ToF Ranging

ToF Ranging

Recent advances in semiconductor technology have allowed the realization of time-of-flight (ToF) cameras in 3D imaging. Time-of-flight (ToF) cameras have many advantages over the other conventional 3D imaging schemes and have gained popularity recently, however, they have still not been adopted in mainstream of 3D imaging applications, largely due to the lack of a robust algorithm in phase delay measurement that provides competitive fine-depth resolution. The principle of phase delay measurement of typical lock-in ToF is based on the simple two-phase I/Q correlations or four-phase correlations that have 90° phase delay from each other, which is commonly known as “four-bucket” algorithm.
As an application of the ZF transform to lock-in ToF ranging, correlations of odd-numbered N-phase are employed in ZF ToF Ranging. The two-phase orthogonal signal of sine and cosine is synthesized from the output signals of N-phase correlators by the ZF transform. The ZF ToF Ranging significantly improves the depth resolution as well as its linearity, compared with those by the typically used four-bucket algorithm.

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Phase-Delay Measurement Algorithm: Typical ToF vs. ZF ToF Ranging

  • Typical ToF Ranging
  • ZF ToF Ranging
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Harmonic Distortions are Removed by the ZF Transform

  • Harmonic Components are Removed from the Sensed Signals.
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Phase-Delay Measurement Error Comparison: Typical ToF vs. ZF ToF Ranging

  • Measurement Error over Phase-Delay (Sweeping over 180°)

Types

Typical TOF 4-Phase

ZF TOF 3-Phase

ZF TOF 5-Phase

ZF TOF 9-Phase

Measurement at
Phase-Delay at 25.0°

21.06°

23.80°

25.23°

25.02°

Measurement Error
(degree °)

3.94°

1.20°

-0.23°

-0.015°

Percentage Error (%)

15.8

4.8

0.9

0.06

Improvement Factor
over the Typical One

NA

3.3

17.5

259

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Linearity and Scalability

  • Measured Phase-Delay Variation is Linear with the Distance Variation
  • Ranging Depth is Adjusted by the Number of Correlators Employed

Linearity Comparison

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Applications

  • ZF Radar Sensor
    -Intermittent Signal Radar is Feasible as well as Conventional Pulse or SW Radar.
    -Improved Accuracy for the Phase Synthesis Radar
    -Applicable to Ultra-Sonic Radar
  • Smart Proximity Sensor
    -Proximity Sensors Detect an Object without Touching it.
    -ZF ToF Technology can Detect the Distance very Precisely
  • 3D Imaging
    -Phase-Delay Varies Linearly with Distance Variation over all 360°.
    -In Combination with the R,G,B Image Sensors, Smoother 3D Image is Constructed
  • Electronic Ruler
  • Direction Finder
  • Synchronization among Mobile Base Stations