Flag: A voltage that indicates an event has taken place. Typically, a low voltage means the event has not occurred, while a high voltage means that it has. The output of a comparator is an example of a flag.

555 timer: A widely used circuit that can run in either of two modes: monostable and astable. In monostable, it can produce accurate time delays, and in astable it can produce rectangular waves with a variable duty cycle.

Field-effect Transistor: A transistor that depends on the action of an electric field to control its conductivity.

FET Colpitts oscillator: An FET oscillator in which the feedback signal is applied to the gate.

Experimental Formula: A formula or an equation discovered through experiment or observation. It represents an existing law in nature.

Error Voltage: The voltage between the two input terminals of an op amp. It is identical to the differential input voltage of the op amp.

Epitaxial Layer: A thin, deposited crystal layer that forms a portion of the electrical structure of certain semiconductors and integrated circuits.

Enhancement-mode MOSFET: A FET with an insulated gate that relies on an inversion layer to control its conductivity.

Emitter Follower: Identical to a CC amplifier. The name emitter follower caught on because it better describes the action. The ac emitter voltage follows the ac base voltage.

Emitter Diode: The diode formed by the emitter and base of a transistor.

Emitter Bias: The best way to bias a transistor for operation in the active region. The key idea is to set up a fixed value of the emitter current.

Emitter: The part of a transistor that is the source of carriers. For npn transistors, the emitter sends free electrons into the base. For pnp transistors, the emitter sends holes into the base.

Electromagnetic Interference (EMI): A form of interference resulting from the radiation of high-frequency energy.

Efficiency: The ac load power divided by the dc power supplied to the circuit multiplied by 100 percent.

Duty Cycle: The width of a pulse divided by the period between pulses. Usually, you multiply by 100 percent to get the answer as a percentage.