REDUCING POWER CONSUMPTION IN A LIQUID CRYSTAL DISPLAY

• US 20080259017A1
• Filed: 09/14/2007
• Published: 10/23/2008
• Est. Priority Date: 04/18/2007
• Status: Active Grant

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Kutz, Harold, Wright, David, Muriby, Jason, Hancioglu, Erhan
• Granted Patent: US 9,407,257 B2
• Time in Patent Office: Days
• US Class Current: 345/94
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors
• CPC Class Codes: H03K 19/0016 by using a control or a clock signal, e.g. in order to apply power supply
• CPC Class Codes: H03K 19/00369 Modifications for compensating variations of temperature, supply voltage or other physical parameters

Abstract

Embodiments of the invention relate to a method and apparatus to reduce power consumption in a passive matrix LCD driver circuit by using a plurality of drive buffers and active power management of sub-blocks in the passive matrix LCD drive circuit. Each drive buffer may operate in a first phase, which may include a high-drive mode to drive an LCD voltage to a threshold voltage level and a low-drive mode to modify the LCD voltage to approximate an input voltage of the drive buffer, and to maintain a constant LCD voltage level. The low-drive buffer consumes less current than the high-drive buffer, thus reducing power consumption. The drive buffer may also operate in a second phase, also a no-drive mode, in which the drive buffer and the bias voltage generator may be completely turned off, to further reduce power consumption. The drive buffer may be used to drive capacitive loads, as well as partially-resistive loads and inductive loads.

Claims

1. An apparatus, comprising:

a bias voltage generator to generate a plurality of bias voltages; and

a drive buffer to drive a passive liquid crystal display (LCD) pixel or segment from at least one of the bias voltages, wherein the drive buffer actively drives the passive LCD segment or pixel in a first phase, and wherein the drive buffer ceases to drive the passive LCD segment or pixel in a second phase.

2. The apparatus of claim 1, where the drive buffer includes

a first buffer to drive a voltage associated with the passive LCD pixel or segment to a threshold level;

and

a second buffer to modify the voltage associated with the passive LCD pixel or segment to approximate at least one of the bias voltages, and to compensate a leakage associated with the passive LCD pixel or segment to provide a constant voltage at the passive LCD pixel or segment.

3. The apparatus of claim 2, includes a control circuit having a control signal generator to generate one or more control signals to select between the first buffer and the second buffer.

4. The apparatus of claim 2, where the driver buffer actively drives the passive LCD segment or pixel in the first phase comprises driving the voltage associated with the passive LCD pixel or segment to a threshold voltage level in a high-drive mode.

5. The apparatus of claim 2, where the drive buffer actively drives the passive LCD segment or pixel comprises adjusting the voltage associated with the passive LCD pixel or segment to approximate at least one of the bias voltages, and compensating a leakage associated with the passive LCD pixel or segment to provide a constant voltage at the passive LCD pixel or segment in a low-drive mode.

6. The apparatus of claim 4, where the first buffer is activated during the high-drive mode.

7. The apparatus of claim 5, where the second buffer is activated during the low-drive mode.

8. The apparatus of claim 2, where the drive buffer ceases to drive the passive LCD segment or pixel in the second phase comprises ceasing to drive the passive LCD segment or pixel in a no-drive mode when the voltage associated with the passive LCD pixel or segment reaches a desired voltage level.

9. The apparatus of claim 2, where the second buffer uses an offset cancellation technique.

10. The apparatus of claim 8, where at least one of the bias voltage generator or the drive buffer is turned off during the no-drive mode.

11. A method, comprising:

generating an input voltage;

actively driving a voltage associated with a passive liquid crystal display (LCD) segment or pixel to a threshold level in a first phase;

modifying the voltage associated with the passive LCD segment or pixel to approximate the input voltage in the first phase;

compensating a leakage associated with the passive LCD segment or pixel to maintain the voltage associated with the passive LCD segment or pixel at a substantially constant level in the first phase; and

ceasing to drive the passive LCD segment or pixel associated with the passive LCD segment or pixel in a second phase.

12. The method of claim 11, includes ceasing to drive the passive LCD segment or pixel after the voltage associated with the passive LCD segment or pixel reaches a desired level in a no-drive mode during the second phase.

13. The method of claim 12, includes actively driving the passive LCD segment or pixel in one of a high-drive mode or a low-drive mode during the first phase.

14. The method of claim 13, includes generating one or more control signals to select one of the high-drive mode, the low-drive mode, or the no-drive mode.

15. The method of claim 13, includes canceling a voltage offset using an amplifier with chopper offset cancellation in the low-drive mode.

16. The method of claim 12, includes turning off at least one of the bias voltage generator and the drive buffer in the no-drive mode.

17. An apparatus, comprising:

means for generating an input voltage;

means for actively driving a voltage associated with a passive liquid crystal display (LCD) segment or pixel to a threshold level in a first phase;

means for modifying the voltage associated with the passive LCD segment or pixel to approximate the input voltage in the first phase;

means for compensating a leakage associated with the passive LCD segment or pixel to maintain the voltage associated with the passive LCD segment or pixel at a substantially constant level in the first phase; and

means for ceasing to drive the passive LCD segment or pixel in a second phase.

18. The apparatus of claim 17, include means for ceasing to drive the passive LCD segment or pixel in a no-drive mode during the second phase after the voltage associated with the passive LCD segment or pixel reaches a desired level.

19. The apparatus of claim 18, includes means for actively driving the passive LCD segment or pixel in one of a high-drive mode or a low-drive mode during the first phase.

20. The apparatus of claim 19, includes means for selecting one of the high-drive mode, the low-drive mode, or the no-drive mode.