Gray-Coded TDC Timestamp Latching for Low-Power ToF Histograms
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Solution Overview
Problem
Time-of-flight (ToF) systems face challenges in achieving high time resolution and power efficiency while minimizing routing congestion, particularly in applications requiring precise timestamping and histogram generation for events such as in proximity sensors and LIDAR systems.
Innovation Solution
The implementation of a gray-coded time reference system, where a gray-coded time reference is latched into a memory upon event reception and used to update a ToF histogram, allowing for efficient power usage and improved routing by minimizing clock edges and preventing incorrect code latching, thereby enhancing resolution without increased power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional binary-coded time reference is used in TDC, then the system can achieve time measurement functionality, but routing congestion increases and power consumption rises due to multiple clock edges
Solution Approach 1:
The patent extracts only the necessary timing information by using a gray-coded time reference that updates only one bit at a time, removing the need for multiple clock edges required by binary-coded references. This reduces routing complexity while maintaining time measurement capability.
Solution Approach 2:
The patent changes the encoding parameter of the time reference from binary code to gray code. This parameter change ensures that only one bit changes between consecutive time references, reducing the number of clock edges from multiple (in binary) to single (in gray), thereby reducing routing congestion and power consumption.
2Measurement precision
If a conventional binary-coded time reference is used in TDC, then the system can achieve time measurement functionality, but power consumption increases due to multiple clock edges
Solution Approach 1:
The patent changes the encoding parameter of the time reference from binary code to gray code. This parameter change ensures that only one bit changes between consecutive time references, reducing the number of clock edges from multiple (in binary) to single (in gray), thereby reducing routing congestion and power consumption.
Solution Approach 2:
The patent implements periodic updating of the time reference using gray code, where only one bit changes at each time step. This periodic single-bit update reduces the frequency of clock edge transitions compared to binary coding, leading to lower dynamic power consumption in the TDC circuit.
3Measurement precision
If a conventional binary-coded time reference is used in TDC, then the system can achieve time measurement functionality, but incorrect code latching occurs due to simultaneous bit changes
Solution Approach 1:
The patent changes the encoding parameter of the time reference from binary code to gray code. This parameter change ensures that only one bit changes between consecutive time references, eliminating the simultaneous multi-bit transitions inherent in binary coding. This prevents metastability and incorrect latching, improving reliability.
Solution Approach 2:
The patent uses gray code encoding as a preventive measure against incorrect latching. By designing the time reference to change only one bit at a time, the system beforehand prevents the occurrence of metastability and latching errors that would otherwise occur with simultaneous multi-bit changes in binary-coded references.
Data Source
AI summary
In an embodiment, a method includes: providing a gray-coded time reference to a time-to-digital converter (TDC); receiving an event from an event signal; latching the gray-coded time reference into a memory upon reception of the event signal; and updating a time-of-flight (ToF) histogram based on the latched gray-coded time reference.