Browse Prior Art Database

Video Driving Circuit

IP.com Disclosure Number: IPCOM000092633D
Original Publication Date: 1966-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Tech, DD: AUTHOR [+3]

Abstract

In circuits for providing composite video signals from two-level input signals, linear feedback amplifiers or mixers. These are usually employed to combine the video and synchronizing signals to provide a composite video signal for use with a display terminal. To provide the impedance matching and drive characteristics required to service a remote display terminal, an emitter-follower stage is normally required. A transistor connected in an emitter-follower configuration is employed in which the mixing of the two signals is done at the input to the emitter-follower. The latter also drives the impedance of a coaxial cable connecting the circuit to the display terminal.

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Video Driving Circuit

In circuits for providing composite video signals from two-level input signals, linear feedback amplifiers or mixers. These are usually employed to combine the video and synchronizing signals to provide a composite video signal for use with a display terminal. To provide the impedance matching and drive characteristics required to service a remote display terminal, an emitter-follower stage is normally required. A transistor connected in an emitter-follower configuration is employed in which the mixing of the two signals is done at the input to the emitter-follower. The latter also drives the impedance of a coaxial cable connecting the circuit to the display terminal.

In its normal state, i. e., without either input on, the circuit operates in a nonsaturated conducting state. The base of transistor 1 is maintained at approximately m5 volts by the voltage divider comprising resistors 3 and 5 and provides an output signal of approximately -4.5 volts. Positive video signals are applied to input terminal 7. Negative synchronizing signals are applied to input terminals 9. Positive and negative denote purely relative signal levels. When a positive video signal is applied to terminal 7, and input terminal 9 is at the down level or disconnected, the video signal is coupled through diode 11 to the base 13 of transistor 1. The base is raised to ground level, transistor 1 is turned off and emitter 15 rises to ground level to drive the coaxial transmiss...