Display driver

• US 9,626,916 B2
• Filed: 05/13/2014
• Issued: 04/18/2017
• Est. Priority Date: 11/21/2006
• Status: Active Grant

• Current Assignee: Synaptics Japan GK (Synaptics Incorporated)
• Original Assignee: Synaptics Japan GK (Synaptics Incorporated)
• Inventors: Takada, Naoki, Kudo, Yasuyuki, Kurokawa, Yoshiki, Sakamaki, Goro
• Primary Examiner(s): EURICE, MICHAEL
• Application Number:
  US14/275,955
• Publication Number:
  US 20140247291A1
• Time in Patent Office: 1,071 Days
• Field of Search: 345 77, 345 98, 345102, 345204, 348 E512
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 5/10 Intensity circuits

Abstract

In a display driver, a first backlight control unit using a histogram and a second backlight control unit using an optical sensor can be used in combination. The display driver includes a PWM generating unit setting a control signal value consisting of a product of a luminance rate of X % and a luminance rate of Y % as a luminance rate of a control signal for controlling a backlight with respect to maximum backlight luminance when a luminance rate of a control signal obtained by first backlight control with respect to the maximum backlight luminance is X % and a luminance rate of a control signal obtained by second backlight control with respect to the maximum backlight luminance is Y %.

Claims

1. A display device, comprising:

a liquid crystal display panel;

a backlight to illuminate the liquid crystal display panel;

a graphic RAM which stores display data including pixel values;

an optical sensor which senses external-light luminance;

a first backlight control unit generating a first backlight control signal indicating a luminance rate of X % based on a histogram generated from the display data for an upper part of a range of allowed values of the pixel values, the luminance rate of X % being defined as a percentage with respect to a maximum backlight luminance, and the upper part including a pixel value corresponding to a brightest pray-scale level of the allowed values;

a second backlight control unit generating a second backlight control signal indicating a luminance rate of Y % based on the external-light luminance, the luminance rate of Y % being defined as a percentage with respect to the maximum backlight luminance; and

a control unit which receives the first backlight control signal and the second backlight control signal and generates a synthesized backlight control signal based on a product of the luminance rate of X % indicated by the first backlight control signal and the luminance rate of Y % indicated by the second backlight control signal, the product being obtained by multiplication of the luminance rate of X % and the luminance rate of Y %,

wherein a luminance of the backlight is controlled in response to the synthesized backlight control signal.

2. The display device according to claim 1, wherein the control unit is a Pulse Width Modulation (PWM) signal generating unit which provides a PWM control signal in response to the synthesized backlight control signal,

wherein the backlight receives the PWM control signal to control the luminance of the backlight.

3. The display device according to claim 1, wherein the control unit selects a selected luminance rate from the luminance rate of X % and an alternative luminance rate of 100% in response to the luminance rate of Y % calculated by the second backlight control unit in an operation of the second backlight control unit, and calculates the synthesized backlight control signal based on a product of the selected luminance rate and the luminance rate of Y %.

4. The display device according to claim 3, wherein the luminance rate of X % is set to 100% when the luminance rate of Y % is calculated in the operation of the second backlight control unit as being lower than a threshold setting value.