Event-Driven Pixel Difference Circuitry for Low-Power Image Sensing
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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 they suffer from non-uniformity, non-linearity, and poor noise performance.
Innovation Solution
The implementation of low power event driven pixels with active difference detection circuitry and reset control circuits, which include a photosensor, a photocurrent-to-voltage converter, and a difference circuit with signal amplification at the output stage, enabling power savings and improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC bias currents are used in event driven pixels, then event detection functionality is maintained, but power consumption increases
Solution Approach 1:
The patent implements periodic reset pulses instead of continuous DC bias currents. The reset control circuit generates periodic reset signals that periodically charge the reset capacitor, maintaining event detection functionality while consuming power only during these periodic intervals rather than continuously, thereby resolving the contradiction between maintaining functionality and reducing power consumption
Solution Approach 2:
The patent extracts and eliminates the continuous DC bias current component from the pixel circuit. By using a reset capacitor charged periodically by control circuits rather than continuous DC bias, the harmful continuous power consumption is removed while the useful event detection function is preserved through periodic sampling
2Ease of manufacture
If simple pixel circuits are used, then manufacturing is easier, but non-uniformity and non-linearity increase
Solution Approach 1:
The patent introduces a reset capacitor and periodic reset control that changes the operating parameters of the pixel circuit. This allows for better linearity and uniformity in the charge transfer process by controlling the reset timing and voltage levels, improving manufacturing precision without significantly complicating the fabrication process
Solution Approach 2:
The reset control circuits provide feedback control by monitoring and adjusting the reset pulse timing and amplitude. This feedback mechanism ensures consistent charge transfer across pixels, reducing non-uniformity and improving linearity while maintaining manufacturing feasibility
3Reliability
If DC bias currents are used in event driven pixels, then event detection is enabled, but noise performance deteriorates
Solution Approach 1:
By replacing continuous DC bias with periodic reset pulses, the patent eliminates the continuous noise floor associated with DC operation. The periodic sampling approach only measures signals at discrete moments when reset pulses are applied, thereby avoiding the accumulation of thermal noise that occurs with continuous DC bias currents
Solution Approach 2:
The patent converts the potential harm of needing continuous bias current into a benefit by using periodic pulses. The brief periodic charging moments provide sufficient signal levels for detection while the intervals between pulses allow noise to settle, effectively using the periodic nature to suppress noise while maintaining detection capability
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 solution reduces power consumption, decreases non-uniformity and non-linearity, and improves noise performance, leading to more efficient and accurate event detection in image sensors.
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 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 coupled to the photosensor; and a difference circuit coupled to the photocurrent-to-voltage converter. The difference circuit includes a source follower transistor and is configured to generate a signal at a gate of the source follower transistor that is based on a voltage output from the photocurrent-to-voltage converter. The difference circuit is further configured to output a difference signal in response to assertion of a row select signal. The event driven pixel can further include a reset control circuit coupled to the difference circuit and configured to initialize the difference circuit, and to reset the difference circuit when the difference signal output from the event driven pixel indicates a change in the voltage greater than a threshold amount.