Multi-Level Digital Modulation for Time of Flight Method and System

• US 20110299059A1
• Filed: 04/07/2011
• Published: 12/08/2011
• Est. Priority Date: 04/07/2010
• Status: Active Grant

• Current Assignee: Ams Sensors Singapore Pte. Ltd. (Ams-Osram AG)
• Original Assignee: MESA IMAGING AG (Ams-Osram AG)
• Inventors: Buettgen, Bernhard, Oggier, Thierry
• Granted Patent: US 9,341,715 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4911 Transmitters

Abstract

The modulation scheme disclosed in this invention report allows for utilizing multiple 3D time-of-flight cameras at the same time by exploiting the inherent pseudo noise properties of the optical modulation signals. Compared to recent systems based on pure pseudo noise modulation signals, the stochastic measurement error in a single-camera environment is significantly reduced. The basic concept relies on the generation of a three level optical modulation signal that includes two pseudo noise sequences.

Claims

1. An optical time of flight measurement system, comprising:

an illumination source that illuminates an object with optical pseudo noise sequences that have three or more digital levels;

a sensor for detecting the optical pseudo noise sequences from the object and deriving a distance to the object.

2. An optical time of flight measurement system as claimed in claim 1, wherein the illumination source comprises two or more illumination units that generate the three or more digital levels.

3. An optical time of flight measurement system as claimed in claim 1, wherein the sensor comprises a demodulation sensor array.

4. An optical time of flight measurement system as claimed in claim 3, wherein the sensor array comprises a two dimensional array of demodulation pixels.

5. An optical time of flight measurement system as claimed in claim 1, wherein the optical pseudo noise sequences are generated by combining a sequence with a delayed version of the sequence.

6. An optical time of flight measurement system as claimed in claim 5, wherein the sequence is a maximal length sequence.

7. An optical time of flight measurement method, comprising:

illuminating an object with optical pseudo noise sequences that have three or more digital levels; and

detecting the optical pseudo noise sequences from the object and deriving a distance to the object.

8. An optical time of flight measurement method as claimed in claim 7, further comprising driving two or more illumination units that generate the three or more digital levels.

9. An optical time of flight measurement method as claimed in claim 7, further comprising detecting the sequences with a sensor that comprises a demodulation sensor array.

10. An optical time of flight measurement method as claimed in claim 9, wherein the sensor array comprises a two dimensional array of demodulation pixels.

11. An optical time of flight measurement method as claimed in claim 7, further comprising generating the sequences by combining a sequence with a delayed version of the sequence.

12. An optical time of flight measurement method as claimed in claim 11, wherein the sequence is a maximal length sequence.

13. An illumination source for an optical time of flight measurement system, comprising:

a first illumination unit that illuminates an object with a modulated optical signal; and

a second illumination unit that illuminates the object with a modulated optical signal; and

illumination controller that drives the first illumination unit and the second illumination unit to illuminate the object with a modulated optical signal that has three or more digital levels.

14. An illumination method for an optical time of flight measurement system, comprising:

illuminating an object with a first modulated optical signal;

illuminating the object with a second modulated optical signal; and

controlling the timing of the first modulated optical signal and the second modulated optical signal so that the object is illuminated with a modulated optical signal that has three or more digital levels.