Matrix-addressed liquid crystal display device with compensation for potential shift of pixel electrodes

• US 4,789,223 A
• Filed: 03/27/1986
• Issued: 12/06/1988
• Est. Priority Date: 03/28/1985
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Kasahara, Koichi, Yanagisawa, Toshio, Kajimura, Motoji
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): DUONG, TAI V
• Application Number:
  US06/844,570
• Time in Patent Office: 985 Days
• Field of Search: 350/332, 350/333, 350/350 S, 350/334, 340/784, 340/765, 340/805, 340/811, 340/813-814
• US Class Current: 349/43
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A matrix-addressed liquid crystal display device is constructed of a pair of substrates facing each other with liquid crystal cells arranged in n rows and m columns on one of the substrates. Switches included in each cell comprise field effect transistors with n address lines forming a common connection for the gate electrodes of the field effect transistors in each row and m signal lines forming a common connection for the drain electrode or source electrode of the field effect transistors in each column. A common electrode is arranged on the other substrate and a liquid crystal layer interposed between the substrates. An address line drive circuit supplies a sequential scanning signal to the n address lines; and, a signal line drive circuit supplies a display signal to the m signal lines.

An asymmetrical display signal is selected whereby the voltage applied cross the liquid crystal layer is controlled to be a pure AC signal with no DC component.

Claims

1. A matrix-addressed liquid crystal display device for displaying half-tone pictures comprising:

a pair of substrates facing each other;

switch elements arranged in n rows and m columns on the first of said pair of substrates, each of said switch elements comprising a field effect transistor with a gate, drain and source;

pixel electrodes each connected to said source or drain of each of said field effect transistors;

n address lines forming a common connection for said respective gates of said field effect transistors in each row;

m signal lines forming a common connection for respective drains or sources of said field effect transistors in each column;

a common electrode arranged on the second of said pair of said substrates;

a liquid crystal layer interposed between said substrates, molecules in said liquid crystal layer being arranged in a predetermined alignment, the alignment being changed in accordance with the voltage applied to said liquid crystal layer, and the capacitance between said pixel electrode and said common electrode being changed in relation to said change of the alignment;

an address line drive circuit supplying sequential scanning signals to said n address lines;

a signal line drive circuit supplying parallel display signals to said m signal lines;

polarity inversion circuit means connected to said signal line drive circuit so that said parallel display signals possess a polarity inversion every frame scanning period;

wherein the amplitude of the display signals at one polarity constituting the positive potential side with respect to a polarity inversion reference potential and the amplitude of the display signals at the other polarity constituting the negative potential side are set at different values in order to compensate flor the potential shift of said pixel electrodes;

wherein

the potential shift depends on the ratio of parasitic capacitance, between said gate and said source or drain of said transistor and said liquid crystal layer capacitance, and between said pixel electrode and said common electrode, wherein said liquid crystal layer capacitance varies with the molecule alignment change owing to the display signal voltage applied to said liquid crystal layer.

2. The matrix-addressed liquid crystal display device according to claim 1 wherein said field effect transistors comprise n channel field effect transistors, and the amplitude of said display signal of the one polarity constituting the positive potential side with respect to said polarity inversion reference potential is made smaller than the amplitude of said display signal of the other polarity constituting the negative potential side.

3. The matrix-addressed liquid crystal display device according to claim 1 wherein said n channel field effect transistor are thin film transistors.

4. The matrix-address liquid crystal device according to claim 1 wherein said field effect transistors are comprised of pairs of complementary field effect transistors comprised of n channel and p channel field effect transistors.

5. The matrix-addressed liquid crystal display device according to claim 1 wherein said field effect transistors comprise p channel field effect transistors, and the amplitude of the display signal voltage of the one polarity constituting the positive potential side with respect to said polarity inversion reference potential is made greater than the amplitude of the signal voltage of the other polarity constituting the negative potential side.

6. The matrix-addressed liquid crystal display device according to claim 4 wherein said p channel field effect transistors are thin film transistors.

7. The matrix-addressed liquid crystal display device according to claim 1 wherein the ratio of the display signal amplitudes at each polarity is set so that the voltages applied to the liquid crystal layers have no DC voltage component.

8. The matrix-addressed liquid crystal display device according to claim 5 wherein the ratio of the greater to the lesser of the display signal amplitudes at each polarity is in the range of 1.5 to 3.

9. The matrix-addressed liquid crystal display device according to claim 5 wherein said source or drain is coextensive with the display electrode.