Pixel Array Variable Impedance Low Voltage Operation
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Solution Overview
Problem
CMOS image sensors face challenges in reducing the supply voltage while maintaining correct operation of the voltage follower transistor, which limits the energy efficiency and range of pixel values that can be read.
Innovation Solution
A pixel array with a variable impedance coupling the voltage output rail to a supply rail, controlled by a differential amplifier and a current source, allowing for adjustable impedance based on the voltage level, enabling reduced supply voltage operation without compromising read voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the supply voltage of the pixel array is reduced to lower energy consumption, then energy efficiency is improved, but the voltage follower transistor cannot operate correctly and the read voltage range is limited
Solution Approach 1:
The patent applies dynamics by making the impedance of the impedance element adjustable rather than fixed. The impedance value is dynamically adapted based on the voltage level on the further voltage rail, allowing the system to optimize performance for low supply voltage operation while maintaining sufficient read voltage range. This is achieved through control circuitry that adjusts the impedance element's resistance or conductance in response to detected voltage conditions.
Solution Approach 2:
The patent changes the impedance parameter of the impedance element to resolve the contradiction. By adjusting the impedance value, the system can maintain proper voltage follower transistor operation at reduced supply voltages. The impedance parameter is modified based on the voltage level detected on the further voltage rail, enabling correct transistor operation while operating from lower supply voltage sources.
2Power
If the supply voltage is reduced, then power consumption decreases, but the range of pixel values that can be read is limited
Solution Approach 1:
The patent uses a dynamically adjustable impedance element that adapts its impedance value based on the voltage level on the further voltage rail. This dynamic adjustment allows the system to extend the readable voltage range even when operating from reduced supply voltages, thereby maintaining adaptability while reducing power consumption.
Solution Approach 2:
The patent implements feedback control where the impedance element is controlled based on the detected voltage level on the further voltage rail. This feedback mechanism allows the system to automatically adjust the impedance to maintain sufficient read voltage range across varying supply voltage conditions, ensuring the full range of pixel values can be read despite lower power consumption operation.
Data Source
AI summary
A pixel array including a first pixel having a first transistor having: its control node coupled to a first photodiode; a first of its main conducting nodes coupled to a voltage output rail; and a second of its main conducting nodes coupled to a further voltage rail; a variable impedance coupling the voltage output rail to a first supply rail of the pixel array; and a current source coupling the further voltage rail to a second supply rail of the pixel array, wherein the variable impedance is controlled based on the voltage level on the further voltage rail.