[time-nuts] DMTD using Active Mixers

[Bob Camp]

HI

I have no direct experience with the Minicircuits "active mixers", but  
I have used some of their amplifier chips. I suspect they use their  
own amps.

The amps I worked with had significant phase noise issues when driven  
within 6db of their 1db compression point.  They were "ok" at low  
drive levels. More or less then went from 3 db noise figure to a > 20  
db nf as you went from -20 dbm to  0 dbm output on a +7 dbm amplifier.

Bob

On Nov 11, 2009, at 7:39 PM, Magnus Danielson wrote:

> Bruce Griffiths wrote:
>> 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.
>
> While it confuses matters, it is usefull to know about them, since  
> they may be good for some designs, but maybe not for DMTD designs.
>
> I have argued that keeping a buffer-amplifiers (not to be confused  
> with the -120 dB isolational amp) just at the mixer will relief the  
> issues of VSWR to tempco. Also, getting that extra boost is also  
> good. Needs to have meaningfull phasenoise to be usefull thought.
>
>> Whereas I was referring to mixers like gilbert cell mixers as  
>> active mixers.
>
> I was making the same distinction. Passive JFET mixers is just  
> another variant to using schottkydiodes.
>
>> With the Minicircuits so called active mixers one needs to measure  
>> their  phase noise in order to make meaningful comparisons.
>
> Indeed. Their target is probably not considering cutting edge DMTD  
> systems.
>
> Cheers,
> Magnus
>
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