System and Circuit Including Multiple Photo Detectors

• US 20110248151A1
• Filed: 11/17/2010
• Published: 10/13/2011
• Est. Priority Date: 04/13/2010
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Svajda, Miroslav, Holcombe, Wayne T.
• Granted Patent: US 8,569,679 B2
• Time in Patent Office: Days
• US Class Current: 250/221
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G01S 3/7803 Means for monitoring or calibrating
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4913 Circuits for detection, sampling, integration or read-out
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/4972 Alignment of sensor
• CPC Class Codes: G01V 8/20 using multiple transmitters or receivers

Abstract

A system includes a plurality of photo detectors, which generate signals proportional to incident light. The system further includes an optical barrier adjacent to a surface and includes a control circuit. The optical barrier partially obstructs reflected light from reaching the plurality of photo detectors to produce a spatially dependent reflectance pattern that is dependent on a position of an object relative to a substrate. The control circuit determines a position of the object during a reflectance measurement cycle using each of the plurality of photo detectors by calibrating to ambient light conditions, measuring ambient plus reflected light, determining the reflected light and detecting the position of the object based on a ratio of the reflected light received by at least two of the plurality of photo detectors.

Claims

1. A system comprising:

a plurality of photo detectors, each of the plurality of photo detectors configured to generate signals proportional to incident light;

an optical barrier configured to partially obstruct reflected light from reaching the plurality of photo detectors to produce a spatially dependent reflectance pattern that is dependent on a position of an object relative to a substrate; and

a control circuit configured to determine a position of the object during a reflectance measurement cycle using each of the plurality of photo detectors, the control circuit to;

calibrate each of the plurality of photo detectors to ambient light conditions;

measure ambient plus reflected light using each of the plurality of photo detectors;

correct the ambient plus reflected light based on the ambient light conditions to determine the reflected light received by each of the plurality of photo detectors; and

detect the position of the object based on a ratio of the reflected light received by at least two of the plurality of photo detectors.

2. The system of claim 1, wherein the control circuit is further configured to iteratively repeat the reflectance measurement cycle and to detect motion of the object in response to a change in the ratio over time.

3. The system of claim 2, wherein the control circuit iteratively measures the ambient light and the ambient plus reflected light at each of the plurality of photo detectors to determine the reflected light during each repetition of the reflectance measurement cycle.

4. The system of claim 1, wherein, to calibrate and measure using each of the plurality of photo detectors, the control circuit is configured to:

select a photo detector of the plurality of photo detectors;

measure the ambient light using the photo detector;

activate a light source;

measure the ambient plus reflected light using the photo detector; and

turn off the light source; and

select a next photo detector for repeatedly measuring the ambient light and the ambient plus reflected light.

5. The system of claim 1, wherein the control circuit differentiates light variations due to motion of the object versus bulk ambient changes.

6. The system of claim 1, wherein the optical barrier comprises multiple barrier elements arranged in a pattern to produce the spatially dependent reflectance pattern.

7. The system of claim 6, wherein the pattern comprises:

a first portion extending in a first direction; and

a second portion extending in a second direction that is substantially perpendicular to the first direction.

8. A circuit comprising:

a plurality of photo detectors, the plurality of photo detectors configured to generate electrical signals based on received light including at least one of ambient light and light variations caused by an object moving proximate to a substrate;

an optical barrier adapted to produce a non-uniform reflectance pattern over the plurality of photo detectors from the light variations caused by the object; and

a control circuit coupled to the plurality of photo detectors to receive the electrical signals, determine the light variations from the electrical signals, and determine a change in position of the object based on variation ratios of the light variations received by pairs of photo detectors of the plurality of photo detectors in response to determining the light variations.

9. The circuit of claim 8, wherein the control circuit is configured to:

select one of the plurality of photo detectors;

deactivate a light source;

receive a first electrical signal from the one of the plurality of photo detectors, the first electrical signal corresponding to the ambient light;

activate the light source;

receive a second electrical signal from the one of the plurality of photo detectors, the second electrical signal corresponding to ambient light plus light variations; and

determine the light variations at the one of the plurality of photo detectors based on a difference between the first electrical signal and the second electrical signal.

10. The circuit of claim 9, wherein the control circuit is further configured to:

iteratively select from the plurality of photo detectors;

iteratively deactivate and activate the light source; and

iteratively receive the first electrical signal, receive the second electrical signal, and determine the light variations at each of the plurality of photo detectors.

11. The circuit of claim 8, wherein each of the plurality of photo detectors receives the light such that the light variations received by the photo detector are spatially dependent on the position of the object relative to the substrate.

12. The circuit of claim 8, wherein the control circuit is configured to detect motion of the object when an absolute value of a change in one or more of the variation ratios exceeds a threshold.

13. The circuit of claim 8, wherein the control circuit differentiates light variations due to motion of the object versus bulk ambient changes.

14. The circuit of claim 8, wherein the optical barrier extends in a direction that is substantially perpendicular to a surface of the substrate.

15. The circuit of claim 8, wherein the optical barrier is formed on a surface of the substrate.

16. The circuit of claim 8, wherein the optical barrier is formed on a transparent package deposited over the substrate.

17. The circuit of claim 8, wherein the optical barrier comprises opaque ink that is printed in a pattern above a surface of the substrate.

18. The circuit of claim 8, wherein the plurality of barrier elements are arranged to form at least one of an intersecting line pattern, a parallel line pattern, a ring pattern, a rectangular pattern, and an arc pattern.

19. A system comprising:

a substrate including an active surface;

a light-emitting diode configured to emit light above the active surface;

a plurality of photo detectors disposed in the substrate adjacent to the active surface,

an optical barrier adjacent to the active surface and configured to produce a spatially dependent reflectance pattern over the plurality of photo detectors based on reflectance of light by an object; and

a control circuit configured to control activation of the light-emitting diode and to sequentially sample incident light with the light-emitting diode deactivated and a reflectance with the light-emitting diode activated using each photo detector of the plurality of photo detectors, the control circuit to determine position of an object relative to the substrate based on ratios of reflectances between adjacent photo detectors of the plurality of photo detectors.

20. The system of claim 19, wherein the control circuit is configured to detect motion of the object in response to a change in one of the ratios of reflectances over time.

21. The system of claim 19, wherein the plurality of photo detectors detect reflected light in a respective plurality of optical detection regions defined in part by the optical barrier.

22. The system of claim 19, wherein the plurality of barrier elements defines a pattern including at least one of a concentric ring pattern, a concentric arc pattern, and a rectangular pattern.