OPTICAL PROXIMITY SENSORS WITH OFFSET COMPENSATION

• US 20130120761A1
• Filed: 01/27/2012
• Published: 05/16/2013
• Est. Priority Date: 11/11/2011
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Dyer, Kenneth C., Lin, Xijian
• Granted Patent: US 8,848,202 B2
• Time in Patent Office: Days
• US Class Current: 356/614
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4912 Receivers

Abstract

An optical proximity sensor includes a driver, light detector and offset signal generator. The driver selectively drives a light source. The light detector produces an analog detection signal indicative of an intensity of light detected by the light detector. The detected light can include light transmitted by the light source that reflected off an object within the sense region of the optical sensor, interference light and ambient light. The interference light includes light transmitted by the light source, and detected by the light detector, that was not reflected off an object within the sense region of the optical sensor. The offset signal generator selectively produces an analog offset signal that is combined with the analog detection signal produced by the photodetector to produce an analog compensated detection signal. The analog offset signal compensates for at least a portion of the interference light included in the light detected by the photodetector.

Claims

1. An optical proximity sensor that can be used to detect the presence, proximity and/or motion of an object within the sense region of the optical proximity sensor, comprising:

a driver adapted to selectively drive a light source to transmit light;

a light detector adapted to produce an analog detection signal indicative of an intensity of light detected by the light detector, wherein the light detected by the light detector can include

light transmitted by the light source that was reflected off an object within the sense region of the optical sensor,

interference light, which comprises light transmitted by the light source, and detected by the light detector, that was not reflected off an object within the sense region of the optical sensor, and

ambient light; and

an offset signal generator adapted to selectively produce an analog offset signal that is combined with the analog detection signal produced by the photodetector to produce an analog compensated detection signal;

wherein the analog offset signal compensates for at least a portion of the interference light included in the light detected by the light detector.

2. The optical proximity sensor of claim 1,

further comprising an analog-to-digital converter (ADC) adapted to convert the analog compensated detection signal to a digital compensated detection signal;

and

wherein the analog offset signal is combined with the analog detection signal to produce the analog compensated detection signal, prior to conversion by the ADC of the analog compensated detection signal to the digital compensated detection signal, which thereby increases the dynamic range of the ADC.

3. The optical proximity sensor of claim 2, further comprising:

a timing controller configured to produce a transmit signal that is used to synchronize the offset signal generator'"'"'s selective producing of the analog offset signal with the driver'"'"'s selective driving of the light source, so that the analog offset signal is produced at the same time that the light source transmits light.

4. The optical proximity sensor of claim 2, wherein:

the digital compensated detection signal output by the ADC is indicative of a proximity of an object to the light detector with at least a majority of the ambient light detected by the light detector rejected, and with at least a majority of the interference light compensated for.

5. The optical proximity sensor of claim 4, wherein:

the offset signal generator includes a digital-to-analog converter (DAC) that outputs the analog offset signal; and

the DAC of the offset signal generator receives a digital signal indicative of a magnitude of the interference light.

6. The optical proximity sensor of claim 2, wherein:

the offset signal generator includes a digital-to-analog converter (DAC) that outputs the analog offset signal;

the DAC of the offset signal generator receives a digital signal indicative of a magnitude of the interference light and a magnitude of the ambient light; and

the analog offset signal, output by the DAC of the offset signal generator, also rejects at least a portion of the ambient light included in the light detected by the light detector.

7. The optical proximity sensor of claim 4, wherein:

the ADC is an ADC with analog-to-digital-to-analog (ADA) feedback.

8. The proximity sensor of claim 7, wherein the ADC with the ADA feedback comprises:

an M-bit ADC adapted to

receive a first analog signal indicative of an intensity of ambient light detected by the light detector during a first period of time when the light source is not driven to transmit light, and

convert the first analog signal to M-bits of data indicative of the intensity of ambient light detected by the light detector during the first period of time when the light source is not driven to transmit light;

an M-bit digital-to-analog converter (DAC) adapted to

receive the M-bits of data, produced by the M-bit ADC, which are indicative of the intensity of ambient light detected by the light detector during the first period of time when the light source is not driven to transmit light, and

convert the M-bits of data to a second analog signal indicative of the intensity of ambient light detected by the light detector during the first period of time when the light source is not driven to transmit light; and

an N-bit ADC adapted to

receive a third analog signal indicative of an intensity of light detected by the light detector during a further period of time with the second analog signal produced by the M-bit DAC subtracted therefrom, and

convert the third analog signal to N-bits of data, which is the digital offset compensated detection signal output by the ADC with ADA feedback;

wherein during a portion of the further period of time the light source is driven to transmit light, and during another portion of the further period of time the light source is not driven to transmit light.

9. The proximity sensor of claim 8, wherein:

the portion of the further period of time during which the light source is driven to transmit light is shorter than the another portion of the further period of time during which the light source is not driven to transmit light; and

the N-bit ADC includes an up-down counter that counts up during part of the further period of time at least a portion of which the light source is driven to transmit light, and counts down during a remainder of the further period of time, to thereby produce a count value, wherein the count value at the end of the further period of time is the N-bits of data indicative of a proximity of an object to the light detector with at least a majority of ambient light detected by the light detector rejected, and with at least a majority of the interference light compensated for.

10. The optical proximity sensor of claim 1, wherein there is no opaque barrier, between the light source and the light detector, configured to optically isolate the light source from the light detector.

11. A method for use with an optical proximity sensor, including a light source and a light detector, which can be used to detect the presence, proximity and/or motion of an object within the sense region of the optical sensor, the method comprising:

(a) selectively driving the light source to thereby cause the light source to selectively transmit light;

(b) producing an analog detection signal indicative of an intensity of light detected by the light detector, wherein the light detected by the light detector can include

light transmitted by the light source that was reflected off an object within the sense region of the optical sensor,

interference light, which comprises light transmitted by the light source, and detected by the light detector, that was not reflected off an object within the sense region of the optical sensor, and

ambient light;

(c) producing an analog offset signal; and

(d) combining the analog offset signal with the analog detection signal to produce an analog compensated detection signal; and

wherein the analog offset signal compensates for at least a portion of the interference light included in the light detected by the light detector.

12. The method of claim 11, wherein step (c) comprises:

(c.1) storing a digital value; and

(c.2) converting the digital value to the analog offset signal.

13. The method of claim 11, wherein step (c) comprises:

(c.1) storing a first digital value for use in compensating for the interference light;

(c.2) storing a second digital value for use in rejecting the ambient light; and

(c.3) converting the first and second digital values to the analog offset signal;

wherein the analog offset signal also rejects at least a portion of the interference light included in the light detected by the light detector.

14. The method of claim 11, further comprising:

(e) converting the analog compensated detection signal to a digital compensated detection using an analog-to-digital converter (ADC);

wherein the analog offset signal is combined with the analog detection signal to produce the analog compensated detection signal prior to step (e), which thereby increases the dynamic range of the ADC used to perform step (e).

15. The method of claim 14, wherein step (e) comprises:

(e.1) producing a first analog signal indicative of an intensity of light detected by the light detector during a first period of time when the light source is not driven to transmit light;

(e.2) converting the first analog signal to M-bits of data indicative of the intensity of light detected by the light detector during the first period of time when the light source is not driven to transmit light;

(e.3) converting the M-bits of data to a second analog signal indicative of the intensity of the light detected by the light detector during the first period of time when the light source is not driven to transmit light;

(e.4) producing a third analog signal indicative of an intensity of light detected by the light detector during a further period of time with the second analog signal produced by the M-bit DAC subtracted therefrom; and

(e.5) converting the third analog signal to N-bits of data, which is the digital offset compensated detection signal;

wherein during a portion of the further period of time the light source is driven to transmit light, and during another portion of the further period of time the light source is not driven to transmit light.

16. The method of claim 15, wherein step (c) comprises:

(c.1) subtracting an offset target value from values of the digital compensated detection signal to produce a target offset digital compensated detection signal;

(c.2) digitally filtering the target offset digital compensated detection signal to thereby produce a filtered target offset digital compensated detection signal; and

(c.3) converting the target offset digital compensated detection signal to the analog offset signal using a digital-to-analog converter (DAC).

17. A system comprising,

an optical proximity sensor to detect the presence, proximity and/or motion of an object within the sense region of the optical proximity sensor;

a subsystem capable of being enabled and disabled; and

a comparator or processor that receives a digital output of the optical proximity sensor and enables and disables the subsystem based on the digital output of the optical proximity sensor;

wherein the optical proximity sensor includes

a driver adapted to selectively drive a light source to transmit light;

a light detector adapted to produce an analog detection signal indicative of an intensity of light detected by the light detector, wherein the light detected by the light detector can include

light transmitted by the light source that was reflected off an object within the sense region of the optical sensor,

interference light, which comprises light transmitted by the light source, and detected by the light detector, that was not reflected off an object within the sense region of the optical sensor, and

ambient light;

an offset signal generator adapted to selectively produce an analog offset signal that is combined with the analog detection signal produced by the photodetector to produce an analog compensated detection signal;

an analog-to-digital converter (ADC) adapted to convert the analog compensated detection signal to a digital compensated detection signal; and

wherein the analog offset signal compensates for at least a portion of the interference light included in the light detected by the light detector;

wherein the analog offset signal is combined with the analog detection signal to produce the analog compensated detection signal, prior to conversion by the ADC of the analog compensated detection signal to the digital compensated detection signal, which thereby increases the dynamic range of the ADC; and

wherein the digital compensated detection signal comprises the digital output of the optical proximity sensor.

18. The system of claim 17, wherein the optical proximity sensor also includes:

a timing controller configured to produce a transmit signal that is used to synchronize the offset signal generator'"'"'s selective producing of the analog offset signal with the driver'"'"'s selective driving of the light source, so that the analog offset signal is produced at the same time that the light source transmits light.

19. The system of claim 17, wherein:

the ADC of the optical proximity sensor is an ADC with analog-to-digital-to-analog (ADA) feedback; and

a digital output of the ADC with ADA feedback is indicative of a proximity of an object to the light detector with at least a majority of the ambient light detected by the light detector rejected, and with at least a majority of the interference light compensated for.

20. The system of claim 17, wherein there is no opaque barrier, between the light source and the light detector, configured to optically isolate the light source from the light detector.