A voltage that is a predetermined function of time and that is used to deflect the electron beam of a cathode-ray tube so that the luminous spot traverses the screen in a desired manner. One complete traverse of the screen, usually in a horizontal direction, is termed a sweep.

The most common type of timebase is one that produces a linear sweep: a sawtooth waveform is used to effect this. The circuit that produces the required voltage is a timebase generator; it may be free-running, in which a periodic sawtooth waveform is produced, or it may be clocked, when one sweep is produced on application of a trigger pulse to the circuit. The period during which the spot returns to the starting point is the flyback and in many applications, such as in television receivers, the flyback is suppressed, i.e. no luminous spot is observed on the screen during the return interval. The sweep frequency is the repetition rate of the sweeps across the screen.

A Miller sweep generator is a timebase generator that contains a Miller integrator in the circuit in order to improve the linearity of the sweep. In some applications it is necessary to produce a timebase in which the electron beam moves at a faster speed during part of the sweep, termed an expanded sweep. An expanded-sweep generator is one in which the incremental output voltage with respect to time is greater during a portion of the sweep in order to produce such an expanded sweep. A delayed sweep is a sweep produced by a synchronous timebase generator in which a predetermined delay time is introduced between application of the trigger pulse and commencement of the sweep on the screen.

Timebases are used to control the spot on the screen in many applications. Cathode-ray oscilloscopes usually contain a circuit that generates a free-running sawtooth waveform with an adjustable sweep frequency. Radar systems use a synchronized timebase that is controlled by the transmitter so that each sweep is synchronized with the transmitted pulses and the return echo appears at a distance along the trace determined by the distance of the target from the transmitter. Television systems employ timebases in the camera tubes and in the receivers to scan the lines and frames. The timebase in the receiver is usually controlled by synchronizing pulses in order to retain the correct relationship to the transmitter; alternatively a flywheel timebase is sometimes used in which the frame frequency is controlled by the electrical inertia of the circuit. This eliminates the need for frame-synchronizing pulses.