I don't want to derail the other thread, but it sounds worthy of discussion, so here:
Are you sure you get a flat bandwidth up to 700MHz out of that module?
This is what it looks like after debugging:
https://www.seventransistorlabs.com/Images/WidebandAmpDebugged.jpg(bottom left of the scratch paper is relevant, for once)
Full schematic:
https://www.seventransistorlabs.com/Images/WidebandAmpSchem.pngInductors with "xxxR" are resistors of that value, and likewise for resistors in nH. Components shown with a resistance have that added in series (except for L6, that's just the DCR of the real component, a Coilcraft 1812CS part).
This version has lots of ESR added to dampen things. I made another more radical variant that's studded with more bypass caps, so I'd mixed up my descriptions there a bit.
Frequency response was measured with a not-very-flat noise source, and measuring the difference of averaged spectra. While the spectrum isn't very flat, I have no particular reason to doubt the gain is more or less correct: it's not in compression, or below the noise floor.
It scares the bejeezus out of me. Have you ever looked into it with a VNA? I know you have cured the instability but I'd expect to see spikes of negative resistance up above 2GHz from what I see in the version on screen.
Could be. I only have the spec (1.5GHz, but it actually stops at 1.8 or 2), and no signal generator or return loss bridge to work in that range.
Even if you grounded the base really well the BFR92 itself has parasitics and the output signal path looks quite long before it reaches the next BJT stage. There isn't much ESR here and I'm not sure what the input Z of the next stage is at 2GHz but there's enough trace length to do a decent trip around a smith chart at UHF so I'd expect to see negative resistance at the board input 'somewhere' in the upper UHF region and maybe beyond this. But I can only look and guess. I think other engineers at my place of work would also be scared of that module in a review
Good thing it's just for sitting on my bench and (hopefully) amplifying signals in the given range without trouble. Well, apparently not much trouble, in the range that I can see...
But even in those days I don't think a wideband (UHF) MMIC alternative would have been tolerated in a design review because of the risk of instability up at many, many GHz. i.e. at frequencies beyond the manufacturer's s parameter tables. There's nothing like putting a lid over a marginal amplifier design and then cooling it to -40degC to make it wake it up into oscillation
The other amp to which I referred (just now in the thread) is this,
https://www.seventransistorlabs.com/Images/20MHz_LNA.jpghttps://www.seventransistorlabs.com/Images/20MHz_LNA_Simpl.png (simplified, missing some impedance and frequency equalizing components)
It's around 3.2nV/rtHz in a 20MHz BW, which is obviously not very low at all, and nowhere near as low as the puny BFR92 is doing. It could be PBSS303NX is just not low noise (but it's a comparable device to the ZTX751, also unspecified for noise but happens to be good), but it seems more likely I've forgotten something gross about the circuit.
Red herring: the mirror bias network isn't it. I can replace it with a 150R resistor (base to GND) and get the same noise...
Tim