Event-Driven Pixel Circuit With Passive Difference Detection
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Solution Overview
Problem
Existing event driven pixels consume high power due to DC bias currents, making them unsuitable for battery-operated devices, and suffer from non-uniformity, non-linearity, and inferior noise performance.
Innovation Solution
Incorporating a photosensor, a photocurrent-to-voltage converter, and a passive difference circuit with a source follower buffer, along with a reset control circuit, to reduce power consumption and improve uniformity and dynamic response, while enabling low-latency signal amplification and frame-based readout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC bias currents are used in event driven pixels, then the pixels can operate continuously and detect events, but power consumption increases making them unsuitable for battery-operated devices
Solution Approach 1:
The patent implements periodic action by using a reset control circuit that periodically resets the photosensor node only when events occur, rather than maintaining continuous DC bias currents. The circuit switches between integration mode and reset mode periodically, enabling event-driven operation that consumes power only when necessary, thus resolving the contradiction between continuous operation capability and power consumption.
2Use of energy by moving object
If passive difference detection circuitry is used, then power consumption is reduced, but uniformity and linearity may be compromised
Solution Approach 1:
The patent employs feedback mechanisms through the reset control circuit that monitors the photosensor node voltage and automatically triggers reset operations when threshold levels are reached. This feedback-based control ensures uniform response across pixels and maintains linearity in event detection, while the passive difference detection circuitry keeps power consumption low by avoiding active amplification stages.
3Use of energy by moving object
If reset control circuits are added to manage reset operations, then power consumption is optimized, but device complexity increases
Solution Approach 1:
The patent merges the reset control functionality with the existing pixel circuit architecture by integrating the reset control circuit into the pixel structure. The reset control circuit shares control signals and timing mechanisms with other pixel operations, combining multiple functions into a unified design that optimizes power consumption without proportionally increasing complexity.
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
The solution reduces power consumption, enhances uniformity and linearity, and improves noise performance, making the event driven pixels suitable for battery-operated devices with prolonged battery life and high-speed capabilities.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
Low power event driven pixels with passive difference detection circuit (and reset control circuits for the same) are disclosed herein. In one embodiment, an event driven pixel comprises a photosensor; a photocurrent-to-voltage converter, and a difference circuit. The difference circuit includes a source follower transistor and a switched-capacitor filter having an input coupled to the photocurrent-to-voltage converter and an output coupled to a gate of the source follower transistor. The switched-capacitor filter includes a first capacitor coupled between the input and the output of the switched-capacitor filter, a second capacitor having a first plate coupled to the output of the switched-capacitor filter, and a reset transistor coupled between a reference voltage and the output of the switched-capacitor filter. The difference circuit is configured generate a difference signal that is indicative of whether the event driven pixel has detected an event in an external scene.