How does the input impedance of a field-effect transistor (FET) compare with that of a bipolar transistor?

Field-Effect Transistors (FETs) are voltage-controlled devices. Their gate terminal is electrically isolated from the main current-carrying channel, which results in a fundamentally high input impedance. This means an FET draws virtually no current from the preceding circuit stage that drives it. In contrast, Bipolar Junction Transistors (BJTs) are current-controlled devices. Their base-emitter junction acts similarly to a forward-biased diode when turned on. This requires a continuous flow of base current to maintain conduction from collector to emitter, resulting in a comparatively low input impedance.