Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: down mixer Posted: Thu Oct 19, 2006 2:54 am
Joined: Thu Oct
19, 2006 2:42 am
iam a novice to this RF design field.
I am doing
a down mixer( active, folded mixer).
I am facing a huge difficulty in meeting gan and noise figure specs.
is a low IF receiver structure.
1)How can I get a good noise figure with out losing the gain??
How to measure the output DC offset for the mixer??
Post subject: Active mixer
noise figurePosted: Thu Oct 19, 2006 3:47 pm
Joined: Wed Feb 22, 2006 3:51 pm
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.
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?
subject: Posted: Fri Oct 20, 2006 5:39 pm
Joined: Fri May 19, 2006 5:01 am
Just a quick thought: dual conversion? This will yield better image
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.
how to measure the DC offsets for my
down conversion mixer??
if u have any paper(s) related to its measurement, pls post them..