Liquid-crystal panel driving device, and liquid-crystal apparatus

• US 6,600,470 B1
• Filed: 09/10/1999
• Issued: 07/29/2003
• Est. Priority Date: 09/11/1998
• Status: Expired due to Term

• Current Assignee: BOE Technology Group Co., Ltd.
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Tsuda, Atsunari
• Primary Examiner(s): Chow, Dennis-Doon
• Application Number:
  US09/394,528
• Time in Patent Office: 1,418 Days
• Field of Search: 345/89, 345/119, 345/87, 349/162
• US Class Current: 345/89
• 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 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/04 Maintaining the quality of display appearance
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/367 with a nonlinear element in series with the liquid crystal cell, e.g. a diode, or M.I.M. element
• CPC Class Codes: G09G 3/3685 Details of drivers for data electrodes

Abstract

The invention relates to driving a transflective liquid-cystal panel in such a manner as to increase a contrast ratio during a transmissive-type display time while appropriately maintaining the brightness during a reflective-type display. The liquidcrystal panel includes a Y driver circuit and an X driver circuit for supplying an applied voltage having an effective value of a magnitude corresponding to the gray scale level indicated by gray scale data to a liquid crystal element, and a driver control circuit for switching the setting of each magnitude of an effective value of an applied voltage with respect to each gray scale level in the X driver circuit to a setting for a reflective-type display in response to the non-switching on of a light source and to a setting for a transmissive-type display in response to the switching on of the light source.

Claims

1. A liquid-crystal panel driving device for driving a transflective type liquid-crystal panel, the liquid-crystal panel comprising:

a liquid-crystal element having a liquid crystal held between a pair of substrates and in which an alignment state of the liquid crystal can be varied according to the effective value of an applied voltage applied to the liquid crystal;

a pair of polarized-light separation devices disposed with the liquid-crystal element interposed therebetween;

a light source that causes light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display being produced by reflecting external light via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display being produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light sources is switched on;

the liquid-crystal panel driving device comprising;

a supply device that supplies to the liquid-crystal element the applied voltage having an effective value of magnitude corresponding to the magnitude of a gray scale level indicated by gray scale data;

a switch that switches a setting of each magnitude of the effective value with respect to each gray scale level in the power supply device to a setting for the reflective-type display in response to the non-switching on of the light source and for switching to a setting for the transmissive-type display in response to the switching on of the light source; and

a driver that sets the effective value of the voltage to a value so as to permit one of a contrast ratio and brightness that the liquid-crystal panel displays as a reflective-type and one of a contrast ratio and brightness that the liquid-crystal panel displays as a transmissive-type to be similar to each other, respectively.

2. The liquid-crystal panel driving device according to claim 1, the liquid-crystal element further comprising:

a plurality of data lines, disposed on the substrate, to which a data signal is supplied; and

a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data lines and the scanning lines, respectively.

3. The liquid-crystal panel driving device according to claim 1, the supply device further comprising:

a data-signal supply device that supplies to the data lines a data signal having a pulse width corresponding to the gray scale level.

4. The liquid-crystal panel driving device according to claim 1, the switch switching a setting of the magnitude of the effective value so that, in the setting for the reflective-type display, a transmittance of an external light in the liquid-crystal device becomes relatively large over an entire region of the gray scale level, and that in the setting for the transmissive-type display, a transmittance of the light-source light in the liquid-crystal device becomes relatively small over the entire region of the gray scale level.

5. The liquid-crystal panel driving device according to claim 1, the switch switching a setting of the magnitude of the effective value so that, in the setting for the reflective-type display, a variation of a transmittance of an external light in the liquid-crystal device with respect to a variation of the gray scale level becomes relatively small, and that in the setting for the transmissive-type display, a variation of a transmittance of the light-source light with respect to the variation of the gray scale level in the liquid-crystal device becomes relatively large.

6. The liquid-crystal panel driving device according to claim 1, further comprising:

a switching-on control device that controls switching on and non-switching on of the light source, the switch switching a setting of a magnitude of the effective value in synchronization with the control of switching on and non-switching on by the switching-on control device.

7. A liquid-crystal device comprising:

the liquid-crystal panel driving device according to claim 1; and

a liquid-crystal panel.

8. The liquid-crystal device according to claim 7, the liquid-crystal element comprising:

a plurality of data lines, disposed on the substrate, to which a data signal is supplied;

a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied; and

a plurality of two-terminal-type nonlinear elements, which are connected in series, respectively, together with a liquid-crystal portion in each pixel, between the plurality of data lines and the plurality of scanning lines.

9. The liquid-crystal device according to claim 8, the two-terminal-type nonlinear element comprising a TFD (Thin Film Diode) driving element.

10. The liquid-crystal device according to claim 7, the pair of polarized-light separation devices being formed of a pair of polarizers disposed so as for their transmission axes to form a predetermined angle.

11. The liquid-crystal device according to claim 10, the liquid-crystal panel further comprising:

a transflector disposed on a side opposite to the liquid-crystal element with respect to one of the pair of polarizers.

12. The liquid-crystal device according to claim 11, the light source causing the light-source light to enter the liquid-crystal element via the transflector and the one polarizer of the pair of polarizers.

13. A liquid-crystal panel driving device for driving a transflective type liquid-crystal panel, the liquid-crystal panel comprising:

a liquid-crystal element having a liquid crystal held between a pair of substrates and in which an alignment state of the liquid crystal can be varied according to the effective value of an applied voltage applied to the liquid crystal;

a pair of polarized-light separation devices disposed with the liquid-crystal element interposed therebetween;

a light source that causes light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display being produced by reflecting external light via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display being produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light source is switched on;

the liquid-crystal panel driving device comprising;

a supply device that supplies to the liquid-crystal element the applied voltage having an effective value of a magnitude corresponding to the magnitude of a gray scale level indicated by gray scale data; and

a switch that switches a setting of each magnitude of the effective value with respect to each gray scale level in the power supply device to a setting for the reflective-type display in response to the non-switching on of the light source and for switching to a setting for the transmissive-type display in response to the switching on of the light source;

the liquid-crystal element further comprising;

a plurality of data lines, disposed on the substrate, to which a data signal is supplied; and

a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data lines and the scanning lines, respectively;

the supply device further comprising;

a data-signal supply device that supplies to the data lines a data signal having a pulse width corresponding to the gray scale level;

the switch switching the setting of each pulse width of the data signal with respect to each gray scale level in the data-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source, thereby switching the setting of each magnitude of the effective value.

14. The liquid-crystal panel driving device according to claim 13, the switch further comprising:

a first pulse generator that generates a first pulse signal for gray scale control, formed of a plurality of pulses, arranged in such a manner as to correspond to intervals of the gray scale level which is a reference for the setting of the pulse width for the reflective-type display;

a second pulse generator that generates a second pulse signal for gray scale control, formed of a plurality of pulses, arranged in such a manner as to correspond to the intervals of the gray scale level which is a reference for the setting of the pulse width for the transmissive-type display; and

a pulse signal switch that selectively supplies the first pulse signal for gray scale control to the data-signal supply device in response to the non-switching on of the light source and that selectively supplies the second pulse signal for gray scale control in response to the switching on of the light source to the data-signal supply device.

15. A liquid-crystal panel driving device for driving a transflective type liquid-crystal panel, the liquid-crystal panel comprising:

a liquid-crystal element having a liquid crystal held between a pair of substrates and in which an alignment state of the liquid crystal can be varied according to the effective value of an applied voltage applied to the liquid crystal;

a pair of polarized-light separation devices disposed with the liquid-crystal element interposed therebetween;

a light source that causes light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display being produced by reflecting external light via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display being produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light source is switched on;

the liquid-crystal panel driving device comprising;

a supply device that supplies to the liquid-crystal element the applied voltage having an effective value of a magnitude corresponding to the magnitude of a gray scale level indicated by gray scale data; and

a switch that switches a setting of each magnitude of the effective value with respect to each gray scale level in the power supply device to a setting for the reflective-type display in response to the non-switching on of the light source and for switching to a setting for the transmissive-type display in response to the switching on of the light source;

the liquid-crystal element further comprising;

a plurality of data lines, disposed on the substrate, to which a data signal is supplied; and

a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data lines and the scanning lines, respectively;

the supply device further comprising;

a data-signal supply device that supplies to the data lines a data signal having a pulse width corresponding to the gray scale level;

the switch switching the setting of each pulse width of the data signal with respect to each gray scale level in the data-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source, thereby switching the setting of each magnitude of the effective value.

a light source that causes light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display being produced by reflecting external light via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display being produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light source is switched on;

the liquid-crystal panel driving device comprising;

a supply device that supplies to the liquid-crystal element the applied voltage having an effective value of a magnitude corresponding to the magnitude of a gray scale level indicated by gray scale data; and

a switch that switches a setting of each magnitude of the effective value with respect to each gray scale level in the power supply device to a setting for the reflective-type display in response to the non-switching on of the light source and for switching to a setting for the transmissive-type display in response to the switching on of the light source, without inverting the relationship between the gradation level and the transmittance;

the liquid-crystal element further comprising;

a plurality of data lines, disposed on the substrate, to which a data signal is supplied; and

a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data lines and the scanning lines, respectively;

the supply device comprising;

a data-signal supply device that supplies a data signal having a pulse width corresponding to the gray scale level to the data lines; and

a scanning-signal supply device that supplies a scanning signal having a predetermined width to the scanning lines.

16. The liquid-crystal panel driving device according to claim 15, the switch switching a setting of a crest value of the scanning signal in the scanning-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source, thereby switching the setting of each magnitude of the effective value.

17. The liquid-crystal panel driving device according to claim 16, the switch comprising:

a first control voltage supply device that supplies a first control voltage which is a reference for the setting of the crest value for the reflective-type display;

a second control voltage supply device that supplies a second control voltage which is a reference for the setting of the crest value for the transmissive-type display; and

a control voltage switch that selectively supplies the first control voltage to the scanning-signal supply device in response to the non-switching on of the light source and for selectively supplying the second control voltage to the scanning-signal supply device in response to the switching on of the light source.

18. A liquid-crystal panel driving device for driving a liquid-crystal element in a transflective type liquid-crystal panel by supplying thereto a voltage having an effective value corresponding to a gray scale level defined by gray scale data, the liquid-crystal panel driving device comprising:

a driver that sets the effective value of the voltage to a value so as to permit one of a contrast ratio and a brightness that the liquid-crystal panel displays as a reflectivetype and the one of the contrast ratio and brightness that the liquid-crystal panel displays as a transmissive-type to be similar to each other, respectively.

19. A liquid-crystal panel driving device as set forth in claim 18, wherein the driver sets the effective value of the voltage to one of a value so as to permit the contrast ratio displayed in the reflective-type to decrease and a value so as to permit the contrast ratio displayed in the transmissive-type to increase.

20. A liquid-crystal panel driving device as set forth in claim 18, wherein the driver sets the effective value of the voltage to one of a value so as to permit the brightness displayed in the reflective-type to increase and a value so as to permit the brightness displayed in the transmissive-type to decrease.

21. A liquid crystal device comprising:

the liquid-crystal panel driving device according to claims 18; and

a liquid-crystal panel.

22. A liquid-crystal panel driving device for driving a liquid-crystal element in a transflective type liquid-crystal panel by supplying thereto a voltage having an effective value corresponding to a gray scale level defined by gray scale data, the liquid-crystal panel driving device comprising:

a switch that switches a setting of a relationship between a gradation level and a transmittance, which differs for a reflective-type display and a transmissive-type display without inverting the relationship between the gradation level and the transmittance.

23. The liquid-crystal panel driving device according to claim 22, the relationship having the feataure that the trasmittance for the reflective-type display is higher than the transmittance for the transmissive-type display for a same halftone gradation level.

24. A liquid-crystal device comprising:

the liquid-crystal panel driving device according to claim 22; and

a liquid-crystal panel.

25. A liquid-crystal panel driving device for driving a transflective type liquid-drystal panel, the liquid-crystal panel comprising:

a liquid-crystal element having a liquid crystal held between a pair of substrates and in which an alignment state of the liquid crystal can be varied according to the effective value of an applied voltage applied to the liquid crystal;

a pair of polarized-light separation devices disposed with the liquid-crystal element interposed therebetween;

a light source that causes light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display being produced by reflecting external light via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display being produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light sources is switched on;

the liquid-crystal panel driving device comprising;

a supply device that supplies to the liquid-crystal element the applied voltage having an effective value of a magnitude corresponding to the magnitude of a gray scale level indicated by gray scale data;

a first switch that switches a setting of each magnitude of the effective value with respect to each gray scale level in the power supply device to a setting for the reflective-type display in response to the non-switching on of the light source and for switching to a setting for the transmissive-type display in response to the switching on of the light source; and

a second switch that switches a setting of a relationship between a gradation level and a transmittance, which differs for the reflective-type display and the transmissive-type display without inverting the relationship between the gradation level and the transmittance.

26. The liquid-crystal panel driving device according to claim 25, the relationship having the feature that the transmittance for the reflective-type display is higher than the transmittance for the transmissive-type display for a same halftone gradation level.

27. A liquid-crystal device comprising:

the liquid-crystal panel driving device according to claim 25; and

a liquid-crystal panel.