Lecture 26

Lecture 26 - EEE 539Lecture 26 Junction FETs Our previous...

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EEE 539—Lecture 26 Junction FETs Our previous FET discussion was for the MOSFET, where the gate voltage created an inversion layer at the surface, which then connected the source and drain contacts to pass current. This was called an enhancement mode device. The junction FET (JFET) is a simpler device, and is a depletion mode device. This device operates like a clamp on a hose, gradually shrinking off the channel in which the current flows.
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In fact, the JFET was one of the earliest FETs developed, much before the MOSFET. The principle of operation relies upon the p-n junction, and its width. E v E c FERMI LEVEL E F p-TYPE REGION n-TYPE REGION eV bi
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For our purpose, we desire a one-sided p-n junction, i.e. This leads to Nearly all the depletion is in the n -type region. P-TYPE N-TYPE N D -N A -x p x n CHARGE DENSITY - - - + + +
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n n For V GS < 0, the p-n junction is reverse biased. As the gate bias is increased (negatively), the width of the depletion region increases. This squeezes off the channel region,
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This note was uploaded on 10/28/2009 for the course EEE 352 taught by Professor Ferry during the Fall '08 term at ASU.

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Lecture 26 - EEE 539Lecture 26 Junction FETs Our previous...

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