Question

differences between bjt and jfet

Answer 1

One difference the BJT's have an exponential relationship and the JFET's have a square law relationship.
There input impedance are different BJT's have a fairly small input impedance when compared to JFET's
Biasing consideration are slightly different as well as there small single models

Answer 2

Very simply put, a bjt stands for a "bipolar junction transistor" while a jfet stands for "junction field effect transistor". The fundamental difference between the two is how they work. A BJT is said to be a current controlled transistor where the base current iB, its magnitude and phase determine the output of the transistor (ofcourse when the bjt is in active mode). A JFET on the other hand, is a voltage controlled device ie, the output is determined by the gate voltage magnitude and phase. One more important point of difference is that the BJT, when in saturation, switches faster than any FET. it's dynamic response is great, but the power consumption is greater still, which is kinda bad in today's electronics. FET, switches slower in comparison to the BJT, but consumes less power. the h-parameter model of the BJT shows an input resistance if 1100 ohms while that of the JFET is infinite or sufficiently large. Other differences include the fabrication styles, structure and the geometry of the devices, maximum gains that each one can provide.