In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?

In standard schematic symbols for MOSFETs, an N-channel device is identified by the arrow on the substrate (bulk) pointing inward toward the channel. Conversely, a P-channel device has an outward-pointing arrow. A dual-gate MOSFET specifically features two separate gate terminals, which are drawn as two distinct lines parallel to the channel. This component is widely used in RF mixers and automatic gain control (AGC) amplifiers because the second gate allows for independent control of the gain. Symbol 4 in Figure E6-1 displays these exact characteristics: an inward-pointing arrow indicating an N-channel device, and two separate gate inputs. Distractor symbols usually show P-channel devices or single-gate configurations.