Distance sensing by IQ domain differentiation of time of flight (TOF) measurements

• US 8,760,631 B2
• Filed: 12/28/2010
• Issued: 06/24/2014
• Est. Priority Date: 01/27/2010
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Ritter, David W., Hiromi, Itaru
• Primary Examiner(s): Alsomiri, Isam
• Assistant Examiner(s): RODRIGUEZ, VICENTE M
• Application Number:
  US12/979,726
• Publication Number:
  US 20110181861A1
• Time in Patent Office: 1,274 Days
• Field of Search: 356/3
• US Class Current: 356/3
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: H01L 31/101 Devices sensitive to infrared, visible or ultraviolet radiation

Abstract

A system and method for identifying a position of a moving object, regardless of static objects present in the optical field of an active infrared (IR) proximity detector, is provided. Moreover, a modulated light emitting diode (LED) signal is captured and processed through I/Q demodulation. Specifically, the reflections received at an IR sensor are demodulated to generate in-phase (I) and quadrature phase (Q) signals and the derivative of I/Q signals is obtained to isolate motion. For example, an I/Q domain differentiator or a high pass filter is employed to calculate the derivative, which actively remove the effects of all forms of static interference. Further, the phase of the derivative I/Q signals is determined and is utilized to reconstruct the distance at which the motion occurred.

Claims

1. A method for use with a system that includes an optical sensor and that is configured to determine at least one of a distance or presence of one or more moving objects relative to the optical sensor, the method comprising:

(a) driving a light emitting element with a drive signal to thereby cause a light signal to be emitted;

(b) producing a sensor signal that is indicative of a portion of the light signal that reflects from one or more objects and is incident on the optical sensor;

(c) performing quadrature demodulation of the sensor signal to produce in-phase (I) and quadrature phase (Q) signals;

(d) determining derivatives of the in-phase (I) and quadrature-phase (Q) signals; and

(e) determining a phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals.

2. The method of claim 1, wherein when there are one or more moving objects and one or more static objects within a sensor field of the optical sensor:

the sensor signal produced at step (b) and the in-phase (I) and quadrature-phase (Q) signals produced at step (c) are indicative of both reflections from the one or more moving objects and reflections from the one or more static objects within the sensor field of the optical sensor; and

the derivatives of the in-phase (I) and quadrature-phase (Q) signals determined at step (d) are indicative of the reflections from the one or more moving objects and are generally not indicative of the reflections from the one or more static objects within the sensor field of the optical sensor.

3. The method of claim 1, further comprising:

(f) using the phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals to determine at least one of a distance or presence of one or more moving objects within a sensor field of the optical sensor.

4. The method of claim 1, further comprising:

(f) using the phase of the derivatives of the in-phase (I) and quadrature-phase (Q) signals to calibrate the system with which the method is being used, thereby enabling the system to determine at least one of a distance or presence of one or more moving objects within a sensor field of the optical sensor based on non-differentiated in-phase (I) and quadrature-phase (Q) signals in a manner that compensates for one or more static objects within the sensor field of the optical sensor.

5. The method of claim 1, wherein:

step (d) is performed using analog circuitry configured to determine derivatives of the in-phase (I) and quadrature-phase (Q) signals.

6. The method of claim 5, wherein:

step (d) includes low pass filtering outputs of the analog circuitry configured to determine derivatives of the in-phase (I) and quadrature-phase (Q) signals to thereby filter out at least some noise introduced by the analog circuitry.

7. The method of claim 1, wherein step (d) includes:

(d.1) converting the in-phase (I) and quadrature-phase (Q) signals produced at step (c) into digital in-phase (I) and quadrature-phase (Q) signals, respectively;

(d.2) determining the derivative of the digital in-phase (I) signal by subtracting a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal; and

(d.3) determining the derivative of the digital quadrature-phase (Q) signal by subtracting a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal.

8. The method of claim 7, wherein the subtracting at steps (d.2) and (d.3) are performed in accordance with a fixed sampling rate.

9. The method of claim 7, wherein the subtracting at steps (d.2) and (d.3) are performed in accordance with a variable sampling rate that ensures that results of the subtracting are at least as large as a threshold value.

10. The method of claim 1, wherein the light signal, produced in response to the driving at step (a), has a frequency within a range of 1 MHz-50 MHz.

11. A system, comprising:

a driver configured to produce a drive signal that drives a light emitting element to thereby cause a light signal to be emitted;

an optical sensor configured to produce a sensor signal that is indicative of a portion of the light signal that reflects from one or more objects and is incident on the optical sensor;

a demodulator configured to perform quadrature demodulation of the sensor signal to produce in-phase (I) and quadrature phase (Q) signals;

a differentiator configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals; and

a phase detector configured to determine a phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals.

12. The system of claim 11, wherein when there are one or more moving objects and one or more static objects within a sensor field of the optical sensor:

the sensor signal produced by the optical sensor and the in-phase (I) and quadrature-phase (Q) signals produced by the demodulator are indicative of both reflections from the one or more moving objects and reflections from the one or more static objects within the sensor field of the optical sensor; and

the derivatives of the in-phase (I) and quadrature-phase (Q) signals determined by the differentiator are indicative of reflections from one or more moving objects and are generally not indicative of reflections from one or more static objects within the sensor field of the optical sensor.

13. The system of claim 11, further comprising:

circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to determine at least one of a distance or presence of one or more moving objects within a sensor field of the optical sensor.

14. The system of claim 11, further comprising:

circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to calibrate further circuitry configured to determine at least one of a distance or presence of one or more moving objects based on non-differentiated in-phase (I) and quadrature phase (Q) signals;

wherein the calibration compensates for one or more static objects within a sensor field of the optical sensor.

15. The system of claim 11, wherein the differentiator comprises analog circuitry configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals.

16. The system of claim 15, wherein the differentiator further comprises a low pass filter configured to low pass filter outputs of the analog circuitry configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals to thereby filter out at least some noise introduced by the analog circuitry.

17. The system of claim 11, wherein the differentiator includes:

an analog-to-digital converter (ADC) configured to convert the in-phase (I) signal produced by the demodulator into a digital in-phase (I) signal;

an analog-to-digital converter (ADC) configured to convert the quadrature-phase (Q) signal produced by the demodulator into a digital quadrature-phase (Q) signal;

circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal; and

circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal.

18. The system of claim 17, wherein the circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal, and the circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal, each perform said corresponding subtraction in accordance with a fixed sampling rate.

19. The system of claim 17, wherein the circuitry configured to subtract a delayed value of the digital in-phase (I) signal from a current value of the digital in-phase (I) signal, and the circuitry configured to subtract a delayed value of the digital quadrature-phase (Q) signal from a current value of the digital quadrature-phase (Q) signal, each perform said corresponding subtraction in accordance with a variable sampling rate that ensures that results of the subtracting are at least as large as a threshold value.

20. The system of claim 11, wherein the light signal, produced in response to the drive signal, has a frequency within a range of 1 MHz-50 MHz.

21. A subsystem for use with a system that includes

a driver configured to produce a drive signal that drives a light emitting element to thereby cause a light signal to be emitted;

and

an optical sensor configured to produce a sensor signal that is indicative of a portion of the light signal that reflects from one or more objects and is incident on the optical sensor;

wherein the subsystem comprises;

a demodulator configured to perform quadrature demodulation of the sensor signal to produce in-phase (I) and quadrature phase (Q) signals;

a differentiator configured to determine derivatives of the in-phase (I) and quadrature phase (Q) signals; and

a phase detector configured to determine a phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals;

wherein when there are one or more moving objects and one or more static objects within a sensor field of the optical sensor,

the in-phase (I) and quadrature-phase (Q) signals produced by the demodulator are indicative of both reflections from the one or more moving object and reflections from the one or more static objects within the sensor field of the optical sensor, and

the derivatives of the in-phase (I) and quadrature-phase (Q) signals determined by the differentiator are indicative of reflections from one or more moving objects and are generally not indicative of reflections from one or more static objects within the sensor field of the optical sensor.

22. The subsystem of claim 21, further comprising:

circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to determine at least one of a distance or presence of one or more moving objects within the sensor field of the optical sensor.

23. The subsystem of claim 21, further comprising:

circuitry configured to use the phase of the derivatives of the in-phase (I) and quadrature phase (Q) signals to calibrate further circuitry configured to determine at least one of a distance or presence of one or more moving objects within the sensor field of the optical sensor based on non-differentiated in-phase (I) and quadrature phase (Q) signals;

wherein the calibration compensates for one or more static objects within the sensor field of the optical sensor.