Optical Trigger Distribution for Large Format Imager Timing Skew
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Solution Overview
Problem
Conventional imager technologies face challenges in achieving shutter times below a few nanoseconds for high-speed, large-format detectors, particularly in distributing exposure control signals effectively across millions of pixels, leading to issues with timing skew and jitter, which limits their dynamic range and contrast in applications like plasma diagnostics and high-speed radiographic imaging.
Innovation Solution
The development of a large-format imager with a pixel architecture that includes photodiodes, reset circuits, select circuits, photoswitches, inverters, and control circuitry for generating integration control signals, combined with optical and electrical signal distribution trees to achieve simultaneous sampling and control of integration periods across pixels, utilizing CMOS silicon on insulator technology to isolate photoswitches from radiation and reduce skew and jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional electrical signal distribution is used across large-format detectors, then device complexity is reduced, but timing skew increases to hundreds of picoseconds
Solution Approach 1:
The patent replaces conventional electrical signal distribution with optical signal distribution using a laser source and optical waveguides. The optical trigger signal is distributed to all pixels simultaneously, eliminating the timing skew inherent in electrical distribution across large-format detectors. This substitution of optical for electrical systems resolves the contradiction between system simplicity and timing precision.
2Speed
If shutter times are reduced below a few nanoseconds, then high-speed sampling performance is improved, but conventional pixel architecture cannot achieve this
Solution Approach 1:
The patent uses optical triggering instead of conventional electrical timing signals to control the integration period. The optical pulse directly triggers the photodiodes, enabling shutter times below a few nanoseconds while maintaining reliable integration control through the inherent precision of optical timing.
Solution Approach 2:
The patent changes the fundamental parameter of signal transmission from electrical to optical domain. This parameter change enables achieving shutter times below a few nanoseconds, as optical signals can be distributed simultaneously across the entire detector array without the propagation delays that limit electrical systems.
3Manufacturing precision
If optical trigger distribution is used, then timing skew is reduced, but photoswitches must be isolated from radiation
Solution Approach 1:
The patent introduces an intermediary optical layer (optical waveguides and photoswitches) that mediates between the electrical control system and the photodiode array. The photoswitches are isolated from radiation by being positioned in the optical path rather than directly exposed to the measured radiation, allowing them to convert optical trigger signals to electrical signals without being affected by the radiation field.
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 shutter times below a few nanoseconds, providing high-speed sampling performance for applications like x-ray imaging, with reduced timing skew and jitter, and allows for flexible spatial sampling, improving the dynamic range and contrast of high-speed imaging systems.
Implementation Method 1
Each pixel includes a photodiode to convert electromagnetic radiation into an electrical charge
Implementation Method 2
a photoswitch to convert an optical trigger pulse, received from the trigger means, into an electrical signal
Data Source
AI summary
A large format imager includes an array of pixels for converting electromagnetic radiation into electrical signals and a trigger to from an optical pulse so as to trigger the pixels to generate an integration period. Each pixel includes a photodiode to convert light intensity of high-frequency radiation into an electrical charge, a reset switch to reset the photodiode, circuitry to enable sampling of the electrical charge produced by the photodiode, a photoswitch to convert an optical trigger pulse, received from the trigger, into an electrical signal, an inverter to produce a control signal corresponding to the electrical signal produced by the photoswitch, and control circuitry to locally generate integration control signals. The integration control signals control a start of an integration period for the photodiode, duration of the integration period for the photodiode, and the sampling of the electrical charge produced by the photodiode. The large format imager may also include a trigger for producing an electrical pulse so as to trigger the pixels to generate an integration period and tree type electrical distribution system for propagating the electrical pulse to all the pixels, wherein each pixel includes a global repeater circuit to propagate a first edge of said electrical pulse along said tree type electrical distribution system and a local repeater circuit to provide a local array of pixels with the first edge of the electrical pulse.