LIGHT SENSING CIRCUIT, LIQUID CRYSTAL DISPLAY HAVING THE SAME, AND METHOD OF DRIVING THE SAME

• US 20100045908A1
• Filed: 01/22/2009
• Published: 02/25/2010
• Est. Priority Date: 08/20/2008
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: WOO, Doo-Hyung
• Granted Patent: US 8,174,486 B2
• Time in Patent Office: Days
• US Class Current: 349/116
• CPC Class Codes: G01J 1/1626 Arrangements with two photodetectors, the signals of which are compared
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266
• CPC Class Codes: G01J 1/4228 arrangements with two or more detectors, e.g. for sensitivity compensation
• CPC Class Codes: G02F 1/13318 Circuits comprising a photodetector
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A light sensing circuit includes a sensor unit, a voltage generator and a readout circuit. The sensor unit includes a first sensor that detects an external light to output a first current value, a third sensor that detects an internal light generated from the backlight unit to output a third current value, and a second sensor that detects a peripheral light isolated from the external light and the internal light to output a second current value. The sensor unit outputs a first differential value between the third current value and the second current value and a second differential value between the first current value and the second current value. The voltage generator generates a reference voltage based on the first differential value and a sensing voltage based on the second differential value. The readout circuit outputs brightness information of the external light using the reference voltage and the sensing voltage.

Claims

1. A light sensing circuit for a liquid crystal display having a backlight unit, the light sensing circuit comprising:

a sensor unit comprising;

a first sensor that detects an external light to output a first current value;

a third sensor that detects an internal light generated from the backlight unit to output a third current value; and

a second sensor that detects a peripheral light isolated from the external light and the internal light to output a second current value,

wherein the sensor unit outputs a first differential value between the third current value and the second current value and a second differential value between the first current value and the second current value;

a voltage generator generating a reference voltage in response to the first differential value and generating a sensing voltage in response to the second differential value; and

a readout circuit generating brightness information of the external light using the reference voltage and the sensing voltage.

2. The light sensing circuit of claim 1, wherein the second and third sensors are serially connected between a first voltage and a second voltage lower than the first voltage to comprise a first subtraction circuit that outputs the first differential value, and the second and first sensors are serially connected between the first voltage and the second voltage to comprise a second subtraction circuit that outputs the second differential value.

3. The light sensing circuit of claim 2, wherein the first to third sensors comprise photodiodes.

4. The light sensing circuit of claim 1, wherein the voltage generator comprises:

an operational amplifier comprising an input terminal receiving the first and second differential values, and an output terminal outputting the reference voltage by integrating the first differential value and outputting the sensing voltage by integrating the second differential value; and

a capacitor connected between the input terminal and the output terminal of the operational amplifier to feedback the reference voltage and the sensing voltage to the input terminal.

5. The light sensing circuit of claim 1, wherein the readout circuit generates the brightness information by detecting a first rising time, during which the reference voltage reaches a predetermined target voltage, and a second rising time, during which the sensing voltage reaches the predetermined target voltage, based on the first rising time, and outputting the second rising time as the brightness information of the external light.

6. The light sensing circuit of claim 5, wherein the readout circuit comprises:

a comparator comparing the sensing voltage with the reference voltage to output an enable signal maintained in a high state when the second rising time of the sensing voltage is shorter than the first rising time of the reference voltage and maintained in a low state when the second rising time of the sensing voltage is longer than the first rising time of the reference voltage; and

a counter receiving the enable signal and counting a number of reference clocks while the enable signal is being maintained in the high state to output the number of reference clocks as digital data.

7. The light sensing circuit of claim 6, wherein the counter stops the counting when the enable signal is maintained in the low state.

8. The light sensing circuit of claim 6, wherein the counter receives the reference voltage from the voltage generator, counts the first rising time of the reference voltage, and outputs a count result as digital control data.

9. The light sensing circuit of claim 8, wherein the readout circuit further comprises:

a memory storing the digital reference data; and

a digital/analog converter receiving the digital reference data from the memory to convert the digital reference data into the reference voltage.

10. The light sensing circuit of claim 8, wherein the digital/analog converter supplies the reference voltage to an input terminal of the comparator.

11. A liquid crystal display comprising:

a liquid crystal display panel comprising a display area displaying an image using a backlight;

a light sensing circuit detecting brightness information of an external light incident into the liquid crystal display panel; and

a backlight unit supplying the backlight to the liquid crystal display panel and controlling a brightness of the backlight based on the brightness information,

wherein the light sensing circuit comprises;

a first sensor that detects the external light to output a first current value, a third sensor that detects the backlight to output a third current value, and a second sensor that detects a peripheral light isolated from the external light and the backlight to output a second current value, the sensor unit outputting a first differential value between the third current value and the second current value and a second differential value between the first current value and the second current value;

a voltage generator generating a reference voltage in response to the first differential value and generating a sensing voltage in response to the second differential value; and

a readout circuit detecting a first rising time, during which the reference voltage reaches a predetermined target voltage, and a second rising time, during which the sensing voltage reaches the predetermined target voltage, based on the first rising time, and outputting the second rising time as brightness information of the external light.

12. The liquid crystal display of claim 11, wherein the liquid crystal display panel further comprises a peripheral area surrounding the display area and the light sensing circuit is disposed on the peripheral area.

13. The liquid crystal display of claim 12, wherein the light sensing circuit is integrated on the peripheral area through a thin film process.

14. The liquid crystal display of claim 11, wherein the voltage generator comprises:

an operational amplifier comprising an input terminal receiving the first and second differential values, and an output terminal outputting the reference voltage by integrating the first differential value and outputting the sensing voltage by integrating the second differential value; and

a capacitor connected between the input terminal and the output terminal of the operational amplifier to feedback the reference voltage and the sensing voltage to the input terminal.

15. The liquid crystal display of claim 11, wherein the readout circuit comprises:

a comparator comparing the sensing voltage with the reference voltage to output an enable signal maintained in a high state when the second rising time of the sensing voltage is shorter than the first rising time of the reference voltage and maintained in a low state when the second rising time of the sensing voltage is longer than the first rising time of the reference voltage; and

a counter receiving the enable signal and counting a number of reference clocks while the enable signal is being maintained in the high state to output the number of reference clocks as digital data.

16. The liquid crystal display of claim 11, wherein the liquid crystal display panel comprises:

an array substrate;

an opposite substrate facing the array substrate;

a liquid crystal layer interposed between the array substrate and the opposite substrate;

a first light blocking layer disposed on the array substrate and configured to prevent backlight from being introduced into the first sensor and the second sensor;

a second light blocking disposed on the opposite substrate and configured to prevent the external light from being introduced into the second sensor and the third sensor.

17. The liquid crystal display of claim 16, wherein the first light blocking surrounds the display area.

18. The liquid crystal display of claim 16, wherein the first light blocking layer overlaps the first sensor and the second sensor, and the second light blocking layer overlaps the second sensor and the third sensor.

19. A method of driving a light sensing circuit that detects brightness information of an external light, the method comprising:

detecting an external light and outputting a first current value that is representative of the external light, detecting an internal light generated by a backlight and outputting a third current value that is representative of the internal light, and detecting a peripheral light isolated from the external light and the internal light and outputting a second current value that is representative of the peripheral light;

detecting a first differential value between the third current value and the second current value and a second differential value between the first current value and the second current value;

generating a reference voltage by integrating the first differential value;

generating a sensing voltage by integrating the second differential value;

converting the sensing voltage into digital data based on a first time during which the reference voltage reaches a predetermined target voltage; and

detecting the brightness information of the external light based on the digital data.

20. The method of claim 19, wherein the converting of the sensing voltage into the digital data comprises:

counting the first time and converting a count result thereof into first data;

counting a second time during which the sensing voltage reaches the predetermined target voltage and converting a count result thereof into second data; and

converting the second data into the digital data based on the first time included in the first data.