Browse Prior Art Database

Reference Voltage and Common Voltage Supply Circuit for TFT LCD Display Mudule

IP.com Disclosure Number: IPCOM000015390D
Original Publication Date: 2002-Mar-06
Included in the Prior Art Database: 2003-Jun-20
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Abstract

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

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 3

  Reference Voltage and Common Voltage Supply Circuit for TFT LCD Display Mudule

   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

This disclosure introduces more simple implementation to realize the
purpose.

Fig 2. shows th...