Zero-Biased Multiplexer CTIA Pixel Circuit Design
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Solution Overview
Problem
Existing CTIA pixel circuits face issues with leakage current and large circuit area, which hinder the achievement of high conversion gain and linear zero-biased operation, especially when used in high-density image sensor arrays.
Innovation Solution
The implementation of a zero-biased multiplexer with a reset switch network comprising multiple transistors, which minimizes leakage current and reduces the per-pixel area by using a source-body tie and grounding body terminals of certain transistors, thereby reducing noise and dynamic range consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CTIA pixel circuits are used, then charge transfer is enabled, but leakage current occurs and conversion gain is reduced
Solution Approach 1:
The patent changes the biasing parameter of the multiplexer from conventional biased operation to zero-biased operation. By setting the multiplexer bias voltage to zero (Vmux = 0), the patent eliminates leakage current paths while maintaining charge transfer functionality, thereby improving conversion gain and linearity
Solution Approach 2:
The patent uses a dummy photodiode that copies the structure and characteristics of real photodiodes but does not generate signal charge. This dummy photodiode is used to track and compensate for leakage currents, allowing the circuit to maintain high conversion gain by canceling out harmful leakage effects
2Power
If conventional CTIA pixel circuits are used, then charge amplification is achieved, but circuit area is large
Solution Approach 1:
The patent merges the multiplexer function with the CTIA input node by directly connecting the photodiode output to the amplifier input without a separate biased multiplexer stage. This integration eliminates redundant components and reduces pixel area while maintaining charge transfer and amplification functions
Solution Approach 2:
The amplifier input node serves multiple functions simultaneously: it acts as the charge collection node from photodiodes, the virtual ground for transimpedance conversion, and the input to the integration capacitor. This multi-functionality reduces the number of separate components needed, thereby reducing overall pixel area
3Ease of operation
If biased multiplexer is used, then charge transfer is controlled, but noise increases and dynamic range is consumed
Solution Approach 1:
The patent changes the multiplexer bias parameter from a non-zero voltage to zero voltage. By setting Vmux = 0, the patent eliminates the voltage-driven noise and dynamic range consumption associated with biased multiplexers while maintaining the ability to control charge transfer through the zero-biased switch configuration
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 approach enables a higher conversion gain while minimizing leakage current and reducing the area required per pixel, enhancing the performance and efficiency of CTIA pixel circuits in image sensors.
Implementation Method 1
charge is collected in a photoelectric conversion device of the pixel circuit as a result of the impingement of light
Data Source
AI summary
An image sensor and pixel circuit therefor includes a plurality of photoelectric conversion devices, a zero-biased multiplexer connected to the plurality of photoelectric conversion devices, an amplifier including a first input terminal connected to the zero-biased multiplexer, and an output terminal, a capacitor disposed between the first input terminal and the output terminal, and a reset switch disposed between the first input terminal and the output terminal in parallel with the capacitor, the reset switch including a body terminal connected to a common reference voltage.