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LCD Driving Circuitry: Multiplex

Blaze Display Technology Co., Ltd. | Updated: Oct 28, 2015

   【R&D Department of Blaze Display】The configuration for Liquid Crystal Display Multiplex Drive technique differs from a Static Drive technique is that it uses more than a single "backplane" or segment common. With this configuration, each segment control line can be connected to as many segments as there are backplanes, providing that each of the segments that it is connected to are tied to a separate backplanes. This method "Multiplexes" each of the segment control lines and minimizes the number of interconnects. This is the method used with complex displays that have limited interconnection surface area or available drive circuits. This reduction in the number of external connections enhances device reliability and increases the potential display density. The liability of a higher multiplex rate will effect display quality, operational temperature range, and the increased complexity of drive circuitry (or perhaps microprocessor software) may necessary for their operation.

    The method of drive for multiplexed displays is essentially a time division multiplex with the number of time divisions equal to twice the number of common planes used in a given format. As is the case with conventionalLCDs, in order to prevent irreversible electrochemical action from destroying the display, the voltage at all segment locations must be caused to reverse polarity periodically so that zero net DC voltage is applied. This is the reason for the doubling in time divisions: Each common plane must be alternately driven with a voltage pulse of opposite polarity.

    As is the case with non multiplexed displays, the drive frequency should be chosen to be above the flicker-fusion rate, i.e. >30 Hz. Since increasing the drive frequency significantly above this value increases current demand by the CMOS drive electronics, and to prevent problems due to the finite conductivity of the display segment and common electrodes, an upper drive frequency limit of 60-90 Hz is recommended.

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