many FET power transistors have this character. The possible reason is Vgs is shifting when the PA is powered up to P1dB. You can measure this change with a multimeter (my experience is Vgs will be changed to more than 100%, and the shifting range is related with matching circuit design). The change of Vgs changed gain. The physical reason of gain expansion however I am not very clear.
such expansion is more prominent in high power FETs than low power FETs; for example , 40W FET is more easy to exhibit gain expansion than 10W FETs
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发表于 2008-11-16 17:43:46
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