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Comments on How building a follower satisfying rather extreme requirements.

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How building a follower satisfying rather extreme requirements.

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What is your best suggestion for building a follower that would ideally satisfy the following spec:

  • frequency: from 100 Hz (or lower) to 1 GHz
  • input signal impedance: 1 Mohm
  • input signal amplitude: from 1 mV to 1V at least
  • output load to be driven: 50 Ohm.
  • The follower need not be absolutely flat (gain = 1), but actually, it is allowed to reduce the signal by a factor of 0.5.
  • some signal distortion allowed.
  • also, a small DC offset voltage of few mV can be allowed, as I am interested in the AC component of the signal.

If that is not possible, please give me the suggestion that best approaches these specs. Also, I would be happy if the part names or part numbers are indicated.

EDIT: as pinpointed by Olin Lathrop, the 1 GHz requirement is fundamentally incompatible with the 1 M Ohm input impedance requirement. So, there is no point to go further for the moment.

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General comments (5 comments)
General comments
Andy aka‭ wrote over 3 years ago

Have you tried looking for wide bandwidth unity gain stable op-amps?

coquelicot‭ wrote over 3 years ago

Not with those keywords. Will try and perhaps delete this question.

coquelicot‭ wrote over 3 years ago · edited over 3 years ago

For the moment, I've found the opa695 that is best suited, but it has 70uA input current. Also, the big 50 Ohm load is a problem.

Lundin‭ wrote over 3 years ago

This is far from my area of expertise, but have you checked Analog Devices? They have tonnes of more or less exotic amplifiers. https://www.analog.com/en/products/rf-microwave/rf-amplifiers.html. If you for example check their "Wideband Distributed Amplifiers" they have lots of parts explicitly designed for 50 ohm, mostly with matched input/output.

coquelicot‭ wrote over 3 years ago

@Lundin. Thank you for the link. I will have a look.