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IM Products from HEMT - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


ljoseph
Post subject: IM products from HEMT Posted: Tue Oct 09, 2007 5:55 pm

Captain


Joined: Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
Hello

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.


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IR
Post subject: Posted: Wed Oct 10, 2007 2:43 pm

Site Admin


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


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stef
Post subject: Posted: Mon Nov 26, 2007 5:10 am

Lieutenant


Joined: Mon Nov 26, 2007 4:42 am
Posts: 4
Location: France
yes,
all kind of self-biaising effects will occur.




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