Browse Prior Art Database

1H/2H/7H/9H/11H Counter Electrode Drive Method for TFT-LCD

IP.com Disclosure Number: IPCOM000112432D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 108K

Publishing Venue

IBM

Related People

Itoh, H: AUTHOR [+4]

Abstract

Disclosed is a LCD Drive method which can make Low Power dissipation and keep screen quality.

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1H/2H/7H/9H/11H Counter Electrode Drive Method for TFT-LCD

      Disclosed is a

LCD Drive

method which can make Low Power
dissipation and keep screen quality.

      Generally to prevent DC Bias charge into TFT-LCD Capacity, Vcom
(and also Vs) Counter Electrode drive which means driving Electrode
+/- alternatively is used as shown in Fig. 8 and Fig. 4.

      In view of Power dissipation, because TFT-LCD Vcom capacity
C(Cst+Clc) is considerable value (refer to Fig. 3), by reducing
frequency of Vcom Counter Electrode drive for TFT-LCD, the power
dissipation becomes lower.

      For example, it becomes 1/2 Watt (actual) lower by reducing
Vcom drive frequency from normal 1H (it means 1Hsync each, and
f=15.75kHz) counter drive to 2H (it means 2Hsync each, and f=7.88kHz)
counter drive, as shown in Fig. 1.

      However, in view of FOS (front of screen) quality, "Reduced
Frequency of Vcom counter drive (2H counter drive)" seems to be
inferior to Normal "1H counter drive" as the following 2 reasons.

      1) If it use "Reduced Frequency drive", a boundary stripe is
visible at the boundary where Vcom electrode is driven +/-
alternatively, because brightness at each line corresponding to the
frequency is slightly different due to C (Cst+Clc) charge decay.

      2) The boundary stripe is located physically in the horizontal
fixed position on the screen of 640(H) x 480 (V) LCD panel (Fig. 2),
it can not be accepted as FOS quality because it's visible when the
boundary stripe pitch is more than 2Hsync (approximately 0.66mm
pitch).

      So, in order to get not only Low power dissipation but also
screen quality, this New LCD drive method solves above two items by
the following.

Case 1) By using "Reduced Frequency drive of the prime number (for
640(H) x 480(V) LCD panel) of Hsync line", the boundary stripe is
lo...