Gain Matching for Electron Multiplication Imager Pixels
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Solution Overview
Problem
In two-dimensional arrays of imaging pixels employing electron multiplication, variations in design and process tolerances lead to differing electron multiplication gains between pixels, causing inconsistencies in signal charge and output voltage, especially after multiple passes through EM gain regions.
Innovation Solution
A method to equalize gain across EM pixels by adjusting the voltage difference between DC gates and EM clocked gates, ensuring all pixels achieve a uniform gain by selectively trimming DC gate voltages during the clocking process, with common phase 1 and EM clock gates applied across rows and columns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electron multiplication is employed in imaging pixels to amplify signal charge, then sensitivity and signal strength are improved, but variations in gain between pixels occur due to design and process tolerances
Solution Approach 1:
The patent adjusts the voltage applied to DC gates as a controllable parameter to compensate for variations in electron multiplication gain between pixels. By changing the voltage parameter, the gain of each pixel can be tuned to achieve uniformity across the array, resolving the contradiction between achieving high gain and maintaining gain uniformity.
2Power
If multiple passes through EM gain regions are used to increase charge, then signal amplification is improved, but variations in pixel intensity values increase due to cumulative gain differences
Solution Approach 1:
The patent applies preliminary voltage adjustments to DC gates before the multiple passes through EM gain regions. By pre-compensating for gain variations, the cumulative effect of multiple passes produces uniform pixel intensity values across the array, rather than amplifying the variations.
3Manufacturing precision
If individual pixel gain adjustment is implemented, then gain uniformity is improved, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent merges the gain adjustment function into the existing clocking structure by using DC gates that are already part of the pixel architecture. The voltage adjustments are applied through existing gate structures rather than adding separate control circuits, thus achieving gain matching without significantly increasing device complexity.
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 ensures that all pixels in the array produce consistent pixel intensity values, achieving a desired image quality by maintaining the voltage difference between DC and EM clocked gates, thereby reducing variations and enhancing image uniformity.
Implementation Method 1
a form of gain via impact ionization can be achieved in a CCD device... The original gate 4 wherein the charge was first accumulated is then biased into impact ionization
Data Source
AI summary
A method and apparatus for equalizing gain in an array of electron multiplication (EM) pixels is disclosed, each pixel having one or more impact ionization gain stages with implants to achieve charge transfer directionality and comprising a phase 1 clocked gate, an EM clocked gate, and two DC gates formed between the phase 1 clocked gate and the EM clocked gate, comprising the steps of (a) applying initial voltages to each of the DC gates and the EM clocked gates of at least two pixels of a plurality of pixels; (b) clocking phase 1 clock gates and an EM clock gates associated with the at least two pixels of the plurality of pixels a predetermined number of times to achieve an average pixel intensity value after impact ionization gain; and (c) selectively adjusting the difference in voltage between the DC gate and corresponding EM clocked gate of the at least two pixels of the plurality of pixels until the difference between the resulting pixel intensity values and the average pixel intensity value needed to produce a desired uniform gain image is below a predetermined threshold.