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

The input impedance of a field-effect transistor (FET) is significantly higher than that of a bipolar transistor. This characteristic arises from the operational principles of these two types of transistors.

FETs are designed to control current using an electric field. They have very high input impedance, often in the range of megaohms or even higher. This means that they draw very little current from the source driving the input, making them ideal for sensitive applications where loading effects must be minimized.

In contrast, bipolar transistors involve current flow through two types of semiconductor materials, which leads to lower input impedance. Typically, the input impedance of a bipolar transistor is in the kiloohm range, which is markedly lower than that of an FET. This higher input current draw can affect the overall circuit performance, particularly in applications requiring precise control and signal integrity.

The distinction in impedance between the two types of transistors is crucial for circuit design, as it affects how the transistors interact with previous circuit stages and the overall behavior of the circuit. Thus, the assertion that an FET has high input impedance while a bipolar transistor has low input impedance is correctly stated.