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

[Stephan Sandenbergh]

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.

As soon as you are looking at frequencies of 100MHz you are probably left
with the discrete options in any way.


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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>
>