Active Pixel Sensor Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The non-uniform threshold voltages of source follower transistors in active pixel sensor circuits lead to non-uniform output currents, causing distortion in images captured by CMOS image sensors.
Innovation Solution
An active pixel sensor circuit is designed with a photosensitive device, storage capacitors, and a source follower transistor, along with reset, charging control, compensation, and signal-reading sub-circuits, which utilize voltage jump compensation to make the output current independent of the source follower transistor's threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source follower transistors are used in active pixel sensor circuits, then photoelectric conversion function is achieved, but non-uniform threshold voltages cause non-uniform output currents leading to image distortion
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the signal reading phase. During the compensation phase, the circuit pre-adjusts the gate voltage of the source follower transistor to counteract the threshold voltage offset, ensuring that the output current becomes independent of threshold voltage variations before actual signal measurement occurs
Solution Approach 2:
The patent changes the operating parameters of the source follower transistor dynamically. By adjusting the gate voltage parameter during different phases (reset, compensation, signal reading), the circuit compensates for threshold voltage variations and maintains uniform output current across different pixels
2Manufacturing precision
If threshold voltage compensation is implemented, then output current uniformity is improved, but circuit complexity increases due to additional control sub-circuits
Solution Approach 1:
The patent achieves multi-functionality by designing control sub-circuits that perform multiple functions: the same control transistors and capacitors are used for both reset operations and threshold voltage compensation. This reduces the need for separate dedicated compensation circuits, thereby limiting the increase in overall circuit complexity
Solution Approach 2:
The patent merges the reset function and compensation function into a unified circuit structure. The reset capacitor and control transistors serve dual purposes: resetting the pixel and compensating for threshold voltage, thus reducing the total component count despite adding compensation functionality
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 effectively eliminates the distortion caused by non-uniform output currents, ensuring that the operating current of the source follower transistor is independent of its threshold voltage, thereby improving image accuracy.
Implementation Method 1
A Complementary Metal-oxide Semiconductor (CMOS) image sensor is capable of transforming the function of pure logic operation into receiving external light rays, converting them into electric energy
Data Source
AI summary
The present disclosure provides an active pixel sensor circuit, a driving method, and an image sensor. The active pixel sensor circuit comprises a photosensitive device, a first storage capacitor, a second storage capacitor and a source follower transistor. The active pixel sensor circuit further comprises a reset sub-circuit, a charging control sub-circuit, a compensation control sub-circuit, a signal-reading control sub-circuit. The charging control sub-circuit controls a second pole of the photosensitive device to be connected to a second terminal of the second storage capacitor during the reset phase and the charging phase, and controls the gate of the source follower transistor to be connected to a second pole of the source follower transistor during the charging phase. The compensation control sub-circuit controls the second terminal of the second storage capacitor to be connected to a second terminal of the first storage capacitor during the reset phase and the compensation phase.