Half tone liquid crystal display circuit with an A.C. voltage divider for drivers

• US 5,250,937 A
• Filed: 03/08/1991
• Issued: 10/05/1993
• Est. Priority Date: 03/08/1990
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Kohji, Konishi, Nobutake, Kikuo, Ono, Tanaka, Takeshi, Ohwada, Jun-ichi
• Primary Examiner(s): BRIER, JEFFERY A
• Application Number:
  US07/666,900
• Time in Patent Office: 942 Days
• Field of Search: 340/784, 340/811, 340/765, 340/793
• US Class Current: 345/89
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• 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 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 2320/028 by changing the viewing angle properties, e.g. widening the viewing angle, adapting the viewing angle to the view direction
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/08 Fault-tolerant or redundant circuits, or circuits in which repair of defects is prepared
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• 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
• CPC Class Codes: G09G 3/3688 suitable for active matrices only
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A half tone liquid crystal display circuit is disclosed including a voltage divider using as a reference voltage a voltage which is approximately determined on the basis of a point of intersection of the extensions of straight lines along the gradients of brightness-voltage characteristics corresponding to at least two observation angles vertically different with respect to a liquid crystal display panel having a TFT active matrix structure to generate driving voltages for the half tone displays associated with a voltage varied to correspond to the observation angles; and a correcting voltage waveform generator for generating a dynamic observation angle correcting voltage varied in association with a vertical scanning operation corresponding to the difference in the vertical observation angles of a liquid crystal display frame. The half tone driving voltages generated by the voltage divider from the dynamic observation angle correcting voltage are subjected to level modulations.

Claims

1. An observation angle correcting method in the half tone display of a liquid crystal, comprising the steps of:

generating an approximate reference voltage from a voltage which is approximately determined on the basis of a point of intersection of the extensions of straight lines along the gradients of brightness-voltage characteristics corresponding to at least two observation angles vertically different with respect to a liquid crystal display panel;

generating a voltage which is varied to correspond to said observation angles; and

generating driving voltages for the half tone displays, which are corrected by a divided voltage associated with said voltage.

15. A driving voltage generator according to claim 1, wherein said voltage dividing circuit is fed through a buffer amplifier of low output impedance with the operating voltage which have been subjected to the observation angle correction and the temperature compensation.

2. A half tone liquid crystal display circuit characterized:

in that an approximate reference voltage is generated from a voltage which is approximately determined on the basis of a point of intersection of the extensions of straight lines along the gradients of brightness-voltage characteristics corresponding to at least two observation angles vertically different with respect to a liquid crystal display panel;

in that a voltage varied to correspond to said observation angles is generated; and

in that driving voltages for the half tone display are generated by a divided voltage associated with said voltage.

3. A half tone liquid crystal display circuit according to claim 2, wherein the driving voltages corresponding to maximum and minimum brightnesses for said half tone displays are independent of said divided voltage.

4. A half tone liquid crystal display circuit according to claim 2, wherein said driving voltages are fed to signal line electrodes to be connected with the drains of the TFT transistors.

5. A half tone liquid crystal display circuit according to claim 2, wherein said reference voltage is made adjustable.

6. A half tone liquid crystal display circuit according to claim 5, wherein the adjustable reference voltage is automatically varied by the output of a temperature compensator.

7. A half tone liquid crystal display circuit according to claim 2, wherein said divided voltage is generated on the basis of resistance elements connected in series.

8. A half tone liquid crystal display circuit according to claim 2, wherein the liquid crystal display panel having said TFT active matrix structure is enabled to perform multi-color display by providing color filters.

9. A half tone liquid crystal display circuit according to claim 2, wherein said half tone liquid crystal display circuit is used as a monitor for an electronic device packaging a microcomputer.

10. A half tone liquid crystal display circuit according to claim 2, further comprising a packaging substrate mounting thereon a voltage source circuit for generating the half tone driving voltages and being so arranged on the back of the liquid crystal display panel as to sandwich a back light inbetween.

11. A driving voltage generator for a half tone liquid crystal display circuit, comprising:

a voltage divider for generating driving voltages for the half tone displays associated with a voltage varied to correspond to said observation angles by using as a reference voltage a voltage which is approximately determined on the basis of a point of intersection of the extensions of straight lines along the gradients of brightness-voltage characteristics corresponding to at least two observation angles vertically different with respect to a liquid crystal display panel having a TFT active matrix structure; and

a switch circuit for feeding operating voltages having inverted polarities to a circuit for generating said reference voltage in accordance with a liquid crystal Ac conversion signal and a voltage dividing circuit.

12. A driving voltage generator according to claim 11, wherein the half tone driving voltages generated by said voltage dividing circuit are individually fed to a voltage follower circuit and an inverted amplifier for inverting the phase in response to said output voltage, and wherein the driving voltages having passed through said voltage follower circuit and said inverted amplifier are individually fed to the drivers which are vertically divided to correspond to the alternate signal lines of the liquid crystal.

13. A driving voltage generator according to claim 11, wherein said voltage dividing circuit is composed of two voltage dividers, of which one is fed through said switch circuit with the operating voltage having its polarity inverted in accordance with an AC conversion signal whereas the other is fed with the operating voltage through a polarity inverting amplifier, and wherein the voltage-divided output voltages of said two voltage dividers are individually fed through said voltage follower circuits to the drivers which are vertically divided to correspond to the alternate signals of the liquid crystal panel.

14. A driving voltage generator according to claim 11, wherein said reference voltage is automatically subjected to a temperature compensation by a temperature compensator corresponding to the temperature dependency thereof.

16. A driving voltage generator according to claim 11, wherein the voltage having passed through said switch circuit for generating said liquid crystal AC conversion driving voltage is fed to a level shifter for generating a bilateral level shift voltage matching the effective threshold voltage of the TFT transistor, to generate the maximum driving voltage at an absolute value to be fed to the signal lines of the liquid crystal through said level shifter.

17. A driving voltage generator according to claim 11, wherein the voltage having its polarity switched through the switch circuit, which has its switching controlled by the AC conversion signal of said liquid crystal, is fed to the observation angle correcting or temperature compensation voltage generator, so that the generated voltage is fed through a buffer amplifier of low output impedance to the voltage dividing circuit for generating the half tone driving voltage.

18. A half tone liquid crystal display circuit, comprising:

a voltage divider for using as a reference voltage a voltage which is approximately determined on the basis of a point of intersection of the extensions of straight lines along the gradients of brightness-voltage characteristics corresponding to at least two observation angles vertically different with respect to a liquid crystal display panel having a TFT active matrix structure, to generate driving voltages for the half tone displays associated with a voltage varied to correspond to said observation angles are generated; and

a correcting voltage waveform generator for generating a dynamic observation angle correcting voltage varied in association with a vertical scanning operation corresponding to the difference in the vertical observation angles of a liquid crystal display frame, wherein the half tone driving voltages generated by said voltage divider from said dynamic observation angle correcting voltage are subjected to level modulations.

19. A half tone liquid crystal display circuit according to claim 18, wherein said voltage divider is fed with said dynamic observation angle correction voltages through a coupling capacitor.

20. A half tone liquid crystal display circuit according to claim 18, wherein said correcting voltage waveform generator includes an integrator for receiving a pulse signal generated for each frame.

21. A half tone liquid crystal display circuit according to claim 18, wherein said correcting voltage waveform generator includes:

a counter adapted to be reset for each frame and to receive a clock pulse corresponding to the scanning line selected;

a decoder for converting the counted output of said counter into the observation angle correction voltage signals in a binary form; and

a D/A converter for generating an analog correction voltage waveform in response to the output signal of said decoder.

22. A half tone liquid crystal display device comprising:

a display panel having a first and a second set of lines;

a first driver means for driving said first set of lines;

a second driver means for driving said second set of lines;

a driving voltage generator means for generating a driving voltage for said second driver means; and

wherein

said driving voltage generator means comprises a correction voltage generator means for generating a correction voltage; and

said correction voltage drops after a lapse of time so observation angles of said display panel are dynamically corrected in synchronism with the vertical scanning timing of said display panel.

23. A half tone liquid crystal display device according to claim 22 wherein said driving voltage generator means further comprises:

a first and second voltage varying means and a plurality of resistors; and

wherein,

said plurality of resistors are connected serially between said first and second voltage varying means.

24. A half tone liquid crystal display device according to claim 23 wherein:

said display panel is a thin film transistor display panel;

said first set of lines are gate lines; and

said second set of lines are drain lines.

25. A half tone liquid crystal display device according to claim 24 wherein:

said correction voltage generator means comprises a resistor and a capacitor.

26. A half tone liquid crystal display device according to claim 24 wherein:

a plurality of half tone driving voltages are outputted from nodes of said serially connected plurality of resistors.

27. A half tone liquid crystal display device according to claim 23 wherein:

a plurality of half tone driving voltages are outputted from nodes of said serially connected plurality of resistors.

28. A half liquid crystal display device according to claim 22 wherein:

said display panel is a thin film transistor display panel;

said first set of lines are gate lines; and

said second set of lines are drain lines.

29. A half tone liquid crystal display device according to claim 22 wherein:

said correction voltage generator means comprises a resistor and a capacitor.

30. A half tone liquid crystal display device according to claim 22 wherein:

said correction voltage generator means comprises a resistor, a capacitor and an operational amplifier.