PROXIMITY SENSORS WITH IMPROVED AMBIENT LIGHT REJECTION

• US 20110006188A1
• Filed: 03/02/2010
• Published: 01/13/2011
• Est. Priority Date: 07/07/2009
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Lin, Xijian
• Granted Patent: US 8,222,591 B2
• Time in Patent Office: Days
• US Class Current: 250/201.1
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/4876 by removing unwanted signals G01S7/495 takes precedence
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: H03K 17/941 using an optical detector H03K17/968 takes precedence
• CPC Class Codes: H03K 2217/94108 making use of reflection

Abstract

In accordance with an embodiment, a proximity sensor includes a driver, a photodiode (PD), an analog-to-digital converter (ADC) with analog-to-digital-to-analog (ADA) feedback, and a controller. The driver is adapted to selectively drive a light source. The photodiode (PD) is adapted to produce a photodiode current signal (Idiode) indicative of an intensity of light detected by the PD, where the light detected by the PD can include ambient light and/or light transmitted by the light source that was reflected off an object proximate the PD. The controller is adapted to control the driver and the ADC with ADA feedback. A digital output of the ADC with ADA feedback is indicative of a proximity of an object to the PD with at least a majority of the ambient light detected by the PD rejected.

Claims

1. A proximity sensor, comprising:

a driver adapted to selectively drive a light source;

a photodiode (PD) adapted to produce a photodiode current signal (Idiode) indicative of an intensity of light detected by the PD, where the light detected by the PD can include ambient light and/or light transmitted by the light source that was reflected off an object proximate the PD;

an analog-to-digital converter (ADC) with analog-to-digital-to-analog (ADA) feedback; and

a controller adapted to control the driver and the ADC with ADA feedback;

wherein a digital output of the ADC with ADA feedback is indicative of a proximity of an object to the PD with at least a majority of the ambient light detected by the PD rejected.

2. The proximity sensor of claim 1, wherein the ADC with the ADA feedback comprises:

an M-bit ADC adapted to

receive a first analog signal indicative of an intensity of light detected by the PD 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 light detected by the PD 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 light detected by the PD 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 the light detected by the PD 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 PD 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 output of 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.

3. The proximity sensor of claim 2, 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.

4. The proximity sensor of claim 3, wherein 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 PD with at least a majority of ambient light detected by the PD rejected.

5. The proximity sensor of claim 2, wherein:

M<

N.

6. The proximity sensor of claim 2, wherein:

M≧

N.

22. The proximity sensor of claim 1, wherein at least some components are shared by both the N-bit ADC and the M-bit ADC.

7. A proximity sensor, comprising:

a driver adapted to selectively drive a light source;

a photodiode (PD);

an M-bit ADC adapted to

receive a first analog signal indicative of an intensity of light detected by the PD 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 light detected by the PD 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 light detected by the PD 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 the light detected by the PD 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 PD 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 indicative of a proximity of an object to the PD with at least a majority of ambient light detected by the PD rejected; and

a controller that controls M-bit ADC, the M-bit DAC and the N-bit ADC;

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.

8. The proximity sensor of claim 7, wherein the controller also controls the driver.

9. The proximity sensor of claim 7, 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.

10. The proximity sensor of claim 9, wherein 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 PD with at least a majority of ambient light detected by the PD rejected.

11. The proximity sensor of claim 7, wherein:

M<

N.

12. The proximity sensor of claim 7, wherein:

M≧

N.

13. A method for use with a light source and a photodiode (PD), comprising:

(a) selectively driving the light source;

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

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

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

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

(f) converting the third analog signal to N-bits of data indicative of a proximity of an object to the PD with at least a majority of ambient light detected by the PD rejected;

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.

14. The method of claim 13, further comprising:

(e) enabling, disabling or adjusting operation of a subsystem based on the N-bits of data produced at step (f).

15. The method of claim 13, wherein:

M<

N.

16. The method of claim 13, wherein:

M≧

N.

17. A system, comprising:

a driver adapted to selectively drive a light source;

a photodiode (PD) adapted to produce a photodiode current signal indicative of an intensity of light detected by the PD, where the light detected by the PD can include ambient light and/or light transmitted by the light source that was reflected off an object proximate the PD;

an analog-to-digital converter (ADC) with analog-to-digital-to-analog (ADA) feedback, wherein a digital output of the ADC with ADA feedback is indicative of a proximity of an object to the PD with at least a majority of the ambient light detected by the PD rejected;

a controller adapted to control the driver and the ADC with ADA feedback;

a subsystem capable of being enabled and disabled; and

a comparator or processor that receives digital output of the ADC with ADA feedback and enables or disables the subsystem based on the digital output of the ADC with ADA feedback.

18. The system of claim 17, wherein the subsystem is selected from the group consisting of:

a touch-screen,

a display,

a backlight,

a virtual scroll wheel,

a virtual keypad, and

a navigation pad.

19. The system of claim 17, wherein the ADC with ADA feedback comprises:

an M-bit ADC adapted to

receive a first analog signal indicative of an intensity of light detected by the PD 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 light detected by the PD 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 light detected by the PD 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 the light detected by the PD 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 PD 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 output of 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.

20. The system of claim 19, 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.

21. The system of claim 20, wherein 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 PD with at least a majority of ambient light detected by the PD rejected.