Re: what is a Gm stage?
- From: PeteS <axkz70@xxxxxxxxxxxxx>
- Date: Thu, 31 May 2007 21:21:33 -0400
tedthornton11@xxxxxxxxxxxxxx wrote:
Hi,
I'm trying to figure out how to implement a Gm stage. I understand the
basic idea - voltage in, current out - and I've seen some figures like
(a) and (b) shown in the following diagram, ie. a differential pair
with no load representing a Gm stage:
http://farm1.static.flickr.com/223/523614745_fc290139dd_b.jpg
But I'm not sure what exactly to do with this differential pair with
no load. I Can I just use the iout+/- from the differential pair
directly as the inputs to the next stage? Or do I need a load for the
differential pair? And what could I use as the load? I thought about a
current mirror, as in (c), but that means it's just an voltage
amplifier - the current never goes "out" of this stage, it just gets
redistributed between the input transistors. This seems wrong (???).
Perhaps some DC current sources (with common mode feedback for the
biasing), as in (d). Then the iout current due to a change in Vin is
forced out to the load? But isn't this just a differential amplifier?
Thanks for your help,
Ted
A Gm stage is what you have stated but not realised; a forward transconductance stage. As you correctly surmise, it is an amplifier, but specified by it's Io vs. Vin characteristics rather than some other parameter.
I didn't open your link, but maybe that helps.
Cheers
PeteS
.
- References:
- what is a Gm stage?
- From: tedthornton11
- what is a Gm stage?
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