Motorola Corporation

Michael P Bafaro

Theodore V Lester

James J Parker

A scanning CRT display system is disclosed in which transitions of a horizontal sync signal are directly utilized to provide control signals for driving a FET (field effect transistor) power drive device which controls horizontal deflection yoke current. Protection circuitry is provided such that the FET power drive device is turned off if excessive FET through current is sensed, and protection circuitry also prevents turning on the FET drive device if an excessively high flyback voltage is present at the drain terminal of the FET device. Linearization of the horizontal deflection yoke current is provided by effectively sensing the temperature variable on resistance of the FET output drive device and providing a compensation control signal in accordance therewith, wherein this compensation control signal controls the magnetization provided by a control winding on a saturable magnetic core on which a linearity compensation coil is also wound. The linearity compensation coil and the deflection yoke are connected in series and the compensation control signal effectively reduces the series inductance of these elements so as to provide linearity compensation for horizontal deflection yoke current.

Direct drive scanning CRT display system

Scanning CRT display system with linearity compensation

A dual slope pulse width modulation regulator for separate control of two independently operative power supplies is provided. An oscillator supplies a triangle wave having a period T signal to each of two separate DC comparators each of which also receives an analog error signal related to the difference between a power supply output signal and a predetermined reference level. The outputs of the DC comparators are coupled to a pair of AND gates which are alternately enabled by a digital output signal of the oscillator with the digital output signal having output states corresponding to the duration of first and second rates of change of the triangle wave signal which occur during each period T. The outputs of the AND gates correspond to pulse width modulated drive signals which are utilized to control the excitation of independently operative power supplies having output sensor circuits which sample the output of the power supplies and result in providing the first and second analog error signals. During each period T separate, independently operative pulse width modulation power supply control signals are provided through the alternate use of the first and second rates of change of the triangle wave signal of the oscillator to provide pulse width modulation control signals.

Dual slope pulse width modulation regulator and control system

An improved video amplifier arrangement with wideband D-C gain control is disclosed for use in a video display device of the type for displaying character information. The video amplifier includes an open-collector, TTL logic gate for receiving digital voice signal information which is then coupled to a cascode amplifier circuit for amplifying the video information and applying the same to a control element of an associated cathode ray tube. A D-C amplifier is provided having an adjustable element in its base input for applying a selectable D-C voltage thereto. The D-C amplifier includes an emitter resistor which is also connected to the open collector of the logic gate whereby the current developed by the D-C amplifier and applied to the emitter load resistor further determines the load current through the TTL logic gate. This, in turn, controls the level of pulse amplitude of the digital video information and serves as a video gain or level control.

Video amplifier arrangement with wideband D-C gain control

Dynamic focus circuitry for a CRT data display terminal provides high resolution even in the corners of the screen by means of a dynamic focus voltage which is the product of parabolic waveforms at horizontal line rate and vertical frame rate. The non-linear characteristic of a diode provides the product function at minimum expense.

Dynamic focus circuitry for a CRT data display terminal

Dynamic focus voltages for a CRT are obtained by utilizing the combined parabolic conversion wave shapes for control of the focusing electrode to provide sharp focus at all points in the raster. A current source is coupled to the focus divider chain and the conversion wave shape controls the current in the divider chain by controlling the resistance in a transistor. No high voltage capacitors are required since the dynamic voltages are coupled into the chain near the low voltage end.

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Park Ridge, IL, United States of America

Michael P Bafaro