Displaying gray shades in passive matrix LCDs using successive approximation

Abstract

The gray shades to be displayed in each pixel are represented as a g bit binary number and g time intervals are used to display any one of the 2g gray shades. Amplitudes of the row and column waveforms of a passive matrix LCD are varied in different time intervals depending on the bit value of the gray shade data. Row and column voltages are reduced by a constant factor 1/√2 as one scans the display using the most significant bit to the least significant bit. This results as a variation of RMS voltage across the pixels depending on the data and hence its gray shade. This has been achieved without any compromise on the selection ratio. In fact the standard driven used for displaying bi-level (no gray shades) information are adequate if the voltage level generator is modified. For a given number of gray shades the flicker in the display is substantially less as compared to frame rate control method of displaying gray shades. Successive Approximation method has been used in conjunction with multi-line addressing (MLA) so to keep supply voltage low. The paper will describe the technique and present the experimental results.