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System of LCD Display
Y
Y
0
1
The amplification operation of a transistor is used for the TFT switch in the active matrix system. In this
system, switching speed is unified over the whole display, increasing drive response speed as compared
with the passive matrix system. Therefore, TFT LCD display (active matrix system) is adopted for the
highly efficient display, which can provide the response speed required for big screens or quickly moving
pictures. However, further response speed is needed for high definition LCD television. This will be
described later.
5-6 Drive of Active Matrix System
The TFT LCD display consists of a matrix of n lines of X direction (X0 - Xn-1) and of n rows of Y direction
(Y0 - Yn-1). The line of X direction is called the "gate line" and the line (row) of Y direction is called the
"data line."
First, the scan is started from the pixel address
(X0, Y0), and when the address (X0, Yn-1) is
selected the scan of X0 line is completed. Next, all
the pixels from X1 line to Xn-1 line are scanned in
sequence, and the final address is (Xn-1, Yn-1).
The operation of selected pixel address (X1, Y2)
is explained below.
First, (signal) voltage is supplied to X1 line (gate
of TFT), next voltage is supplied to Y2 row (source
of TFT), and the address of the intersection of X1
line and Y2 row is selected and its TFT is turned
On or Off. However, just switching the TFT on and
off will not change the brightness of the screen.
The brightness of a screen is changed by control-
ling the voltage of a data line (Y row). Fig. 19
shows the voltage characteristic of the matrix sys-
tem.
Y
Y
2
3
-19-
X0
TFT (Switch)
Liquid Crystal
COMMON Electrode
X1
X2
The LCD shutter is operated by
TFT at the address (X1, Y0).
X3
Fig. 18
Structure of TFT Matrix
Since the time for the drive voltage to reach its
required value is shorter in the active matrix system,
the response time of the display becomes quicker.
Active Matrix System
Fig. 19
Voltage Characteristic of Matrix System
Training Manual Principle of LCD
Passive Matrix System
Time
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