Multi-Mode SPAD Readout Circuit for Compact IoT Sensors
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Solution Overview
Problem
In miniature size applications such as scribe line testing and Internet of Things, Single Photon Avalanche Diodes (SPAD) require a novel architecture for readout circuits that can handle multiple applications like photon counting, time-of-flight, and after pulsing modes within a limited pin count and chip area.
Innovation Solution
The proposed image sensor system incorporates a timing control circuit and readout circuits with clamping, logic, ring oscillator, multiplexing, and counting circuits, allowing each diode to selectively operate in photon counting, time-of-flight, and after pulsing modes by generating control signals and counting photons or time periods based on input signals and clock pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate readout circuits are used for different SPAD applications (photon counting, time-of-flight, after pulsing), then each application can be optimized, but the pin count and chip area increase significantly
Solution Approach 1:
The patent implements a universal readout circuit architecture that can operate in multiple modes (photon counting, time-of-flight, after pulsing) by using a single integrated circuit design. The circuit includes mode selection logic and configurable components that allow it to adapt its functionality based on the desired application, eliminating the need for separate dedicated circuits for each SPAD application type.
Solution Approach 2:
The patent combines multiple previously separate readout circuit functions into a single integrated circuit. By merging the photon counting logic, time-of-flight measurement capabilities, and after pulsing detection functions into one unified circuit block, the design reduces the total number of circuits required while maintaining all necessary functionalities through shared hardware resources and multiplexing techniques.
2Reliability
If multiple dedicated readout circuits are implemented for different modes, then each mode operates independently, but the pin count increases
Solution Approach 1:
The readout circuit is designed as a universal multi-functional unit that can perform photon counting, time-of-flight measurement, and after pulsing detection through reconfigurable logic. This single circuit replaces multiple dedicated circuits, significantly reducing the pin count required for interfacing while maintaining the ability to operate independently in each mode through internal mode selection and control logic.
3Area of stationary object
If a novel unified readout circuit architecture is used, then chip area is reduced, but the circuit design complexity increases
Solution Approach 1:
The unified readout circuit is segmented into distinct functional modules, each handling specific tasks (photon detection, timing measurement, mode control, signal processing). This modular segmentation allows the complex functionality to be organized into manageable units that can be independently designed and tested, reducing the overall design complexity despite the integrated nature of the circuit.
Solution Approach 2:
The circuit employs dynamic reconfiguration capabilities where the same hardware resources are dynamically allocated to different functions based on the operating mode. This dynamic approach allows a single circuit to perform multiple roles by changing its internal configuration and signal routing, reducing the need for static dedicated circuits for each function.
4Adaptability or versatility
If separate circuits are used for each SPAD application, then functionality is optimized, but power consumption increases
Solution Approach 1:
The patent merges multiple application-specific circuits into a single power-efficient readout circuit. By combining the photon counting, time-of-flight, and after pulsing detection functions into one integrated circuit, the total power consumption is reduced due to shared power supply, common signal processing pathways, and the ability to power down unused functional blocks when not in use.
Solution Approach 2:
The universal readout circuit is designed to perform multiple functions using shared hardware resources, which reduces redundant power consumption. The circuit can dynamically activate only the necessary functional blocks for the current application, minimizing power usage while maintaining full functionality across all supported modes.
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 architecture reduces the number of readout circuits needed, minimizing chip area and power consumption while enabling efficient operation across different modes, thus addressing the challenge of limited space and complexity in miniature applications.
Implementation Method 1
an image sensor includes a plurality of diodes, and each of the plurality of diodes outputs a sensing current when a photon is detected
Data Source
AI summary
An image sensor system, including: an image sensor, a readout circuit, and a timing control circuit. The image sensor includes a plurality of diodes, and one of the plurality of diodes outputs a sensing current when a photon is detected. The readout circuit is coupled to the image sensor and arranged to selectively operate in at least a first mode and a second mode. The timing control circuit is coupled to the readout circuit and is arranged to determine if a coding condition is fit according to an input signal and generate a control signal when the coding condition is fit, wherein the input signal input signal includes a plurality of bits serially input to the timing control circuit, and each bit of the plurality of bits corresponds to each pulse of a clock signal respectively.