[time-nuts] Isolation achieved by opamp based isoamp?

[Bruce Griffiths]

Stephan Sandenbergh wrote:
> Something that would be interesting to know is if certain opamps are better
> suited toward S12 isolation than others. I guess at the expense of noise
> floor and 1/f corner one could cascade two opamps to improve the S12
> isolation further.
>
>    
The flicker noise corner of an opamp may be lower than you think.
Current feedback opamps may have higher flicker noise corners than volt 
feedback opamps
> As soon as you are looking at frequencies of 100MHz you are probably left
> with the discrete options in any way.
>    
There are 1GHz and 10GHz opamps available.

Bruce
>
> On 22 November 2013 11:45, Stephan Sandenbergh<ssandenbergh at gmail.com>wrote:
>
>    
>> Thanks for the spec. I suspected that it would be in that ball park.
>>
>> The discrete transistor type amplifiers achieve around 120dB or more at
>> 10MHz. But, they are a lot more effort to implement than the opamp designs.
>>
>> I believe the transformer in this case is for ground loop isolation rather
>> than S12 isolation.
>>
>>
>> On 21 November 2013 20:20, Charles Steinmetz<csteinmetz at yandex.com>wrote:
>>
>>      
>>> Corby wrote:
>>>
>>>   This opamp buffer has 80-90db isolation.
>>>        
>>>>          
>>> That is typical at 5 to 10 MHz *if* (i) all of the splitting is done on
>>> the input side (i.e., each output has its own op amp), and (ii) the
>>> splitter and all of the construction (grounds, shielding, etc.) is done
>>> correctly.
>>>
>>> If any splitting is done on the output side of the op amp(s), by using
>>> one op amp to drive more than one output through separate back terminating
>>> resistors, the outputs that share an op amp will only be isolated by 30 to
>>> maybe 40 dB (again, assuming that the op amp has been well chosen and all
>>> of the construction is done correctly).
>>>
>>> Best regards,
>>>
>>> Charles
>>>
>>>
>>>
>>>
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>>
>>      
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