ToF TDC Zoomed Histogram Measurement for High Depth Resolution
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Solution Overview
Problem
Existing time-to-digital converters (TDCs) in time-of-flight (ToF) systems face challenges in achieving high resolution without increasing the number of histogram bins, leading to increased area consumption and power consumption.
Innovation Solution
A TDC system with a pixel-level histogram generation capability that uses a successive approximation method to generate zoomed histograms, reducing the number of bins while maintaining high resolution by incrementally focusing on the region of interest, thereby achieving higher precision with lower area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a counter-based TDC with high clock frequency is used to achieve high time resolution, then measurement precision is improved, but area consumption and power consumption increase
Solution Approach 1:
The patent segments the time measurement process into multiple coarse-to-fine measurement stages. Instead of using a single high-frequency counter, the system divides the measurement into sequential phases that collectively achieve high resolution without requiring a single high-frequency clock, thereby reducing area and power consumption while maintaining measurement precision.
Solution Approach 2:
The patent employs dynamic measurement ranges that adapt to the specific time interval being measured. The system can switch between different measurement modes and ranges based on the actual time duration, allowing high precision measurements to be achieved with lower resource consumption when full resolution is not always required.
2Measurement precision
If a counter-based TDC with high clock frequency is used to achieve high time resolution, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent segments the time measurement process into multiple coarse-to-fine measurement stages. Instead of using a single high-frequency counter, the system divides the measurement into sequential phases that collectively achieve high resolution without requiring a single high-frequency clock, thereby reducing area and power consumption while maintaining measurement precision.
Solution Approach 2:
The patent uses periodic measurement cycles with different resolution levels. The system performs coarse measurements first, then selectively performs fine measurements only when needed, rather than continuously operating at maximum resolution. This periodic, staged approach reduces average power consumption while maintaining the capability for high-precision measurements.
3Measurement precision
If the number of histogram bins is increased to improve depth resolution, then measurement precision is improved, but area consumption increases
Solution Approach 1:
The patent segments the depth measurement range into multiple measurement stages with different resolutions. Instead of using a large number of fine bins across the entire range, the system performs sequential measurements that focus resolution on relevant depth regions, achieving high depth resolution with fewer total bins and reduced area consumption.
Solution Approach 2:
The patent applies different measurement resolutions to different depth regions based on requirements. The system concentrates high-resolution measurement resources on depth regions of interest rather than uniformly distributing resolution across all possible depths, thereby achieving high depth resolution where needed while minimizing overall area consumption.
Data Source
Figure 1~2A
Figure 2B
Figure 2C
AI summary
A method of executing a ToF measurement includes: receiving a first plurality of digital codes from a TDC; generating a coarse histogram from the first plurality of digital codes; detecting a peak coarse bin from the plurality of coarse bins; after receiving the first plurality of digital codes, receiving a second plurality of digital codes from the TDC; and generating a fine histogram from the second plurality of digital codes based on the detected peak coarse bin, where a fine histogram depth range is narrower than a coarse histogram depth range, where a lower fine histogram depth is lower or equal to a lower coarse peak depth, and where a higher fine histogram depth is higher or equal to a higher coarse peak depth.