Pipelined Amplifier Time Delay Integration Circuit
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Solution Overview
Problem
Conventional time delay and integration (TDI) circuits, such as those using charge coupled devices (CCDs) or bucket-brigade device (BBD) circuits, are costly and radiation intolerant, and suffer from inefficiencies when the number of detector channels increases, particularly in applications requiring low light and high resolution like remote satellite imaging.
Innovation Solution
A pipelined time delay integration circuit with a first and second stage, where the second stage includes a reset switch that couples the first and second integrators, allowing integrated voltage from the first stage to propagate to the second stage between time intervals, implemented using MOS processing techniques on a silicon chip with a detector array of radiation detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional TDI circuits use CCDs or BBD circuits, then signal integration capability is achieved, but manufacturing cost increases and radiation tolerance decreases
Solution Approach 1:
The patent uses standard MOS circuit copying techniques to replicate the TDI functionality across multiple detector channels. Each channel uses identical MOS-based integrator circuits that can be mass-produced using conventional semiconductor fabrication processes, eliminating the need for expensive specialized CCD or BBD manufacturing while maintaining signal integration capability.
Solution Approach 2:
The patent changes the fundamental operating parameters from charge-mode (CCD) or voltage-mode (BBD) to current-mode MOS operation. This parameter change enables compatibility with standard MOS fabrication processes, significantly reducing manufacturing cost while achieving the same TDI function through different physical mechanisms.
2Reliability
If conventional TDI circuits use CCDs or BBD circuits, then signal integration capability is achieved, but radiation tolerance decreases
Solution Approach 1:
The patent employs standard MOS circuit designs that are inherently more radiation tolerant than CCD or BBD circuits. By copying proven radiation-hardened MOS circuit architectures across all TDI channels, the system achieves both signal integration capability and improved radiation tolerance suitable for satellite and space applications.
Solution Approach 2:
The patent substitutes the mechanical charge transfer mechanism of CCDs with electronic current-mode signal processing using MOS transistors. This substitution eliminates the charge transfer inefficiencies and radiation sensitivity inherent in CCD mechanical operations, providing a more robust solution for radiation environments.
3Measurement precision
If the number of detector channels in TDI increases, then signal-to-noise ratio improves, but transfer inefficiencies increase in conventional circuits
Solution Approach 1:
The patent replaces the mechanical charge transfer mechanism with electronic current-mode signal summation. In this approach, multiple detector channel signals are summed as currents at each integrator node, eliminating the charge transfer losses that accumulate in conventional CCD or BBD systems as the number of channels increases. This enables efficient handling of large detector arrays with high signal-to-noise ratios.
Solution Approach 2:
The patent introduces current-mode integrators as intermediary elements between detector channels and the final output. These integrators sum multiple channel signals through current addition, providing a scalable architecture where transfer efficiency is maintained regardless of the number of detector channels, thereby preserving productivity while improving measurement precision.
4Object-affected harmful factors
If CCD processing is used for radiation tolerant hardware, then specialized radiation hardening is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the fundamental operating mode from charge-based (CCD) to current-based (MOS) operation. This parameter change enables the use of standard MOS fabrication processes that are simpler and more cost-effective than specialized CCD processing, while still achieving radiation tolerance through the inherent robustness of current-mode MOS circuits in radiation environments.
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 solution provides a robust and cost-effective method for integrating signals from a line of sensors, achieving improved signal-to-noise ratio without the expense and radiation limitations of CCDs, and efficiently handling large numbers of detector channels.
Implementation Method 1
The first integrator integrates an output signal from a first detecting element during a first time interval
Implementation Method 2
The reset switch has an input that is coupled to an output of the first integrator. The second integrator has a first input for receiving a signal from a separate detecting element and a second input coupled to an output of the reset switch
Data Source
AI summary
A series of time delay integration TDI stages each integrate a photocurrent from a separate detector such as detectors in an array. In a first stage 20, a first integrator is initialized with a fixed bias 30, and integrates a signal from a first detector 22 during a first time interval. Next, a reset switch 26n causes that integrated first detector signal to bias a second integrator 24n. During a second integration interval, the second integrator integrates a signal from a second detector 22n. Multiple stages may be arranged in series so that an integrated signal from a previous stage biases an integrator in the current stage. At a final stage, an Nth integrator outputs the resulting signal Vfinal. Any bias used to initialize the first integrator is removed from Vfinal to achieve a total integrated signal from the detectors. A bi-directional switch 38 at each stage enables a forward or backward scan of the detectors.