Ambient Light Sensors with Photodiode Leakage Current Compensation

• US 20140267202A1
• Filed: 03/18/2013
• Published: 09/18/2014
• Est. Priority Date: 03/18/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Zheng, Dong
• Granted Patent: US 9,116,043 B2
• Time in Patent Office: Days
• US Class Current: 345/207
• 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 on information gathered from the photosensitive element and the temperature sensor.

2. The electronic device defined in claim 1, further comprising:

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

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

4. 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.

5. The electronic device defined in claim 4, 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.

6. The electronic device defined in claim 5, 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.

7. The electronic device defined in claim 6, 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.

8. An electronic device, comprising:

an ambient light sensor that includes a first photosensitive element and second photosensitive element that is smaller than the first photosensitive element, wherein the ambient light sensor is configured to generate an ambient light sensor output signal based on information gathered from the first and second photosensitive elements.

9. The electronic device defined in claim 8, further comprising:

a display having an adjustable brightness level, wherein the brightness level of the display is adjusted based on the ambient light sensor output signal generated by the ambient light sensor.

10. The electronic device defined in claim 8, wherein the first and second photosensitive elements comprise photodiodes.

11. The electronic device defined in claim 8, wherein the ambient light sensor further includes:

a light blocking layer formed over the second photosensitive element so that the second photosensitive element is prevented from receiving ambient light.

12. The electronic device defined in claim 8, wherein the ambient light sensor further includes:

a subtraction circuit having a first input, a second input, and an output;

a first data converter coupled between the first photosensitive element and the first input of the subtraction circuit;

a second data converter coupled between the second photosensitive element and the second input of the subtraction circuit; and

a scaler circuit interposed between the second data converter and the second input of the subtraction circuit, wherein the subtraction circuit is configured to receive at its first input a total current signal from the first data converter, to receive at its second input a scaled leakage current signal from the scaler circuit, and to generate at its output the ambient light sensor output signal.

13. The electronic device defined in claim 8, wherein the ambient light sensor further includes:

a subtraction circuit having a first input, a second input, and an output;

a data converter having an input that is switchably coupled to a selected one of the first and second photosensitive elements and an output; and

first and second data storage elements, wherein the first input of the subtraction circuit is switchably coupled to the data converter via the first data storage element, wherein the second input of the subtraction circuit is switchably coupled to the data converter via the second data storage element and a scaler circuit, and wherein the subtraction circuit is configured to receive at its first input a total current signal from the first data storage element, to receive at its second input a scaled leakage current signal from the scaler circuit, and to generate at its output the ambient light sensor output signal.

14. The electronic device defined in claim 8, wherein the ambient light sensor further includes:

an analog current subtraction circuit having a first input that is coupled to the first photosensitive element, a second input that is coupled to the second photosensitive element, and an output;

an analog current mirror circuit interposed between the second photosensitive element and the second input of the analog current subtraction circuit; and

a data converter coupled to the output of the analog current subtraction circuit.

15. 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 a leakage level associated with the photosensitive element; and

outputting a leakage-compensated ambient light sensor output signal based on the total ambient light level and the leakage level.

16. The method defined in claim 15, wherein outputting the leakage-compensated ambient light sensor output signal based on the total ambient light level and the leakage level comprises computing a difference between the total ambient light level and the leakage level.

17. The method defined in claim 15, further comprising:

obtaining temperature information on the ambient light sensor with a temperature sensor in the ambient light sensor, wherein obtaining the leakage level comprises obtaining the leakage level based on the obtained temperature information.

18. The method defined in claim 15, further comprising:

measuring a leakage current with an additional photosensitive element in the ambient light sensor, wherein the additional photosensitive element is smaller than the photosensitive element, and wherein obtaining the leakage level comprises obtaining the leakage level based on the leakage current measured by the additional photosensitive element.

19. The method defined in claim 18, further comprising:

with a scaling circuit in the ambient light sensor, scaling the leakage current measured from the additional photosensitive element by a predetermined scaling factor.

20. The method defined in claim 15, further comprising:

with data converter circuitry and time-multiplexing circuitry in the ambient light sensor, computing the total ambient light level during a first time period and computing the leakage level during a second time period that is different than the first time period.