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Why the drain negative voltage changed my bais?

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eladg

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reverse bais to fet

i built an lna with low power fet. it was single ended (one power supply , the gate is connected to gnd and sourse is connected to gnd throw resistor)

it work very good (vds =2v vgs =0.3v).
i made mistake and connectet to the drain negetive voltage.

the bais on the transistor (gaas ne321000 ) changed, and all the rf parameter changed what happend to me and why ? (the negetive voltage was 1v
 

Spasomat

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Sounds like your transistor was damaged.
If FETs are used outside the specified values they sometimes don't stop working completely. They sometimes just alter their S-parameters.
I would encourage you to change the FET.

Regards,

Spasomat
 

mr_ghz

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Hi eladg,

The negative voltage lead to a gate current flow what will destroy your GaAs FET immediately. Such FET's are very sensitive to wrong power supply and to electrostatic discharge. So you have to change it...

Bye
 

eladg

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Spasomat said:
Sounds like your transistor was damaged.
If FETs are used outside the specified values they sometimes don't stop working completely. They sometimes just alter their S-parameters.
I would encourage you to change the FET.

Regards,

Spasomat

there isnt any data about worng voltage so i donk know if it it outside the specified
 

eladg

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mr_ghz said:
Hi eladg,

The negative voltage lead to a gate current flow what will destroy your GaAs FET immediately. Such FET's are very sensitive to wrong power supply and to electrostatic discharge. So you have to change it...

Bye

why i get a curent at the gate ?

at all book that i looked i sow only positive Vds
 

mr_ghz

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Hi eladg,

The NE321000 is a junction-FET. This says that there is a PN-junction between the gate and the D/S channel. If you have a negative gate bias, this diode is in reverse direction. So the current is low (below some 10s uA). If you have a positive bias (or in your case a negative channel voltage) the diode is forward biased, what leads to a relatively high gate current. This gate current distroys the gate structure.

Bye
 

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