Liquid crystal display device, driving circuit, driving method, and electronic apparatus

• US 6,778,163 B2
• Filed: 12/20/2001
• Issued: 08/17/2004
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: 138 East LCD Advancements Limited (Vector Capital Corporation)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Ozawa, Tokuro
• Primary Examiner(s): Shankar, Vijay
• Assistant Examiner(s): Patel, Nitin
• Application Number:
  US10/022,616
• Publication Number:
  US 20020084970A1
• Time in Patent Office: 971 Days
• Field of Search: 345/87, 345/89, 345/690, 345/100, 345/209, 345/98, 345/96, 345/90
• US Class Current: 345/96
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• 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 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/023 using energy recovery or conservation
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

The present invention provides a liquid crystal display in which a voltage amplitude of a data signal which is supplied to a data line, is kept small, thereby reducing the power consumption. When a scanning signal supplied to a scanning line is set to an H level, a data signal with the voltage depending on the gray level and depending on the writing polarity is applied to a data line. In this case, a thin-film transistor (TFT) is turned on, thus a liquid crystal capacitor and storage capacitor store the charge corresponding to the data signal. Then, the scanning signal is set to an L level to turn TFT off, and the voltage of the other terminal of the storage capacitor is raised from the low side of capacitor voltage V_st(−) to the high side V_st((+)), and the charge corresponding to the raised voltage amount is redistributed to the liquid crystal capacitor. By this means, the effective voltage value applied to the liquid crystal capacitor can correspond to the voltage amplitude of the data signal or more. Accordingly, the present invention can reduce the voltage amplitude of the voltage signal applied to the data line in comparison with the voltage amplitude applied to a pixel electrode, therefore allowing power consumption to be reduced.

Claims

1. A liquid crystal display device, comprising:

a scanning line to which an on-voltage is applied and then an off-voltage is applied;

a liquid crystal capacitor having a liquid crystal sandwiched between a counter electrode and a pixel electrode;

a D/A converter that applies a voltage, which corresponds to gray scale data indicating a gray level and to a writing polarity of a voltage applied to said liquid crystal, the voltage being applied to a data line when an on-voltage is applied to said scanning line;

a switching element disposed between said data line and said pixel electrode, said switching element being turned on when the on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied; and

a storage capacitor having first terminal connected to said pixel electrode and second terminal, wherein, when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of positive-polarity writing, the voltage of second terminal is shifted to a high level when the off-voltage is applied to said scanning line, and when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of negative-polarity writing, the voltage of the second terminal is shifted to a low level when the off-voltage is applied to said scanning line the voltage applied to the second terminal when the on-voltage is applied to the scanning line being different from the voltage applied to the second terminal when the off-voltage is applied to the scanning line.

2. A liquid crystal display device according to claim 1, the other terminal of said storage capacitor being connected to each row in common via a capacitor line.

3. An electronic apparatus comprising a liquid crystal display device according to claim 1.

4. A liquid crystal display device, comprising:

a scanning line to which an on-voltage is applied and then an off-voltage is applied;

a liquid crystal capacitor having a liquid crystal sandwiched between a counter electrode and a pixel electrode;

a D/A converter that applies a voltage, which corresponds to gray scale data indicating a gray level and to a writing polarity of a voltage applied to said liquid crystal, the voltage being applied to a data line when an on-voltage is applied to said scanning line;

a switching element disposed between said data line and said pixel electrode, said switching element being turned on when the on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied; and

a storage capacitor having one terminal connected to said pixel electrode, wherein, when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of positive-polarity writing, the voltage of another terminal is shifted to a high level when the off-voltage is applied to said scanning line, and when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of negative-polarity writing, the voltage of the other terminal is shifted to a low level when the off-voltage is applied to said scanning line, wherein in the case where said writing polarity of a voltage applied to said liquid crystal is one of positive-polarity and negative-polarity, the display device further comprises;

a first power feeding line which is fed with a first voltage during a preset period, and which is fed with a second voltage which is higher than said first voltage during a set period after said preset period;

a second power feeding line which is fed with a third voltage which is higher than said second voltage during said preset period, and which is fed with a fourth voltage which is lower than said third voltage and higher than said second voltage during said set period after said preset period; and

a selector that selects one of said first and second power feeding lines during said preset period, and that selects the other one of said first and second power feeding lines during said set period, wherein said D/A converter generates a supply voltage to said data line using the corresponding voltage selected by said selector during said preset period and said set period.

5. A liquid crystal display device according to claim 4, wherein in the case where said writing polarity of a voltage applied to said liquid crystal is the other one of positive-polarity and negative-polarity,

the first power feeding line is fed with a fifth voltage during the preset period, and is fed with a sixth voltage which is higher than said fifth voltage during the set period after said preset period, whereas

the second power feeding line is fed with a seventh voltage which is higher than said sixth voltage during said preset period, and is fed with an eighth voltage which is lower than said seventh voltage and higher than said sixth voltage during said set period.

6. A liquid crystal display device, comprising:

a scanning line to which an on-voltage is applied and then an off-voltage is applied;

a liquid crystal capacitor having a liquid crystal sandwiched between a counter electrode and a pixel electrode;

a D/A converter that applies a voltage, which corresponds to gray scale date indicating a gray level and to a writing polarity of a voltage applied to said liquid crystal, the voltage being applied to a data line when an on-voltage is applied to said scanning line;

a switching element disposed between said data line and said pixel electrode, said switching element being turned on when the on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied; and

a storage capacitor having one terminal connected to said pixel electrode, wherein, when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of positive-polarity writing, the voltage of another terminal is shifted to a high level when the off-voltage is applied to said scanning line, and when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of negative-polarity writing, the voltage of the other terminal is shifted to a low level when the off-voltage is applied to said scanning line, wherein said D/A converter includes, in the case where said writing polarity of a voltage applied to said liquid crystal is one of positive-polarity and negative-polarity;

a first switch that applies one of a first or third voltage to said data line corresponding to upper bits of said gray scale data during a preset period; and

a capacitor having a capacitance corresponding to the lower bits excluding the upper bits from said gray scale data, wherein, in the case where said first voltage is applied to said data line, a fourth voltage which is higher than said first voltage is applied to one terminal, whereas, in the case where said third voltage is applied to said data line, a second voltage which is higher than said third voltage is applied to one terminal, and another terminal is connected to said data line during a set period after said preset period.

7. A liquid crystal display device according to claim 6, capacitor further comprising a bit capacitor corresponding to weighting of said lower bits, and a second switch which is arranged corresponding to said bit capacitor, and which is turned on or off depending on said lower bits.

8. A liquid crystal display device according to claim 6, further comprising:

a first power feeding line which is fed with said first voltage during said preset period, and which is fed with said second voltage during said set period after the preset period;

a second power feeding line which is fed with said third voltage during said preset period, and which is fed with said fourth voltage during said set period; and

a selector which selects either one of said first power feeding line or said second power feeding line based on said upper bits, and that supplies the voltage which is fed to the selected power feeding line to the input terminal of said first switch during said preset period, and which selects the other one of said first power feeding line or said second power feeding line during said preset period, and feeds the voltage which is fed to the selected power feeding line to one terminal of said capacitor.

9. A liquid crystal display device according to claim 6, wherein, in the case where said writing polarity of a voltage applied to said liquid crystal is the other one of positive-polarity and negative-polarity;

said first switch supplies one of a fifth voltage or a seventh voltage to said data line based on the upper bits of said gray scale data during the preset period, and

one terminal of said capacitor is supplied with an eighth voltage which is higher than said fifth voltage in the case where said data line is supplied with said fifth voltage, whereas seventh voltage in the case where said data line is supplied with said seventh voltage.

10. A liquid crystal display device according to claim 9, wherein a first power feeding line is fed with a fifth voltage during the preset period, and is fed with a sixth voltage during said set period after the preset period, whereas

a second power feeding line is fed with the seventh voltage during said preset period, and being fed with the eighth voltage during said set period.

11. A liquid crystal display device, comprising:

a scanning line to which an on-voltage is applied and then an off-voltage is applied;

a liquid crystal capacitor having a liquid crystal sandwiched between a counter electrode and a pixel electrode;

a D/A converter that applies a voltage, which corresponds to gray scale data indicating a gray level and to a writing polarity of a voltage applied to said liquid crystal, the voltage being applied to a data line when an on-voltage is applied to said scanning line;

a switching element disposed between said data line and said pixel electrode, said switching element being turned on when the on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied; and

a storage capacitor having one terminal connected to said pixel electrode, wherein, when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of positive-polarity writing, the voltage of another terminal is shifted to a high level when the off-voltage is applied to said scanning line, and when the writing polarity of a voltage applied to said liquid crystal during a period in which the on-voltage is applied to said scanning line is equivalent to that of negative-polarity writing, the voltage of the other terminal is shifted to a low level when the off-voltage is applied to said scanning line, the ration of the capacitance of said storage capacitor to said liquid crystal capacitor being four or greater.

12. A driving circuit for a liquid crystal display device, including a liquid crystal capacitor arranged at a intersection of a scanning line and a data line, and having a liquid crystal sandwiched between a counter electrode and pixel electrode, a switching element inserted between said data line and said pixel electrode, said switching element being turned on when an on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied to said scanning line, and a capacitor having first terminal connected to said pixel electrode and second terminal, the driving circuit comprising:

a scanning line driving circuit that applies said on-voltage to said scanning line, and then applies said off-voltage to said scanning line;

a D/A converter that applies a voltage corresponding to gray scale data indicating a gray level, and corresponding to a writing polarity of a voltage applied to said liquid crystal, to a data line when said scanning line driving circuit applies the on-voltage to said scanning line; and

a storage capacitor driving circuit wherein, when, in the case of applying the on- voltage to said scanning line, the voltage applied to said data line is equivalent to that of positive-polarity writing, then the voltage of the second terminal is shifted to high when the off-voltage is applied to said scanning line, and when in the case of applying the on-negative-polarity writing when the off-voltage is applied to said scanning line, then the voltage of the second terminal of said storage capacitor is shifted to low, the voltage applied to the second terminal when the on-voltage is applied to the scanning line being different from the voltage applied to the second terminal when the off-voltage is applied to the scanning line.

13. A driving method for a liquid crystal display device having a liquid crystal capacitor disposed at the intersection of a scanning line and a data line, and further having a liquid crystal sandwiched between a counter electrode and a pixel electrode, a switching element inserted between said data line and said pixel electrode, said switching element being turned on when an on-voltage is applied to said scanning line, and being turned off when an off-voltage is applied to said scanning line, and a storage capacitor having first terminal connected to said pixel electrode and second terminal, the driving method comprising:

applying an on-voltage to said scanning line;

applying a voltage corresponding to gray scale data indicating a gray level, and corresponding to a writing polarity of a voltage applied to said liquid crystal, to a data line;

applying off-voltage to said scanning line;

if the writing polarity of a voltage applied to said liquid crystal to said data line is equivalent to that of positive-polarity writing, shifting the voltage of second terminal to high; and

if the writing polarity of a voltage applied to said liquid crystal to said scanning line is equivalent to that of negative-polarity writing, shifting the voltage of the second terminal of said storage capacitor to low when the off-voltage is applied to said scanning line, the voltage applied to the second terminal when the on-voltage is applied to the scanning line being different from the voltage applied to the second terminal when the off-voltage is applied to the scanning line.