The BJT (Bipolar Junction Transistor) exhibits higher gain compared to the MOS (Metal-Oxide-Semiconductor) transistor. This difference arises because the BJT controls the current through its base terminal, while the MOS transistor regulates the current through its gate terminal.
The BJT functions as a current-controlled device, and its gain is defined as the ratio of the output current to the input current. Referred to as the beta (β) or hFE, the BJT’s current gain typically ranges from several tens to a few hundred. This elevated gain enables the BJT to amplify small input currents into larger output currents, making it well-suited for applications necessitating substantial current amplification.
In contrast, the MOS transistor functions as a voltage-controlled device. Its gain, expressed as the transconductance (gm), represents the ratio of the change in output current to the change in input voltage. The gain of the MOS transistor is usually lower than that of the BJT, ranging from a few millisiemens to a few tens of millisiemens. The MOS transistor is commonly employed in digital circuits and low-power applications where high current amplification is not the primary objective.