[time-nuts] DMTD - analog multiplier vs. diode mixer ?

Bob Camp kb8tq at n1k.org
Thu Jan 7 18:11:14 EST 2016


Hi

If your intention is to run a mixer with saturated inputs …. just run
an X-OR gate. It will handle the high level signals much better than
an over-driven analog part. 

Yes *somebody* should check out a board built that way …. I’ll
let you know when I do. 

Bob


> On Jan 7, 2016, at 7:35 AM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Wed, 6 Jan 2016 18:30:07 -0800
> "Richard (Rick) Karlquist" <richard at karlquist.com> wrote:
> 
>> Read Gilbert's paper or Gray and Meyers analog IC textbook and
>> you will see that the whole theory of operation of these
>> depends on keeping the signal levels in them very small,
>> especially if linearity (actually translinearity) is
>> important.  They always have current sources in the
>> emitters that contribute a lot of noise.  So you have
>> small signals and large noise.  The IC's that are
>> designed to be DC coupled have even more sources of
>> extra noise.
> 
> How about using the Gilbert Cell as "digital" mixer,
> ie driving the currents hard from one branch to the other
> and replacing the current sources by resistors?
> 
> How much would that improve the noise? Would it be still much
> worse than the diode mixer?
> 
> 			Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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