Electronic – Why are the advantages of JFET over MOSFET, or why are JFET still used


I saw JFET in an electret mic circuit, and it is quite recent, so I'm wondering why.

Since we are looking for the highest gate impedance, MOSFET would seem to be a better choice.

I've also read that JFET have got a flatter response because of a higher drain resistance. I don't even understand what the drain resistance is. Is it the source drain resistance? And what does it have to do with flattness?

And more generally, what are the advantages of JFET over MOSFET?

Best Answer

The JFET has several advantages over the MOSFET. The most important are:

  • higher gain
  • lower noise

These are the overriding factors when building preamplifiers for low-level signals, such as those from microphones.

Also, since there's no thin gate oxide that can be punctured by ESD, they're a little more "rugged" in that sense.