DC Beta (βdc): The ratio of the dc collector current to the dc base current.

DC Alpha (αdc): The dc collector current divided by the dc emitter current.

Darlington Transistor: Two transistors connected to get a very high value of β. The emitter of the first transistor drives the base of the second transistor.

Cutoff Region: The region where the base current is zero in a CE connection. In this region, the emitter and collector diodes are nonconducting. The only collector current is the very small current produced by minority carriers and surface leakage current.

Cutoff Point: Approximately the same as the lower end of the load line. The exact cutoff point occurs where base current equals zero. At this point, there is a small collector leakage current, which means the cutoff point is slightly above the lower end of the dc load line.

Cutoff Frequency: Identical to the critical frequency. The name cutoff is preferred when you are discussing filters because that's what most people use.

Curve Tracer: An electronic device for drawing characteristic curves on a cathode-ray tube.

Current Source: Ideally, this is an energy source that produces a constant current through a load resistance of any value. To a second approximation, it includes a very high resistance in parallel with the energy source.

Current Mirror: A circuit that acts as a current source whose value is a reflection of current through a biasing resistor and a diode.

Current Limiting: Electronically reducing the supply voltage so that the current does not exceed a predetermined limit. This is necessary to protect the diodes and transistors, which usually blow out faster than the fuse under shorted-load conditions.

Current Feedback: This is a type of feedback where the feedback signal is proportional to the output current.

Current-Controlled Voltage Source (ICVS): Sometimes called a transresistance amplifier, this type of negative feedback amplifier has the input current controlling the output voltage.

Current-Controlled Current Source (ICIS): A type of negative feedback amplifier in which the input current is amplified to get a larger output current, ideal because of stabilized current gain, zero input impedance, and infinite output impedance.

Current Booster: A device, usually a transistor, that increases the maximum allowable load current of an op-amp circuit.

Crystal: The geometric structure that occurs when silicon atoms combine. Each silicon atom has four neighbors, and this results in a special shape called a crystal.