Readout Circuit Biasing for Image Sensor Dynamic Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The effective voltage range of the floating diffusion node in pixel circuits of image sensors is limited by the output voltage swing of readout circuits, leading to signal truncation and image distortion.
Innovation Solution
A readout circuit with a biasing circuit including a cascode transistor and a biasing transistor, coupled to a negative voltage, which provides a signal readout function with a high dynamic range by ensuring a wide output voltage swing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the readout circuit uses a conventional biasing configuration, then the circuit structure is simple, but the output voltage swing is limited causing signal truncation and image distortion
Solution Approach 1:
The biasing circuit is segmented into a conventional biasing transistor and a cascode transistor connected in series. This segmentation allows the cascode transistor to extend the output voltage swing range while the biasing transistor maintains the basic biasing function, thereby resolving the contradiction between simple structure and accurate signal readout.
Solution Approach 2:
The cascode transistor is added in the vertical dimension of the circuit topology, stacking above the biasing transistor. This dimensional addition extends the voltage swing range without significantly increasing lateral circuit complexity, enabling high dynamic range readout while maintaining relatively simple circuit layout.
2Adaptability or versatility
If the readout circuit is coupled to negative voltage, then the dynamic range is enhanced, but the device complexity increases
Solution Approach 1:
The cascode transistor serves multiple functions: it extends the output voltage swing range, enables coupling to negative voltage for high dynamic range, and maintains signal integrity. This multi-functionality achieves enhanced adaptability without proportionally increasing device complexity.
Data Source
AI summary
A readout circuit is provided. The readout circuit is coupled to a pixel circuit for reading out signals from the pixel circuit. The readout circuit includes a biasing circuit. The biasing circuit includes a cascode transistor and a biasing transistor. A first terminal of the cascode transistor is coupled to an output terminal of the biasing circuit and the pixel circuit. A second terminal of the cascode transistor is coupled to a first terminal of the biasing transistor. A second terminal of the biasing transistor is coupled to a negative voltage.