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Reference Voltage and Common Voltage Supply Circuit for TFT LCD Display Mudule Disclosure Number: IPCOM000015390D
Original Publication Date: 2002-Mar-06
Included in the Prior Art Database: 2003-Jun-20

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In TFT LCD display which uses DC sourced Vcom voltage(voltage applied to common electrode in TFT array) , it is important to keep the constant relation between each Vref voltages(reference voltages supplied to D/A converters in data line driver) and Vcom voltage in order to minimize image flickering and/or horizontal crosstalk. To supply stable Vcom voltage is difficult part of the product design because the load current of the Vcom electrode on the TFT array is dynamically changed with large amplitude. On the other hand , to supply the stable Vref voltage is relatively easy because the load current of these voltage is stable. In these reason, it is reasonable to generate Vref voltages referenced to Vcom voltage which has relatively poor dynamic load response. On the type of TFT array design in which the storage capacitance is implemented between Vcom electrode and pixel electrode, Vcom voltage must be adjustable for optimum voltage to minimize screen flickering. Once the Vcom voltage has been trimmed to the optimum voltage, relation (voltage difference) between the Vcom voltage and Vref voltages must be constant. Concept of traditional implementation of this scheme is shown in Figure 1. DIFFn: SUBTRACTER SUMn: ADDER An: Output Stage (Unity gain voltage follower in this case) Figure 1 Traditional implementation