Digital driving implementation at multiple reference light intensities

Abstract

A driver system for driving pixels of an active matrix display and a method related thereto are disclosed. The driver system comprises at least one power supply line pair having first and second powersupply lines (311, 312). Each power supply line pair comprises an ordered sequence of contact point pairs (306, 307) distributed over its length. Circuit elements (300, 400) are connected to a data line (313) and to the contact point pairs. During use, the circuit elements are driven at pre-determined current levels through its corresponding contact points, there being at least three such pre-determined current levels selectable via a received data signal. Also provided is a voltage drop calculation unit (30) for calculating voltage drops at the level of each circuit element. A voltage drop causing a deviation of the current levels from their pre-determined values, at least one voltage drop compensation unit (109, 119) is provided for compensating the calculated voltage drops at each circuit element by way of providing a data compensation signal on a data line. A method of calibrating voltage drop compensation signals is also described.

Description

technical field [0001] The present invention relates to the field of digital drive methods and circuitry for active matrix displays such as active matrix light emitting diode displays (AMLED) or active matrix organic light emitting diode displays (AMOLED). Background technique [0002] In an active matrix display, each pixel has an associated pixel driver circuit adapted to control its light output by driving current through a light emitter (such as an OLED or LED) in a controlled manner ( For example, luminance or brightness). This is typically achieved by the drive transistor for which the gate voltage signal is controlling the leakage current injected into the light emitter. The analog drive method ensures continuous control over the drive current level and thus the brightness of the pixel. The drive current level is kept constant during the full frame period, and the drive transistors are typically operated in a saturation regime. The longer active time of a pixel whe...

AI Technical Summary

Problems solved by technology

However, many reasons may have an effect on the deviation of the driving current, resulting in the loss of image quality

Non-uniform manufacturing processes that manifest among these causes (e.g., non-uniform thickness of dielectric layers, doping concentration variations, grain boundaries in low-temperature polysilicon, etc.) but also aging, temperature-induced changes, and power supply during display operation voltage drop across the line, both adversely affect uniformity across the flat panel display

Patent application EP16197152.8 discloses a method of calibration and compensation for digitally driven active matrix displays which solves the problem of display non-uniformity caused by resistive voltage drops on supply lines

However, this method is only suitable for a limited color depth / number of gray levels because the duration of the shortest PWM pulse is limited by the RC time constant of the pixel driver circuit or the rise time (speed) of the PWM driver circuit, whichever is greater

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