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. Top 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. Top 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.
Posted 11/12/2012
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