How does self bias amplifier work?

How do self bias amplifier works?

Thanks

Re: GaAs FET

plz post subject name in relation with ur content
anyway GaAs IS HAVING CERTAIN SUPEERMACY OVER SI AND GE IN THE CASE OF MOBILITY. ALSO IT BELONGS TO COMPOUND SEMICONDUCTORS




SELF BIAS CAN BE USED FOR JFET DEVICES

Re: GaAs FET

bouchy,
Self bias refers to any biasing scheme where an external source of bias voltage (or current) is not required.
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In a FET amplifier, this is accomplished by using a resistor between the source and ground (common). Consider an N-channel FET, either JFET or MOSFET. AsS the drain current increases, the voltage across the source resistor increases, thus reducing the Gate-Source voltage, which tends to couneract the effect of the drain current increase. This is negative feedback.
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Consider a bipolar (NPN in my example) amplifier with a collector resistor. Connect another resistor (the bias resistor) between the collector and the base. Now, as th collector current increases, the collector voltage decreases, resulting in a lower voltage across the bias resistor, and, therefore lower base current. The lower base current couneracts the increase in collector current. Again, this is negative feedback.
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Regards,
Kral

Re: GaAs FET

but anyway in the case BJT
selfbias is having certain defects ...stability....
so that we are going for universal bias or voltage divider bias circuit