Single Transistor CMOS Pixel with Avalanche Amplification
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Solution Overview
Problem
There is a demand for minimizing pixel size in CMOS image sensors while maintaining performance, as existing CMOS image sensors have limitations in manufacturing cost, power consumption, and pixel size, particularly in portable devices like smartphones and digital cameras.
Innovation Solution
The method involves a CMOS image sensor with a pixel array comprising single transistors and photodiodes, where photocharge is accumulated and amplified using a high voltage, and digital pixel signals are generated without the need for an analog-to-digital conversion circuit, allowing for smaller pixel sizes and reduced noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional CMOS image sensors with multiple transistors per pixel are used, then manufacturing cost and device complexity are higher, but pixel size cannot be minimized
Solution Approach 1:
The patent merges multiple transistor functions into a single transistor structure. Specifically, a single transistor is configured to perform both the transfer function (moving photocharge from photodiode to floating diffusion) and the reset function (clearing accumulated charge), replacing what traditionally required multiple separate transistors. This consolidation directly reduces pixel size while maintaining necessary functionality
Solution Approach 2:
The single transistor in the patent is designed to serve multiple functions: it acts as both a transfer transistor and a reset transistor. By making the transistor multi-functional, the patent eliminates the need for separate dedicated transistors for each function, thereby reducing the overall device complexity and enabling smaller pixel dimensions
2Measurement precision
If analog-to-digital conversion circuits are included in each pixel, then signal processing capability is improved, but power consumption and pixel size increase
Solution Approach 1:
The patent extracts the analog-to-digital conversion function from the pixel-level circuitry and relocates it to a separate, dedicated conversion circuit. This allows the pixel itself to remain simple and low-power, while still achieving digital output capability through the external conversion stage. The conversion function is separated from the sensing function to avoid power and size penalties at the pixel level
Solution Approach 2:
The patent moves the analog-to-digital conversion operation from the spatial dimension (within each pixel) to a temporal dimension (sequential conversion after readout). By converting analog signals to digital signals after they are read from the pixel array rather than within each pixel, the system achieves digital processing capability without the power and size overhead of per-pixel conversion circuits
3Measurement precision
If high voltage is applied for photocharge amplification, then signal amplification is improved, but power consumption increases
Solution Approach 1:
The patent applies high voltage in a periodic, pulsed manner rather than continuously. The high voltage is applied only during specific phases of the readout cycle when photocharge amplification is needed, and then reduced or removed during other phases. This periodic application provides necessary signal amplification while significantly reducing average power consumption compared to continuous high voltage application
Solution Approach 2:
The patent dynamically changes the voltage parameter applied to the transistor based on operational requirements. During photocharge transfer and amplification phases, high voltage is applied to maximize signal gain. During other phases such as integration and reset, the voltage is reduced to minimize power consumption. This dynamic parameter adjustment allows the system to achieve high amplification when needed while maintaining low power operation during other phases
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 the creation of smaller, low-power CMOS image sensors with improved performance by directly outputting digital pixel signals, reducing the need for analog-to-digital conversion circuits and minimizing noise and power consumption.
Implementation Method 1
a photodiode connected to a bulk terminal of the single transistor, the photodiode configured to accumulate photocharge generated according to the intensity of incident light
Implementation Method 2
inducing photocharge amplification by avalanche effect by applying a high voltage to at least one terminal among the gate, a source and a drain of the single transistor
Data Source
AI summary
The image sensor includes a pixel array including a plurality of unit pixels each including a single transistor and a photodiode connected to a body of the single transistor, a row driver block configured to enable one of a plurality of rows in the pixel array to enter a readout mode, and a readout block configured to sense and amplify a pixel signal output from each of a plurality of unit pixels included in the row that has entered the readout mode.