DC bias point shift - RF Cafe Forums
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 Facebook page, please do.
Below are all of the forum threads, including all the responses to the original posts.
Post subject: DC bias point shift Posted: Fri Jan 06, 2006 2:41 am
When I run DC simulations I see that my DC bias point is correct for my PA but when I run Harmonic Balance simulations my output waveforms are centered around at completely different point (basically at VCE=0)...how is this possible?? what could be the problem and how should I go about correcting it. I've read some things about bias point shifts but this seems completely odd. As far as I can see my DC/AC blocks are in the right places so I just don't understand what's going on??? actually, after running HB simulation i plotted the current going through the collector and it showed a significant value instead of showing 0 because of RFC at the collector. i increased the value of the RFC inductor but still same problem exist....any suggestions
Post subject: Posted: Wed Jan 11, 2006 5:15 pm
Joined: Mon Jun 27, 2005 2:02 pm
My guess is that your PA is working in a class which is not class A. So when you run HB simulations and sweep the input power you see that your current and voltage are swept to extreme points. To which extent it happens, I can´t tell without knowing how your PA works, i.e. exactly which class and actual quiescent operating point?
Could you share some details about these issues of your design?