Image Sensor Reference Signal Correction for Voltage Fluctuation
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Solution Overview
Problem
Conventional image sensors face a challenge in maintaining image quality due to fluctuations in negative voltage power source output, which affect the dynamic range and noise susceptibility, and downsizing is hindered by the need for high-capacity capacitors to stabilize these fluctuations.
Innovation Solution
An image sensor design that includes an electric charge holding unit, an image signal output unit controlled by control signals, a reset unit that transmits voltage fluctuations, a reference signal generation and correction unit, and an analog-to-digital conversion unit that corrects the reference signal based on voltage fluctuations, allowing for stable image signal processing without the need for high-capacity capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-capacity capacitor is added to the output of the negative power source to reduce voltage fluctuation, then the stability of the power source output is improved, but the device size increases and downsizing becomes difficult
Solution Approach 1:
The invention extracts the capacitor from the power source output side and relocates it to the pixel circuit side, specifically connecting it to the reset unit. This extraction allows the main power source to remain small while achieving voltage stabilization through the localized capacitor in the pixel circuit, thereby resolving the contradiction between stability and device size.
Solution Approach 2:
The invention applies local quality by placing a capacitor specifically in the reset unit of the pixel circuit rather than at the power source output. This localized approach provides voltage fluctuation compensation exactly where needed (in the pixel circuit) without requiring a large capacitor throughout the entire system, thus achieving stability improvement without increasing overall device size.
2Use of energy by moving object
If the power source voltage is reduced to lower power consumption, then energy efficiency is improved, but the dynamic range of the photoelectric conversion element becomes narrower and noise susceptibility increases
Solution Approach 1:
The invention applies preliminary action by resetting the photoelectric conversion element before the actual photoelectric conversion process using the reset unit. This preliminary reset action prepares the element for optimal operation at lower voltages, enabling the system to maintain good dynamic range and noise performance even when operating at reduced power source voltages for lower power consumption.
Solution Approach 2:
The invention implements feedback through the reset unit that uses a control signal to adjust the reset operation based on the operating conditions. This feedback mechanism allows the pixel circuit to adapt to lower voltage conditions, maintaining reliable photoelectric conversion performance while operating at reduced power consumption levels.
3Reliability
If a negative voltage power source is used to widen dynamic range and reduce noise effect, then photoelectric conversion performance is improved, but voltage fluctuations from load changes affect image signals through parasitic capacitance
Solution Approach 1:
The invention introduces an intermediary element - the capacitor connected to the reset unit - that mediates between the negative power source and the photoelectric conversion element. This intermediary capacitor absorbs voltage fluctuations from the power source, preventing them from being transmitted through the parasitic capacitance of the reset unit to the image signal, thus maintaining photoelectric conversion performance while eliminating image signal fluctuation.
Solution Approach 2:
The invention extracts the voltage fluctuation problem from the power source output and relocates the fluctuation absorption function to the reset unit capacitor. This extraction allows the negative power source to continue providing the beneficial negative voltage for wide dynamic range and low noise, while the separate capacitor in the reset unit handles the harmful voltage fluctuations, preventing them from affecting the image signal.
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 effectively reduces image signal fluctuations caused by negative voltage power source variations, preventing a decline in image quality while enabling the downsizing of image sensors.
Implementation Method 1
a complementary metal oxide semiconductor (CMOS)-type image sensor has been conventionally used. The image sensor includes a plurality of pixels each including a photoelectric conversion element that generates an image signal corresponding to emitted light.
Implementation Method 2
By adding a high-capacity capacitor to an output of the negative power source, a fluctuation in an output voltage can be reduced.
Data Source
AI summary
An image signal output unit is controlled in accordance with a first control signal indicating either voltage state of an on voltage for causing a conductive state and an off voltage having a polarity different from that of the on voltage, and outputs an analog image signal corresponding to the electric charge held by an electric charge holding unit in the conductive state. A reset unit is controlled in accordance with a second control signal indicating either voltage state of the on voltage and the off voltage, resets the electric charge holding unit in the conductive state, transmits a fluctuation in the off voltage to the electric charge holding unit, and fluctuates the analog image signal. A reference signal generation unit generates a reference signal being a signal serving as a reference used when conversion from an analog image signal output from the image signal output unit into a digital image signal is performed. A reference signal correction unit corrects the generated reference signal in accordance with the fluctuation in the off voltage. An analog-to-digital conversion unit performs the conversion on the basis of the corrected reference signal.