AMBIENT LIGHT SENSOR WITH INTERNAL LIGHT CANCELLATION

• US 20150122978A1
• Filed: 11/07/2013
• Published: 05/07/2015
• Est. Priority Date: 11/07/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Guillou, Jean-Pierre S., Aflatooni, Koorosh, deJong, Erik G.
• Granted Patent: US 9,612,152 B2
• Time in Patent Office: Days
• US Class Current: 250/225
• CPC Class Codes: G01J 1/0429 using polarisation elements
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266

Abstract

An electronic device includes a transparent surface, a light emitting device that emits light through the transparent surface, and a light sensor for receiving ambient light and providing an ambient light value. A retarder and a linear polarizer are placed between the transparent surface and the light emitting device. The retarder and linear polarizer may attenuate internal reflections from the transparent surface. The light sensor may have two channels and a second linear polarizer may attenuate the ambient light directed toward a second channel. A second retarder may be used with the second linear polarizer to attenuate the ambient light directed toward the second channel. A light detection circuit may use the difference between the two channels of the light sensor to provide the ambient light value.

Claims

1. An electronic device comprising:

a transparent surface;

a light emitting device that emits light through the transparent surface;

a first retarder between the transparent surface and the light emitting device;

a first linear polarizer between the transparent surface and the light emitting device;

a light sensor for receiving ambient light that passes through the first retarder and the first linear polarizer after passing through the transparent surface.

2. The electronic device of claim 1 wherein the first linear polarizer is between the first retarder and the light emitting device such that the ambient light passes through the transparent surface, then the first retarder, and then the first linear polarizer before being received by the light sensor.

3. The electronic device of claim 2 wherein:

the light sensor is adjacent the light emitting device and a photosensitive surface of the light sensor is at substantially the same distance from the transparent surface as a light emitting surface of the light emitting device, such that light emitted by the light emitting device is not directly incident on the photosensitive surface of the light sensor; and

the electronic device further comprises an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit providing an ambient light level value responsive to light incident on the photosensitive surface of the light sensor.

4. The electronic device of claim 2 wherein:

the light emitting device is between the transparent surface and the light sensor;

the light sensor includes a first channel receiving light from both the light emitting device and the ambient light, and providing a first light level value; and

the light sensor includes a second channel with a second linear polarizer oriented to attenuate the ambient light that has been polarized by the first linear polarizer, the second channel receiving light from the light emitting device, and providing a second light level value.

5. The electronic device of claim 4 further comprising an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit providing an ambient light level value responsive to the difference between the first light level value and the second light level value.

6. The electronic device of claim 1 wherein the first retarder is between the first linear polarizer and the light emitting device such that the ambient light passes through the transparent surface, then the first linear polarizer, and then the first retarder before being received by the light sensor.

7. The electronic device of claim 6 wherein:

the light emitting device is between the transparent surface and the light sensor;

the light sensor includes a first channel receiving light from both the light emitting device and ambient light, and providing a first light level value; and

the light sensor includes a second channel with a second retarder and a second linear polarizer oriented to attenuate the ambient light that has been linearly polarized by the second retarder, the second channel receiving light from the light emitting device, and providing a second light level value.

8. The electronic device of claim 7 further comprising an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit providing an ambient light level value responsive to the difference between the first light level value and the second light level value.

9. A method for detecting an ambient light level falling on a transparent surface of an electronic device that includes a light emitting device that emits light through the transparent surface, the method comprising:

placing a first retarder between the transparent surface and the light emitting device;

placing a first linear polarizer between the transparent surface and the light emitting device; and

receiving ambient light that falls on the transparent surface and then passes through the first retarder and the first linear polarizer with a light sensor.

10. The method of claim 9 wherein the first linear polarizer is placed between the first retarder and the light emitting device such that the ambient light passes through the transparent surface, then the first retarder, and then the first linear polarizer before being received by the light sensor.

11. The method of claim 10 further comprising providing an ambient light level value responsive to light incident on the light sensor.

12. The method of claim 10 wherein the light emitting device is between the transparent surface and the light sensor, the method further comprising:

receiving the ambient light with a first channel of the light sensor, the first channel also receiving light emitted by the light emitting device;

receiving the light emitted by the light emitting device with a second channel of the light sensor;

attenuating the ambient light directed to the second channel with a second linear polarizer; and

providing an ambient light level value responsive to the difference between the first channel and the second channel.

13. The method of claim 9 wherein the first retarder is between the first linear polarizer and the light emitting device such that the ambient light passes through the transparent surface, then the first linear polarizer, and then the first retarder before being received by the light sensor, and the light emitting device is between the transparent surface and the light sensor, the method further comprising:

receiving the ambient light with a first channel of the light sensor, the first channel also receiving light emitted by the light emitting device;

receiving the light emitted by the light emitting device with a second channel of the light sensor;

attenuating the ambient light directed to the second channel with a second retarder and a second linear polarizer; and

providing an ambient light level value responsive to the difference between the first channel and the second channel.

14. Means for detecting an ambient light level falling on a transparent surface of an electronic device that includes a means for emitting light through the transparent surface, the means comprising:

first means for circularly polarizing light placed between the transparent surface and the means for emitting light;

first means for linearly polarizing light placed between the transparent surface and the means for emitting light; and

means for receiving ambient light that falls on the transparent surface and then passes through the first means for circularly polarizing light and the first linear polarizer.

15. The means for detecting an ambient light level of claim 14 wherein the first means for linearly polarizing light is placed between the first means for circularly polarizing light and the means for emitting light such that the ambient light passes through the transparent surface, then the first means for circularly polarizing light, and then the first means for linearly polarizing light before being received by the means for receiving ambient light.

16. The means for detecting the ambient light level of claim 15 further comprising means for providing an ambient light level value responsive to light incident on the means for receiving ambient light.

17. The means for detecting the ambient light level of claim 15 wherein the means for emitting light is between the transparent surface and the means for receiving ambient light, and the means for receiving ambient light further comprises:

means for receiving the ambient light and also receiving light emitted by the means for emitting light;

means for receiving only the light emitted by the light emitting device;

means for attenuating the ambient light directed to the means for receiving only the light emitted by the light emitting device; and

means for providing an ambient light level value responsive to the difference between the means for receiving the ambient light and also receiving light emitted by the means for emitting light and the means for receiving only the light emitted by the light emitting device.

18. The means for detecting the ambient light level of claim 14 wherein the first means for circularly polarizing light is between the first means for linearly polarizing light and the means for emitting light such that the ambient light passes through the transparent surface, then the first means for linearly polarizing light, and then the first means for circularly polarizing light before being received by the light sensor, the light emitting device is between the transparent surface and the light sensor, and the means for receiving ambient light further comprises:

receiving the ambient light with a first channel of the light sensor, the first channel also receiving light emitted by the means for emitting light;

receiving the light emitted by the means for emitting light with a second channel of the light sensor;

attenuating the ambient light directed to the second channel with a second retarder and a second linear polarizer; and

providing an ambient light level value responsive to the difference between the first channel and the second channel.

means for receiving the ambient light and also receiving light emitted by the means for emitting light;

means for receiving only the light emitted by the light emitting device;

means for attenuating the ambient light directed to the means for receiving only the light emitted by the light emitting device; and

means for providing an ambient light level value responsive to the difference between the means for receiving the ambient light and also receiving light emitted by the means for emitting light and the means for receiving only the light emitted by the light emitting device.