[time-nuts] DMTD using Active Mixers

[Bruce Griffiths]

Mario

No there is no diode mixer in the AD831,  it uses a conventional Gilbert 
cell mixer with preceding LO and RF amplifiers.
Compared to a diode mixer it has high flicker noise and poor dc stability.

Bruce

Mario Sanchez wrote:
> Thanks for your inputs...
>
> I dont know exactly which are the microcircuits ActiveMixers you refer to;
> just to make it clear, the IC that I am using is Analog Devices AD831, which
> basically has a conventional diode mixer, a limiter amplifier in the LO
> input and a low noise output amplifier.
>
> Regards,
> Mario
>
>
> On Thu, Nov 12, 2009 at 1:39 AM, Magnus Danielson<
> magnus at rubidium.dyndns.org>  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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