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# Linearity Correction for Cathode Ray Tube Display

IP.com Disclosure Number: IPCOM000079733D
Original Publication Date: 1973-Aug-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 47K

IBM

## Related People

David, RM: AUTHOR [+2]

## Abstract

A linearity correction method and circuit for a cathode-ray tube (CRT) yields design parameters, which are conducive to achieving accurate linearity correction with minimal circuit complexity.

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Linearity Correction for Cathode Ray Tube Display

A linearity correction method and circuit for a cathode-ray tube (CRT) yields design parameters, which are conducive to achieving accurate linearity correction with minimal circuit complexity.

Assuming uniformity in deflection yoke and CRT production, a plot of CRT electron-beam deflection versus yoke current is made. Typically, the plot is an S- shaped curve, such as curve 1 in Fig. 1. The left and right halves of curve 1 are closely approximated by equations (1) and (2), respectively, and result in a uniform deflection per unit time for display linearity. The values of constants in equations (1) and (2) may be determined by the method of least squares.

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The deflection circuit comprises a function generator and deflection yoke current driver. The function generator produces a voltage waveform of the correct shape for driving the deflection yoke current driver, which is a linear voltage controlled current source.

In the function generator circuit shown in Fig. 2, inverter X1 functions as a switch to discharge capacitor C1 through resistor R1 during retrace. Zener diode Z1, resistor R2, and transistor T1 assure that a virtually constant current flows through resistor R3. This current, less the base current of T1 and the collector current of transistor T5, serves as a charging current for Cl. Since the current through R3 and the base current of T1 are virtually constant, the rate at which C1 charges can be controlled by varying the collector current of T5.

Transistors T2, T3, and T4 and resistors R4-R13 function as a differential amplifier with transistors T6, T7, and resistor R16 serving as a buffer for feedback and output. Capacitor C3 allows AC coupling from the buffer to the differential amplifier. Capacitor C2 is designed so that the Thevenin's equivalent power...