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: IM products from HEMT Posted: Tue Oct 09, 2007 5:55 pm
Joined: Tue Sep 04, 2007 7:54 am
i was evaluating performance of a HEMT device. This device has OIP3 of around 40 dBm. I am applying tow tones so that the output tone level of each tone is 5 dBm. The third order IM level is around -65 dBm so that OIP3 is 40 dBm. But when I remove DC power from the device the the Tones at the ouput drops to -17 dBm from +5dBm and the IM tsignals are going up to -40dBm....Don't understand why the third order IM signals are going up when DC power is removed from the HEMT. FYI this is a enhancement hEMT and works on positive bias at gate.
Post subject: Posted: Wed Oct 10, 2007 2:43 pm
Joined: Mon Jun 27, 2005 2:02 pm
When you operate the device under supply voltage, you provide the right DC operating point for the device. This DC operating point assure that the device will work in a linear mode (Class A probably) to avoid distortions.
If you remove the DC supply, then the only bias is provided through the RF signals which have low voltage, and therefore can not set a DC operating point.
Your device without supply voltage is in an undefind condition, hence you can expect abnormal output signals.
Post subject: Posted: Mon Nov 26, 2007 5:10 am
Joined: Mon Nov 26, 2007 4:42 am
all kind of self-biaising effects will occur.