Re: mosfet RF amplifier with resistance

On Apr 21, 7:56 am, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Sat, 21 Apr 2007 11:14:15 +0200, Matteo <bassi.mat...@xxxxxxxxx>
wrote:



hi all!
I would like to project an amplifier with gain>20 and bandwidth of 1Ghz

I had to replace the ideal current generator over the drain with a
resistence and I tried to satisfied the specifications (gain and
bandwidth) but I found very strange values of current and voltage!

maybe these specification can not be satisfied with this circuit design
but..

can you help me to understand where I made the mistake?

here is my work:
http://www.thebags.it/listing/ampli/mosfet_resistence.PDF

thank you!
(sorry for my english)

I think that 20 GHz gain-bandwidth product is difficult, maybe
impossible for a simple 1-stage mosfet amplifier like this. You just
won't find a fet technology that will give you the required Gm without
a huge amount of capacitance, at least in silicon. Every semiconductor
technology has its limits.

Adding some inductances ("peaking") in various places can roughly
double GBW, but that's not an option if this is an all-IC design.

A compound-semiconductor phemt might be able to pull this off. They
have phenomenal transconductance and tiny capacitances. 20 GHz gbw is
easy in a single-stage bipolar MMIC, in InGaAs or SiGe.

John

Matteo,

as many others mentioned , it seems that the requirements
( GBW = 20 GHz , Cload = 250 pF) are too hard for a single transistor.

you may look at something like a cascode plus a follower-
buffer, or something like a Cherry-Hopper amplifier.

Jure Z.


.

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