DC bias point shift - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

kris
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

Top

IR
Post subject: Posted: Wed Jan 11, 2006 5:15 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello kris,

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?

_________________
Best regards,

- IR

Posted 11/12/2012