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Below are all of the forum threads, including all the responses to the original posts. siva Post subject: down mixer Posted: Thu Oct 19, 2006 2:54 am Lieutenant Joined: Thu Oct 19, 2006 2:42 am Posts: 2 Location: india hi 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. 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?? Top fred47 Post subject: Active mixer noise figurePosted: Thu Oct 19, 2006 3:47 pm General Joined: Wed Feb 22, 2006 3:51 pm Posts: 104 Hello! 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? Good Luck! Fred Top Charl Post subject: Posted: Fri Oct 20, 2006 5:39 pm Colonel Joined: Fri May 19, 2006 5:01 am Posts: 25 Location: Netherlands Hi, Just a quick thought: dual conversion? This will yield better image rejection. Kind regards, Charl Top siva Post subject: mixer dc offsetPosted: Fri Oct 27, 2006 9:16 am Lieutenant Joined: Thu Oct 19, 2006 2:42 am Posts: 2 Location: india 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.. thank u.... Posted 11/12/2012 | ||||||
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