Post subject: down mixer Posted: Thu Oct 19, 2006 2:54
Joined: Thu Oct 19, 2006 2:42 am
iam a novice to this RF
I am doing a down mixer( active, folded mixer).
I am facing a huge difficulty in meeting gan and noise figure specs.
it is a low IF receiver structure.
1)How can I get a good
noise figure with out losing the gain??
2) How to measure
the output DC offset for the mixer??
Post subject: Active mixer noise figurePosted: Thu Oct 19, 2006
Joined: Wed Feb 22, 2006 3:51
One problem that mixer designers
often encounter with noise figure is that all mixers (except specially-designed
"image reject mixers") quite happily down-convert noise from the
image frequency as well as the desired frequency. In a low-IF system,
you can't filter out the image frequency. That means that even with
perfect devices, you'd have a baseline 6 dB noise figure - and it
would get worse from there.
In general, the rule is that
resistance is the source of noise. In a BJT, that particularly means
rbb', in FETs you have channel resistance. A good noise figure in
a mixer is hard to get - which is why the standard design for an
RF system establishes the noise figure in the pre-mixer LNA.
DC offset can occur because of device mismatching or lack of
symmetry - are you designing an IC or a discrete circuit? DC offset
can vary with signal amplitudes - what condition drives your spec?
Posted: Fri Oct 20, 2006 5:39 pm
Fri May 19, 2006 5:01 am
Just a quick thought: dual conversion? This will
yield better image rejection.
Post subject: mixer dc offsetPosted:
Fri Oct 27, 2006 9:16 am
Joined: Thu Oct
19, 2006 2:42 am
this mixer is
for a radio IC.
iam using spectreRF for my simulations.
to measure the DC offsets for my down conversion mixer??
have any paper(s) related to its measurement, pls post them..