Coupled Ring Oscillator Arrays for Low-Noise ToF TDC Timing
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Solution Overview
Problem
Time-of-flight image sensor devices face challenges in providing high accuracy and precision in timing information over the sensor pixel area due to non-linearity, jitter, and high power consumption, particularly in 3D imaging applications where oscillators' phase noise and process-voltage-temperature variations affect the performance of time-to-digital converters.
Innovation Solution
An oscillator arrangement for time-to-digital converters is implemented, where multiple ring oscillators are arranged in an array with coupling units between them to synchronize oscillation at a fundamental frequency, reducing phase noise and power consumption while maintaining robust synchronization and low dependency on temperature and voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single time-to-digital converter is used together with a distribution network, then timing information can be provided to multiple pixels, but high power consumption and non-linearity occur due to routing multiple phases of an oscillator over the sensor area
Solution Approach 1:
The patent divides the system into multiple independent time-to-digital converters, each with its own local oscillator, rather than using a single centralized TDC with distribution network. This segmentation eliminates the need for complex phase distribution routing and reduces power consumption associated with distributing timing signals across the sensor area.
Solution Approach 2:
Each pixel region is equipped with its own local oscillator and TDC, providing timing signals locally without requiring long-distance distribution. This local quality approach reduces the power consumption and non-linearity issues associated with routing oscillator phases over large sensor areas.
2Use of energy by moving object
If one time-to-digital converter per pixel is used, then power consumption is reduced in photon-starved applications, but the converters are highly susceptible to process-voltage-temperature variations, jitter accumulations and non-linearity when operating in open loop independently
Solution Approach 1:
The patent merges multiple independent oscillators through coupling units that synchronize them at a fundamental frequency. This combining approach maintains the low power consumption of individual oscillators while improving reliability by reducing susceptibility to PVT variations through mutual synchronization and noise averaging.
Solution Approach 2:
The coupling units create a feedback mechanism where oscillators monitor and adjust to each other's timing, synchronizing at a fundamental frequency. This feedback reduces jitter accumulations and non-linearity by continuously correcting deviations caused by process-voltage-temperature variations.
3Measurement precision
If multiple oscillator coupling is implemented, then phase noise is significantly reduced, but device complexity increases
Solution Approach 1:
The oscillator array is segmented into multiple independent units that are coupled through simple coupling units. This segmentation allows phase noise reduction through multiple oscillators while keeping each unit's complexity manageable and avoiding the need for a single complex centralized oscillator.
Data Source
AI summary
An oscillator arrangement for time-to-digital converters for a 3D image sensor device includes a plurality of oscillators arranged as an array each oscillator being associated to one time-to-digital converter, and at least one coupling unit respectively arranged between at least two of the oscillators, so that oscillation in the at least two oscillators at a fundamental frequency is synchronized between the at least two coupled oscillators.