Browse Prior Art Database

Retrace Circuit For Character Display

IP.com Disclosure Number: IPCOM000096359D
Original Publication Date: 1963-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Weber, EV: AUTHOR

Abstract

A cathode ray oscilloscope CRO electron beam can be returned to its home position as rapidly as possible consistent with circuitry after it has traced a display.

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Retrace Circuit For Character Display

A cathode ray oscilloscope CRO electron beam can be returned to its home position as rapidly as possible consistent with circuitry after it has traced a display.

Tracing deflection of the CRO beam is controlled by a trace current source connected to charge a capacitor C. The electron beam is returned to its home position by a retrace current source comprising transistors T1 and T2, also connected to charge the capacitor C. A monitor circuit, comprising transistors T3 and T4, controls the retrace current source to bring the voltage charge across C to a value necessary to return the electron beam to its home position.

Normally, the T3 base is held negative by the feedback path from the deflection amplifier so that T4 conducts and T3 does not. Therefore, T1 initially conducts while T2 is non-conductive. When the electron beam is to be placed in the home position, a negative retrace voltage pulse having a value corresponding to the home position, is applied to T4. This shuts off T4 and T1, causing T2 to supply charging current to C.

Increasing voltage across C, inverted by the deflection amplifier, is coupled back to the base of T3, eventually becoming sufficiently negative to cause T3 to go non-conductive again. This sends T4 into conduction, causing T1 to become conductive and T2 non-conductive. The flow of charging current to C stops when T2 is made non-conductive halting the beam at its home position.

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