A Successive Approximation Technique for Displaying Gray Shades in Liquid Crystal Displays (LCDs)

Abstract

A successive approximation technique that is based on the conventional line-by-line-addressing is proposed. A large number of gray shades can be displayed without flicker by using low-cost liquid crystal display drivers that are designed to drive the pixels to either ON or OFF states in bilevel displays.

Low Power Techniques for Gray Shades in Liquid Crystal Displays

“…This method can also be used reduce the power consumption and supply voltage of multi-line addressing techniques. Hardware complexity of the drivers of successive approximation techniques is the least of all the techniques for gray shades and a good reduction in power consumption and supply voltage of the driver circuit can be achieved without increasing the hardware complexity of the drivers with just a few analog multiplexers [2], [4]. These multiplexers are common to all stages of the drivers and therefore independent of number of rows and columns in the display.…”

“…Polarity of the select pulses is periodically reversed to ensure DC free waveforms across the pixels. This technique achieves the maximum selection ratio (defined as the ratio of RMS voltage across the ON pixels to that across the OFF pixels) as described in [4]. Principle of reducing power dissipation is described next.…”

“…Amplitude of select pulses is reduced by a factor to obtain the descending part of the select waveform. Power dissipated in the series resistor, when the capacitor in RC-circuit is charged and discharged with waveform of 'sequence-' is given by (4) The first term corresponds to transition from 0 to 1 and from 1 to 0 and the summation in the second term corresponds to rest of the transitions (5) Here again, corresponds to the transition to (or from) the select voltage corresponding to MSB from (to) the next significant bit and the simplified expression for the power dissipation in a resistor of an RC-circuit is (6) Power dissipation of 'sequence-b' is compared with that of the select 'sequence-' by taking the ratio of the expression in (6) to the expression in (3) and by assigning as in the case of successive approximation techniques [3], [4] (7)…”

“…The main objective of the work is to reduce power dissipation in LCDs for images with gray shades. Of the several techniques to display gray shades in LCDs, successive approximation techniques [3], [4] and wavelet-based techniques [5], [6] require less hardware to display a large number of gray shades and it is possible to reduce power dissipation of these techniques as described in this paper. Successive approximation technique that selects one address line at a time (SAT-L1) [4] is well suited for low power applications.…”

“…Of the several techniques to display gray shades in LCDs, successive approximation techniques [3], [4] and wavelet-based techniques [5], [6] require less hardware to display a large number of gray shades and it is possible to reduce power dissipation of these techniques as described in this paper. Successive approximation technique that selects one address line at a time (SAT-L1) [4] is well suited for low power applications. SAT-L1 can display gray shades in time intervals as compared to time intervals that are necessary in case of pulsewidth modulation [7] and frame rate control [8].…”