In a dual-gate MOSFET, an additional second insulated gate is provided as compared to a conventional MOSFET. The flow of current through the MOSFET is controlled by voltages at both the gate terminals. Since the control is exerted by two gates, the dual-gate MOSFET may be considered to be the counterpart of a tetrode. Figure below shows the cross-section of an n-channel dual-gate DE-MOSFET.
Cross-section of an n-channel dual-gate DE-MOSFET
Figure below shows the circuit symbol of a dual-gate MOSFET.
Circuit symbol of an n-channel dual-gate DE-MOSFET
Dual-gate MOSFET acts if two MOSFETs are connected in series. The n+ region in the middle acts as the drain for MOSFET-1 and the source for the MOSFET-2. Both the gate voltages control the flow of current through the MOSFET. The drain current decreases when the gate voltage at either of the two gate terminals is made negative. It may be mentioned here that the gate terminal-1 provides higher transconductance as compared to the gate terminal-2. Owing to simultaneous control of two gate voltages, the device is used in applications such as AGC amplifier, mixers and demodulators. When it is used in AGC amplifier, the signal to be amplified is connected to Gate-1 and the voltage to control the gain is applied to Gate-2.
Figure below shows the transfer characteristics of a popular n-channel dual-gate DE-MOSFET. The drain characteristics are similar to that of a conventional n-channel DE-MOSFET.
Transfer characteristics of an n-channel dual-gate DE-MOSFET