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Old 22nd Oct 2018, 5:04 pm   #18
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 1,961
Default Re: 0.1-2000 MHz Wide Band Amplifier ~4

It depends on what is inside the MMIC and how much gain it has (up in the >GHz region) and what package it uses...

In this case I think there will be a two stage MMIC that gives 30dB gain at 1GHz and it uses a classic old SOT86 package. Normally, the SOT86 package is fine for most of the basic MMIC amps or 'modamps' in the MSA/MAR/ERA range. This is because there is usually a single stage amp with a pair of BJTs in a darlington config.

You still have to use several via holes close to the device ground legs with these classic MMICs but they are fairly forgiving unless you only fit a couple of vias on a thick PCB and space the vias a few mm away from the device legs. But it might take 0.5nH of via inductance to begin to see obvious problems.

However, if you have a two stage amp sharing the same SOT 86 SMD package and you have 30dB gain at 1GHz then the grounding requirements for the SOT86 package become much, MUCH more demanding. You could be looking at a net <0.05nH ground inductance requirement for the PCB vias in order to maintain good stability margins. It's a huge change in requirements for the PCB layout compared to a classic MSA/MAR/ERA MMIC from Avago or Minicircuits
Regards, Jeremy G0HZU
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