Analog Electronics
A JFET has disadvantage of

  having small gain-bandwidth product.
  having low input impedance.
  possessing positive temperature coefficient.
  being noisy.

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Analog Electronics
Voltage Series (feedback also called series-shunt feedback) results in

Decrease in input impedance & increase in output impedance
Increase in both input & output impedances
Decreases in both input & output impedances
Increase in input impedance & decreases in output impedance

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