Ambient light sensor with internal light cancellation

• US 9,612,152 B2
• Filed: 11/07/2013
• Issued: 04/04/2017
• Est. Priority Date: 11/07/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: deJong, Erik G., Guillou, Jean-Pierre S., Aflatooni, Koorosh
• Primary Examiner(s): LEE, JOHN R
• Application Number:
  US14/074,547
• Publication Number:
  US 20150122978A1
• Time in Patent Office: 1,244 Days
• 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 sensor;

a light emitting device between the transparent surface and the light sensor, the light emitting device to emit light through the transparent surface;

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

a first linear polarizer between the first retarder and the light emitting device;

wherein the light sensor is for receiving ambient light that passes through the transparent surface, then the first retarder, and then the first linear polarizer, the light sensor including

a first channel for receiving both light from the light emitting device and ambient light, and to provide a first light level value, and

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

2. The electronic device of claim 1 further comprising an ambient light detection circuit coupled to the light sensor, the ambient light detection circuit configured to provide an ambient light level value responsive to a difference between the first light level value and the second light level value.

3. A method for detecting an ambient light level falling on a transparent surface of an electronic device with a light sensor, the electronic device including a light emitting device between the light sensor and the transparent surface, the light emitting device to emit 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 first retarder and the light emitting device;

receiving ambient light that falls on the transparent surface and then passes through the transparent surface, then the first retarder, and then the first linear polarizer with a first channel of the light sensor, the first channel also receiving the 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 ambient light directed to the second channel with a second linear polarizer; and

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

4. An electronic device comprising:

a transparent surface;

means for sensing light

means for emitting light through the transparent surface, the means for emitting light placed between the means for sensing light and the transparent surface;

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 and also receiving light emitted by the means for emitting light, the ambient light falling on the transparent surface and then passing through the first transparent surface, the means for circularly polarizing light, and the means for linearly polarizing light;

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

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

5. An electronic device comprising:

a transparent surface;

a light sensor;

a light emitting device between the transparent surface and the light sensor, the light emitting device to emit light through the transparent surface;

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

a first retarder between the first linear polarizer and the light emitting device;

wherein the light sensor is positioned to receive ambient light that passes through the transparent surface, then the first linear polarizer, and then the first retarder, the light sensor including

a first channel positioned to receive light from both the light emitting device and ambient light, and configured to provide a first light level value, and

a second channel with a second retarder and a second linear polarizer oriented to attenuate ambient light that has been linearly polarized by the second retarder, the second channel positioned to receive light from the light emitting device, and configured to provide a second light level value.

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

7. A method for detecting an ambient light level falling on a transparent surface of an electronic device with a light sensor, the electronic device including a light emitting device between the light sensor and the transparent surface, the light emitting device emitting light through the transparent surface, the method comprising:

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

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

receiving ambient light that falls on the transparent surface and then passes through the transparent surface, then the first linear polarizer, and then the first retarder 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 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 a difference between the first channel and the second channel.