Browse Prior Art Database

Driving Method for TFT/LCD Grayscale

IP.com Disclosure Number: IPCOM000102512D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Terazawa, S: AUTHOR [+2]

Abstract

Disclosed is a driving technique for displaying grayscale on a liquid crystal display addressed by thin film transistors (TFT/LCD) with fewer analog switches of the data-driver than the conventional method. This technique uses data-drivers which have analog multiplexers with disable terminals connected to datalines and reference voltage sources connected to input of analog multiplexers. These analog multiplexers are digitally controlled analog switches and each reference voltage source is altered 2 voltage levels during one gate pulse period (gate on period). The number of analog switches of one multiplexer is a half of the graylevels. To display M (2 to the Nth power) grayscale on TFT/LCD, the number of voltage sources is M/2 (2 to the (N-1)th power).

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Driving Method for TFT/LCD Grayscale

       Disclosed is a driving technique for displaying grayscale
on a liquid crystal display addressed by thin film transistors
(TFT/LCD) with fewer analog switches of the data-driver than the
conventional method.  This technique uses data-drivers which have
analog multiplexers with disable terminals connected to datalines and
reference voltage sources connected to input of analog multiplexers.
These analog multiplexers are digitally controlled analog switches
and each reference voltage source is altered 2 voltage levels during
one gate pulse period (gate on period).  The number of analog
switches of one multiplexer is a half of the graylevels. To display M
(2 to the Nth power) grayscale on TFT/LCD, the number of voltage
sources is M/2 (2 to the (N-1)th power).

      Fig. 1 shows one pixel connected to one data line of TFT/LCD
array and a part of data-drivers connected to one data line and
reference voltage sources.

      Fig. 2 shows a driving scheme of this method.  Tg is a gate
pulse width. Vd is a dataline voltage.  Vs is a voltage of a source
of the TFT.  Vo is an analog multiplexer output connected to the
dataline.

      In the first period of the gate pulse (Tg1), the reference
voltage source No.i supplies the voltage Vi1 required to display gray
level No.(2i-1). In the second period of the gate pulse (Tg2), the
reference voltage source No.i change to the voltage Vi2 required
display gray level No.2i (i=1....