Pumped Large Full Well Pixel Infrared Sensor
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Solution Overview
Problem
As pixel sizes shrink, the amount of charge that individual pixels can hold decreases, limiting the Signal-to-Noise Ratio (SNR) in infrared imaging, and existing solutions either result in smaller pixels or lower full well sizes.
Innovation Solution
An integration network with a pump voltage source providing two discreet voltage levels, coupled with PMOS transistors and cascode transistors, allows for a larger full well capacity by resetting the integration capacitor to a negative voltage, enabling nearly 5.6V of effective voltage swing and increasing SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If pixel size is reduced to increase resolution, then the number of pixels per area increases, but the full well capacity decreases
Solution Approach 1:
The patent applies parameter changes by utilizing negative voltage levels to extend the voltage swing range of the integration capacitor. By allowing the capacitor to operate with voltages ranging from negative to positive values, the effective storage range is doubled compared to traditional single-polarity operation, thereby maintaining full well capacity despite reduced pixel area.
Solution Approach 2:
The patent introduces an additional voltage dimension by implementing a pumped voltage source that can drive the integration capacitor to negative voltages. This extends the traditional single-dimensional voltage swing (0 to Vmax) into a two-dimensional range (-Vmax to +Vmax), effectively doubling the charge storage capacity without increasing physical pixel dimensions.
2Quantity of substance
If full well capacity is increased to improve SNR, then the integration capacitor size increases, but pixel area increases
Solution Approach 1:
The patent changes the voltage parameter range of the integration capacitor from traditional single-polarity (0 to Vmax) to dual-polarity (-Vmax to +Vmax) operation. This parameter extension allows the same physical capacitor to store twice the charge capacity, improving SNR without requiring larger pixel area.
3Quantity of substance
If integration capacitor voltage swing is increased to store more charge, then full well capacity increases, but the voltage range exceeds supply voltage limits
Solution Approach 1:
The patent implements periodic pumping action using a voltage source that alternates between high and low voltage levels. This periodic voltage pumping temporarily extends the voltage swing beyond normal supply limits during charge transfer operations, then resets to standard levels, enabling large voltage excursions without violating continuous supply voltage constraints.
Solution Approach 2:
The pumped voltage source acts as an intermediary mechanism that temporarily provides extended voltage ranges during critical charge transfer operations. This intermediary voltage source enables the integration capacitor to achieve larger voltage swings than the main supply would otherwise permit, then returns to normal operation afterward.
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 achieves a 60% higher signal-to-noise ratio compared to equivalent non-pumped pixels by effectively increasing the full well potential and maintaining performance in smaller pixels.
Implementation Method 1
a pump voltage source that provides at least two discreet voltage levels including a high voltage level and a low voltage level
Implementation Method 2
an integration capacitor coupled between the injection transistor and the pump voltage source
Data Source
AI summary
A pixel includes an integration capacitor coupled between a system voltage and a pump voltage source and having a first side and a second side. The pixel can be operated to have a large full well by: storing charge from a photo-current source in the integration capacitor; reading out the integration capacitor; resetting the integration capacitor by connecting the capacitor to a column line through a select transistor; while resetting, setting the pump voltage source to the system voltage; and after resetting, setting the pump voltage to ground to create a negative voltage between the integration capacitor and column line.