Image Sensor Charge Pump for High Negative Bias and Low Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing image sensors face challenges in improving dark current characteristics, which are essential for enhancing performance and reducing noise in image capture.
Innovation Solution
A charge pump circuit is designed to generate a high negative voltage, which is applied to the isolation layer of the active pixel sensor array, thereby improving the dark current characteristics of the image sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional charge pump circuits are used in image sensors, then the circuit can generate voltages outside the supply potential range, but the dark current characteristics deteriorate
Solution Approach 1:
The charge pump circuit is divided into multiple stages (first charge pump circuit, second charge pump circuit, third charge pump circuit) that generate different voltage levels sequentially. Each stage operates independently to generate specific voltages (VDD, -VDD, -2VDD) without interfering with each other, thereby reducing dark current while maintaining voltage multiplication capability
Solution Approach 2:
Different regions of the pixel array are assigned different potential levels (first region at VDD, second region at -VDD, third region at -2VDD). This local differentiation of electrical properties allows the circuit to generate high voltages in specific regions without causing uniform dark current increase across the entire sensor
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 implementation of the charge pump circuit effectively reduces dark current and enhances the performance of the image sensor by applying a high negative voltage to the isolation layer, leading to improved image quality.
Implementation Method 1
charge pump circuit capable of outputting a high negative voltage
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A charge pump circuit includes a first pump unit and a second pump unit. The first pump unit includes a first capacitor and a first transistor, and generates a first node voltage by using a clock signal. The second pump unit includes a second capacitor, a second transistor, and a third transistor, and generates a negative output voltage by using the first node voltage. The clock signal and the first node voltage are each toggled between a low-level voltage and a high-level voltage. A magnitude of an absolute value of the negative output voltage is greater than a magnitude of an absolute value of the high-level voltage of the clock signal. A body of the third transistor is electrically isolated from a body of the second transistor.