DISTANCE SENSING BY IQ DOMAIN DIFFERENTIATION OF TIME OF FLIGHT (TOF) MEASUREMENTS

• US 20110181861A1
• Filed: 12/28/2010
• Published: 07/28/2011
• 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: Hiromi, Itaru, Ritter, David W.
• Granted Patent: US 8,760,631 B2
• Time in Patent Office: Days
• 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. An apparatus for a reflection based long range proximity detector, comprising:

a first circuit that detects reflected light;

a second circuit that generates an electrical signal indicative of the reflected light;

a third circuit that performs quadrature amplitude demodulation to extract in-phase (I) and quadrature-phase (Q) components from the electrical signal;

a fourth circuit that removes a backscatter effect from the I and Q components; and

a fifth circuit that identifies a distance at which a motion occurred based in part on a phase of the derivative of the I and Q components.

2. The apparatus of claim 1, further comprising, a sixth circuit that determines the phase of the derivative of the I and Q components.

3. The apparatus of claim 2, wherein the sixth circuit determines the phase of the I and Q components.

4. The apparatus of claim 1, wherein the first and second circuits are included in an Infrared (IR) detector that at least one of amplifies or filters the electrical signal.

5. The apparatus of claim 1, wherein the fourth circuit includes at least one low pass filter (LPF) to control noise.

6. The apparatus of claim 1, wherein the fourth circuit includes a subtractor circuit which generates a difference between a current value of a signal and a delayed value of the signal.

7. The apparatus of claim 6, wherein the subtractor circuit includes a unit delay generator.

8. The apparatus of claim 6, wherein the fourth circuit generates a discrete derivative of the I and Q components by employing a fixed sampling rate.

9. The apparatus of claim 6, wherein the fourth circuit generates a discrete derivative of the I and Q components by employing a variable sampling rate.

10. The apparatus of claim 9, wherein the fourth circuit generates a clock signal that triggers sampling, based on a comparison of a magnitude of the derivative of the I and Q components and a threshold.

11. The apparatus of claim 1, wherein the apparatus is situated on an integrated circuit chip.

12. The apparatus of claim 1, wherein the apparatus is situated on a plurality of integrated circuit chips.

13. A method that discerns distance at which a motion occurred, comprising:

emitting a frequency modulated light signal;

causing the light signal to reflect from a moving object;

capturing orthogonal components of a portion of the reflected light;

generating an electrical signal indicative of the orthogonal components;

demodulating the electrical signal;

computing a derivative of the electrical signal; and

identifying a distance of the moving object based in part on a phase of the derivative.

14. The method of claim 13, further comprising, calculating a phase of the derivative.

15. The method of claim 13, further comprising, filtering the derivative by employing at least one low pass filter (LPF).

16. The method of claim 13, wherein the computing includes determining a discrete derivative by employing a fixed sampling rate.

17. The method of claim 13, wherein the computing includes determining a discrete derivative by employing a variable sampling rate.

18. The method of claim 13, further comprising, employing the derivative to calibrate an optical motion detector.

19. A system, comprising:

a light emitting diode (LED) that emits a frequency modulated signal, wherein at least a portion of the frequency modulated signal reflects back from a moving object;

a sensor that generates an electric signal based on the reflected portion of the frequency modulated signal;

an I/Q demodulation circuit generates an in-phase (I) and a quadrature-phase (Q) signal by demodulating the electrical signal;

an I/Q differentiation circuit that generates an output signal indicative of a derivative of the I and Q signals; and

a phase determination circuit that determines a phase of the output signal, wherein the phase is indicative of the distance of the moving object from the sensor.

20. The system of claim 19, further comprising, a circuit to identify a distance at which motion occurred based on the phase of the output signal.