JFETs Junction Field Effect Transistors

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JFETsJunction Field Effect Transistors

• Rick Matthews
• Department of Physics
• Wake Forest University

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Beyond Bipolar

• Bipolar transistors (NPN and PNP) require a base
  current, typically microamps.
• Input impedance is limited because the
  base-emitter junction is forward biased in normal
  operation.
• Forward bias means current.
• We can do better.

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JFETS
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Current-voltage characteristics
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Designing an amplifier
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Load line
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Summary JFET vs. BJT

• JFET gives higher input impedance than BJTs.
• Input current in the nanoamp range or less, much
  smaller than BJTs.
• Power dissipation is less.
• Can work to higher frequencies.
• Easier to fabricate on ICs than BJTs.
• BUT lower voltage gain.