Ambient light sensors with photodiode leakage current compensation

• US 9,116,043 B2
• Filed: 03/18/2013
• Issued: 08/25/2015
• Est. Priority Date: 03/18/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Zheng, Dong
• Primary Examiner(s): OSORIO, RICARDO
• Application Number:
  US13/845,641
• Publication Number:
  US 20140267202A1
• Time in Patent Office: 890 Days
• Field of Search: 345/207, 345/175, 250/214.AL, 250/214, 348/227.1, 348/336, 348/602
• US Class Current: 1/1
• CPC Class Codes: G01J 1/10 by comparison with reference light or electric value provisionally void
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 5/10 Intensity circuits

Abstract

An electronic device may have a display with a brightness that is adjusted based on data gathered from one or more ambient light sensors (ALSs). In one suitable arrangement, an ALS may include a photodiode, a temperature sensor, a scaler, an analog-to-digital converter (ADC), and a subtractor. The subtractor may have a first input coupled to the photodiode via the ADC, a second input coupled to the temperature sensor via the scaler, and an output on which a leakage-compensated sensor output is provided. In another suitable arrangement, the ALS may include first and second photodiodes, a light blocking layer formed over the second photodiode, a scaler, and a subtractor. The subtractor may have a first input coupled to the first photodiode, a second input coupled to the second photodiode via the scaler, and an output on which a leakage-compensated sensor output is provided.

Claims

1. An electronic device, comprising:

an ambient light sensor that includes a photosensitive element and a temperature sensor, wherein the ambient light sensor is configured to generate a leakage-compensated output signal based only on information gathered from the photosensitive element and the temperature sensor; and

a display having an adjustable brightness level, wherein the brightness of the display is adjusted based only on the leakage-compensated output signal.

2. The electronic device defined in claim 1, wherein the photosensitive element comprises a photodiode.

3. The electronic device defined in claim 1, wherein the ambient light sensor further includes:

a scaler circuit that receives a temperature sensor output signal from the temperature sensor, wherein the scaler circuit produces a corresponding scaled leakage current signal based on the temperature sensor output signal.

4. The electronic device defined in claim 3, wherein the ambient light sensor further includes:

an analog-to-digital converter having an input that is coupled to the photosensitive element and an output on which a corresponding total current signal is provided.

5. The electronic device defined in claim 4, wherein the ambient light sensor further includes:

a subtraction circuit having a first input that receives the total current signal from the analog-to-digital converter, a second input that receives the scaled leakage current signal from the scaler circuit, and an output on which the leakage-compensated output signal is provided.

6. The electronic device defined in claim 5, wherein the ambient light sensor further includes:

a switching circuit coupled between the scaler circuit and second input of the subtraction circuit, wherein the switching circuit is turned off during calibration operation and is turned on during normal operation.

7. The electronic device defined in claim 1, wherein the ambient light sensor further includes:

a scaler circuit that receives a temperature sensor output signal from the temperature sensor and that produces a corresponding scaled leakage current signal based on a look-up table.

8. The electronic device defined in claim 1, wherein the information comprises ambient light level and temperature information.

9. A method of adjusting display brightness for a display in an electronic device that has an ambient light sensor while the electronic device is operated in an environment in which the electronic device is exposed to ambient light, the method comprising:

measuring a total ambient light level for the ambient light with a photosensitive element in the ambient light sensor;

obtaining temperature information on the ambient light sensor with a temperature sensor in the ambient light sensor;

outputting a leakage-compensated ambient light sensor output signal based only on the total ambient light level and the temperature information; and

adjusting display brightness for the display based only on the leakage-compensated ambient light sensor output signal.

10. The method defined in claim 9, further comprising:

obtaining a leakage level associated with the photosensitive element based only on the temperature information, wherein outputting the leakage-compensated ambient light sensor output signal comprises computing a difference between the total ambient light level and the leakage level.

11. The method defined in claim 9, further comprising:

obtaining a leakage level associated with the photosensitive element based on a look-up table.

12. The method defined in claim 9, further comprising:

computing a leakage level associated with the photosensitive element based on a formula derived from measurements obtained during calibration operations.