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VCOM and Reference Voltage Source Circuit for TFT LCD Display

IP.com Disclosure Number: IPCOM000013339D
Original Publication Date: 2001-Oct-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 3 page(s) / 56K

Publishing Venue

IBM

Abstract

Disclosed is a circuit for generating Vcom and reference voltages for TFT LCD display module. The circuit is intended for reduce the product cost without suffering the display image quality. Figure 1 shows the simplified electrical configuration of a conventional TFT LCD display module. In this example, the module is designed on DC supplied Vcom technic and bi-level gate line driving method. Signal Line Driver

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VCOM and Reference Voltage Source Circuit for TFT LCD Display

Disclosed is a circuit for generating Vcom and reference voltages for TFT LCD
display module. The circuit is intended for reduce the product cost without
suffering the display image quality.

Figure 1 shows the simplified electrical configuration of a conventional TFT
LCD display module.

In this example, the module is designed on DC supplied Vcom technic and
bi-level gate line driving method.

Signal Line Driver

Vref2

Yv2

Vref3

Vref1 Vrefk

Yv1

Vcom

G1 G2 G3 Gk

XOUT1 XOUT2 XOUT3 XOUTm

Gate Line Driver

X1 X2 X3 Xm Y1
Y2
Y3Yn

Vcom

YOUT1 YOUT2 YOUT3

YOUTn

YV1

YV2

TFT Array

PCB

Figure 1, Simplified Electrical Configuration of Conventional TFT LCD display module

The TFT LCD display module is equipped with the following voltage sources.

Group of reference voltage sources for TFT LCD signal line driver(s) named

Vref1, Vref2,...Vrefk in figure 1
Group of reference voltage sources or power supplies for TFT LCD gate line

driver(s) named YV1 and YV2
Voltage source for common electrode on TFT LCD array named Vcom


1.


2.


3.

The first group of reference voltage sources defines the relationship between
digital data which represents luminance of pixels and physical voltage which
is applied to each pixel through signal lines on TFT array. Typical products
have 4 to 18 voltage sources in the group of the reference voltage source.
The second group of reference voltage sources or power supplies regulates the
output voltage of the gate driver for each output state. In the figure, two
voltage sources Yv1 and Yv2 are depicted assuming bi-level gate line driving
waveform. One is to regulate high voltage for turning on the TFT and the other

1

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for low voltage for turning it off.
Vcom voltage source provides common electrode voltage of TFT array.
Each voltage source is usually implemented by a series regulator circuit, a
shunt regulator circuit or a resistor divider circuit.

In a TFT LCD display module, quality of the voltage sources such as voltage
fluctuation resulted from dynamic load transient or input voltage transient,
or other voltage fluctuation including induced noise or oscillation, is a
vital matter to keep the quality of display images in good condition. Poor
quality on these voltages will result in unintended deteriorate of display
image such as crosstalk, flicker, or screen noise.

Since the reference voltages for the signal line driver(s) and Vcom electrode
voltage are directly applied to liquid crystal cells, perform...