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The bi-polar transistor at RF

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July 22nd 04, 06:46 PM

Paul Keinanen

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On Thu, 22 Jul 2004 16:01:02 +0000 (UTC), (John S.
Dyson) wrote:

"Noiseless feedback' is very helpful to mitigate the excess amounts
of gain, while pushing the return loss match (the impedance match)
closer to the noise match (the input impedance where the noise is lowest.)
A simple emitter (source) inductor and a little bit of parallel, noisy
feedback can be used to tame some of the interesting UHF+ components.
(The emitter (source) inductor is a case where a small amount of
inductance is much better than too much, because instability can ensue
with too much series feedback (too large an emitter (source) inductor).)

Has anybody actually used noiseless feedback with these devices at
VHF? After all, the fT of these SiGe transistors are in the 30 GHz+
range, so I would guess that the parasitics would mess the situation
quite badly, especially when using feedback components.

How critical is the layout compared to for instance MAR-x series MMICs
(that are essentially darlingtons) ? Can these SiGe transistors used
with dual sided boards and microstrips or do they require multilayer
boards and full striplines in order to use feedback ?

Paul OH3LWR

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