The question is a touch ambiguous, however BJTs excel where the tranconductance characteristics of the device are an important factor in an application.what are the limiting conditions where FET cannot replace BJT?
need to submit an assignmnt in college
At the gate of a FET, it is always supposed that there is no current entering the gate. The thing is, ate the gate, it acts like all semi-conductors. You'll find, at very high frequencies the some current may pass through it. Look for the "Miller effect" on the internet or for the large-signal circuit of a FET or the frequencial small-signal of FETs. Sedra and Smith have a book on that too. Almost gave you the answer there... you'll learn a lot by searching for these words... *cough* Miller*cough* effect...she said that in 99% cases an FET can replace a BJt.. but in 1% case it cannot be replaced. that case is related to frequency i.e. till a particular frequency both work/ fet works( i dnt remebr exatly). and beyond that BJt works. so i have to find information regarding that banwidth and frequeny. i gave her the comparison btwn the two but shes unhappy about it and demanding for a new assignmnt.
I don't believe I mentioned frequency.little more specific regardin the frequency
By this I meant the pinchoff or cutoff voltage of a JFET. By comparison the Vbe voltage of a BJT is pretty well rock solid.very much larger spread of (important) parameters