TDC Sharing in CMOS Distance Sensors
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Solution Overview
Problem
Existing CMOS distance measurement methods have a low filling factor due to the complexity of time-to-digital converters (TDCs), which restricts the parallel function of pixels and results in inefficient distance determination, especially in applications like ADAS and automated driving where high-resolution and real-time detection are critical.
Innovation Solution
The solution involves sharing a TDC among several pixels, using a wired-OR connection for signal lines and a counter system to store time values, allowing for efficient time measurement and allocation without increasing the number of vertical signal lines, thereby improving the filling factor and reducing wiring complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a TDC is integrated in every pixel for parallel run time measurements, then measurement precision and reliability are improved, but device complexity increases and filling factor decreases to 1-3.5%
Solution Approach 1:
Multiple pixels share a common TDC circuit instead of each pixel having its own dedicated TDC. The TDC is placed in a shared region accessible by multiple pixels through vertical signal lines, reducing overall device complexity while maintaining parallel measurement capability through time-multiplexed access.
Solution Approach 2:
The TDC circuit is moved from the pixel plane to a shared region below the pixel array, utilizing the vertical dimension for signal access. This spatial reorganization allows multiple pixels to share the same TDC resource without interfering with the light-sensitive pixel area, thereby improving filling factor.
2Area of stationary object
If one TDC is shared among several pixels to improve filling factor, then filling factor increases to over 50%, but the completely parallel function of pixels is restricted
Solution Approach 1:
The system performs preliminary actions by pre-configuring time slots and establishing time-multiplexed access schemes before measurements begin. This allows the shared TDC to efficiently serve multiple pixels with minimal contention, maintaining high productivity while enabling pixel sharing.
Solution Approach 2:
The system dynamically allocates the shared TDC resource to different pixels based on measurement requirements and timing. By implementing dynamic time-multiplexed access, the system optimizes the balance between filling factor improvement and maintaining parallel measurement efficiency.
3Area of stationary object
If TDCs are placed outside the light-sensitive sensor region to improve filling factor, then filling factor increases, but wiring complexity increases due to additional signal lines
Solution Approach 1:
The vertical signal lines are designed to serve dual purposes: they provide readout signals from pixels during normal operation and simultaneously provide access paths for shared TDC resources. This multi-functionality reduces the need for additional dedicated signal lines, minimizing wiring complexity while maintaining high filling factor.
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
This approach enhances the filling factor of CMOS sensors from 3% to over 50%, enabling more efficient and reliable high-resolution distance measurements in real-time, particularly suitable for automotive applications by reducing the number of vertical signal lines and allowing for larger SPAD matrices integration.
Implementation Method 1
Each of the one or several optical detectors comprises a single-photon avalanche diode
Implementation Method 2
the run time of the infrared laser light emitted by an active radiation source and reflected by a target object is measured. This is referred to as LIDAR (light detection and ranging)
Data Source
AI summary
An apparatus for distance measurement, having one or several optical detector modules and a readout module is provided. The optical detector modules each have a plurality of optical detector elements having one or several optical detectors and a counter indicating a count value, the optical detector elements each being in an active state or an inactive state. Each optical detector module has a timer element configured to determine a current time value and configured to continuously update the current time value, and a memory element for storing a plurality of time values stored. The readout module is configured to determine and output, for each detector module of the one or several optical detector modules, at least for each optical detector element of the optical detector elements of this optical detector module, which is in an inactive state, a time value for this optical detector element in dependence on the count value of the counter of this optical detector element and on the plurality of time values stored.