mixers.
>
> Cheers,
> Magnus
>
Hej Magnus

To confuse matters Minicircuits use the term active mixer for a 
conventional diode mixer that uses amplifiers on the LO and/or RF ports 
to boost signal levels.
Whereas I was referring to mixers like gilbert cell mixers as active mixers.

With the Minicircuits so called active mixers one needs to measure 
their  phase noise in order to make meaningful comparisons.

Bruce

Bruce





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