difference between bjt and fet?
Although EE's will shoot me for this...
An easy way to look at it is this.
In an FET, the gate is insulated from both the source and the drain by a very large resistance. Hence, there is no current flow into the gate. Therefore, it must be a voltage-controlled device. Specifically, the channel resistance is a function of the gate to source voltage. Incidentally, that high resistance looking into the gate makes for a nasty capacitor to charge, hence the need for FET drivers on occasion. However, you also get essentially an open circuit for a load for the source driving the FET's gate.
In a BJT, the base is connected to the emitter via an internal resistance. The resistance is in the low ohms. Therefore, there is a means for current flow. Hence, the BJT is a current-controlled device. Specifically, the current through the device (collector to emitter -- assuming an NPN) is a function of the current into the base. And, since you have current flow through the device and some Vce, like the FET's drain to source, you have a resistance, collector to emitter. Since there is a low value resistor looking into the base of an on transistor, you end up with a rather low input impedance, an impedance that can be increased via increasing the emitter resistor.
I know it's a very simplistic view, but it works for me.
One other thing I think is neato about FET's is, since it is a true resistance between the drain and the source and not just a current through a voltage drop, you can literally measure an FET's resistance via an ohmmeter connected d-s or s-d. Just apply a voltage across the g-s leads and then measure the resistance between d and s. Hence, analog switches are more doable with an FET.