Split Bus Routing for DTOF Sensor Signal Integrity
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Solution Overview
Problem
DTOF image sensors face challenges in routing signals between SPADs and TDCs, requiring precise timing and high-frequency data handling, which affects power consumption and area density, especially in high-resolution sensors with hundreds or thousands of pixels.
Innovation Solution
The implementation of a split bus routing system where half of the SPADs in a subset are routed to top TDCs and the other half to bottom TDCs, reducing the number and length of routes, and using a shared bus for event signals and data readout, while maintaining timing precision and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional routing system is used to connect all SPADs to TDCs, then the sensor can capture images, but the routing complexity and area increase significantly in high-resolution sensors
Solution Approach 1:
The patent segments the pixel array into multiple subsets (first subset and second subset) and routes them to different TDC groups (first plurality of TDCs and second plurality of TDCs) through separate routing buses. This segmentation reduces the routing complexity by dividing the large routing task into smaller, manageable segments, allowing high-resolution sensors to maintain timing precision without excessive routing complexity.
Solution Approach 2:
The patent introduces a shared bus dimension that allows both event signals from SPADs and data readout to traverse the same physical routing path. By utilizing the time dimension (different signal types at different times) rather than requiring separate spatial paths, the system reduces routing area and complexity while maintaining signal integrity and timing precision.
2Reliability
If separate routing paths are provided for event signals and data readout, then signal integrity is maintained, but the routing area and power consumption increase
Solution Approach 1:
The patent implements a shared bus that serves multiple functions: it carries event signals from SPADs to TDCs during one operational phase and carries data readout in another phase. This multi-functionality allows the same physical routing infrastructure to handle different signal types, significantly reducing the total routing area required while maintaining signal integrity through proper signal timing and isolation.
Solution Approach 2:
The system uses periodic action by sequentially transmitting different types of signals (event signals first, then data readout) through the shared bus in different time periods. This time-division multiplexing allows the shared routing path to handle multiple functions without signal interference, maintaining reliability while reducing area requirements compared to dedicated separate paths.
3Measurement precision
If more pixels are added to increase resolution, then image quality improves, but power consumption increases due to routing requirements
Solution Approach 1:
The patent merges the routing functions for event signals and data readout into a single shared bus infrastructure. This merging reduces the total number of routing traces and interconnects required, thereby reducing the power consumption associated with signal transmission and routing control. The shared bus is activated only when needed, optimizing power usage while supporting high-resolution pixel arrays.
Data Source
Figure 1~2
Figure 3
Figure 4A
AI summary
A ToF sensor includes an array of pixels having first and second subsets of pixels, first and second pluralities of TDCs, a routing bus having first and second pluralities of bus drivers, and a controller configured to: when the first subset of pixels is active and the second subset of pixels is not active, control the first plurality of bus drivers to route events from half of the pixels of the first subset to the first plurality of TDCs and control the first and second pluralities of bus drivers to route events from the other half of the pixels of the first subset to the second plurality of TDCs, and when the first subset of pixels is not active and the second subset of pixels is active, control the first plurality of bus drivers to route events from the second subset of pixels to the first plurality of TDCs.