Depth Map Sensor Bin Rotation for ToF Accuracy
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Solution Overview
Problem
Current time-of-flight (ToF) cameras with single photon avalanche diodes (SPADs) face inaccuracies in distance measurements due to non-uniform time-sampling of phase-shifted clock signals, leading to disturbances in the detection of returned waveforms.
Innovation Solution
A depth map sensor design that includes a first array of pixels with phase-shifted clock signals applied during different periods and selection mechanisms, and a second array with distinct phase-shifted clock signal application durations, allowing for cyclic circular shifts to mitigate signal discrepancies and improve time-domain averaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If phase-shifted clock signals are applied to pixel circuits with fixed time windows for event accumulation, then the circuit operation is simplified, but non-uniformity in time-sampling occurs leading to degraded distance measurement accuracy
Solution Approach 1:
The patent applies dynamics by making the time window assignment dynamic rather than fixed. Each pixel circuit is assigned a specific time window that shifts across multiple periods, allowing the system to adapt to non-uniform sampling conditions. This dynamic reassignment ensures that over time, all time windows are uniformly sampled, correcting the non-uniformity issue while maintaining circuit simplicity.
Solution Approach 2:
The patent implements periodic action by cycling through different time window assignments for each pixel circuit over multiple periods. Each period, the time window index is incremented, creating a periodic rotation of sampling windows. This periodic reassignment ensures uniform coverage of all time windows across multiple cycles, eliminating the non-uniform sampling bias that degrades measurement accuracy.
2Ease of manufacture
If time windows are fixed for event accumulation in each pixel circuit, then the implementation is straightforward, but non-uniform time-sampling disturbs phase detection accuracy
Solution Approach 1:
The system transitions from static fixed time windows to dynamic rotating time window assignments. Each pixel circuit's time window index is updated based on the current period, creating a dynamic sampling scheme. This dynamic approach maintains implementation simplicity while correcting the non-uniform sampling that would otherwise distort phase detection accuracy.
Solution Approach 2:
The patent changes the parameter of time window assignment from fixed to variable based on the period number. By modifying the time window index as a function of the period, the system creates uniform sampling distribution across all time windows. This parameter change eliminates the non-uniformity that causes phase detection errors while keeping the implementation straightforward.
3Device complexity
If all pixel circuits use the same time window assignment, then the control logic is minimized, but non-uniform sampling patterns degrade depth map accuracy
Solution Approach 1:
The patent introduces dynamic time window assignment where each pixel circuit's assigned window changes based on the current period. This dynamic scheme ensures that over time, all time windows are sampled uniformly across the pixel array. The control logic remains relatively simple by using a counter that increments with each period, but this simple mechanism achieves uniform sampling that improves depth map accuracy.
Solution Approach 2:
The system employs periodic action by cycling through time window assignments in a rotating manner across multiple periods. Each period, the time window index is incremented for all pixel circuits, creating a periodic rotation that ensures uniform sampling coverage. This periodic mechanism maintains minimal control logic complexity while achieving the uniform sampling necessary for accurate depth mapping.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the accuracy of distance measurements by averaging out discrepancies in phase-shifted clock signals, leading to improved precision in depth map sensing.
Implementation Method 1
an array of SPADs for detecting the return signal
Implementation Method 2
a laser source such as a vertical-cavity surface-emitting laser (VCSEL) that emits, into an image scene, optical pulses
Data Source
AI summary
A depth map sensor includes a first array of first pixels, each first pixel having a first photodetector associated with a pixel circuit that comprises a plurality of first bins for accumulating events. A clock source is configured to generate a plurality of phase-shifted clock signals. A first circuit has a plurality of first output lines coupled to the first array of first pixels. The first circuit is configured to receive the plurality of phase-shifted clock signals. The first circuit includes a first block and a second block. The first block is configured to propagate the plurality of phase-shifted clock signals to the second block during a first period determined by a first enable signal and the second block configured to select to which of the plurality of first output lines each of the plurality of phase-shifted clock signals is applied.