Data line drivers with column initialization transistor

• US 5,686,935 A
• Filed: 03/06/1995
• Issued: 11/11/1997
• Est. Priority Date: 03/06/1995
• Status: Expired due to Fees

• Current Assignee: Thomson Consumer Electronics SA (Vantiva SA)
• Original Assignee: Thomson Consumer Electronics SA (Vantiva SA)
• Inventors: Weisbrod, Sherman
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): LEWIS, DAVID LEE
• Application Number:
  US08/399,012
• Time in Patent Office: 981 Days
• Field of Search: 345/90-93, 345/100, 345/98, 345/104, 345/204
• US Class Current: 345/100
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A video display driver applies a video signal to column electrodes of a liquid crystal display. The display driver includes a reference ramp generator and column data line drivers. A reference ramp signal is combined with the video signal and applied to an input of a comparator. The comparator controls a first transistor that couples a data ramp signal to a given column of pixels. The first transistor at least partially initializes a voltage developed in the given column of pixels prior to an instant when the data ramp signal begins upramping. A second transistor that is coupled in parallel with the first transistor insures that the column voltage is fully initialized.

Claims

1. A data line driver for applying a video signal to a column electrode of a display device, comprising:

a source of said video signal;

a source of a data ramp signal;

a first transistor having a first main current conducting terminal coupled to said source of said data ramp signal and a second main current conducting terminal coupled to said column electrode and responsive to said video signal for applying said data ramp signal to said column electrode during a controllable portion of a period of said data ramp signal that varies in accordance with said video signal to develop a column electrode signal at said column electrode; and

a second transistor responsive to an initialization control signal and coupled to said column electrode for initializing said column electrode signal via a signal path that bypasses said first transistor.

2. A data line driver according to claim 1 wherein a main current conducting current path in said first transistor is coupled in parallel with a main current conducting path of said second transistor.

3. A data line driver according to claim 1 wherein said first transistor at least partially initializes said column electrode signal prior to said controllable portion.

4. A data line driver according to claim 1 wherein, prior to said controllable portion, each of said first and second transistors couples said column electrode to said data ramp signal source for applying an inactive level of said data ramp signal to said column electrode.

5. A data line driver according to claim 4 wherein said first and second transistors apply said inactive level to said column electrode during first and second intervals, respectively, that are at least partially non-overlapping.

6. A data line driver according to claim 1 further comprising, a comparator coupled to a control terminal of said first transistor for controlling said controllable portion, a source of a second control signal coupled to said comparator for calibrating said comparator, said second control signal rendering said first transistor conductive in a manner to provide for at least partial initialization of said column electrode signal.