Asynchronous Image Sensor ADC With Charge Injection for Wide Dynamic Range
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Solution Overview
Problem
Existing image-sensing microelectronic devices face challenges in achieving both good linearity and high conversion dynamic range in analog/digital conversion, particularly when dealing with significant detector currents, leading to potential comparator blocking and insufficient digitization performance.
Innovation Solution
The implementation of an asynchronous analog/digital conversion device with a comparator and charge injector, where the charge injector is commanded to inject charges based on state changes of the comparator output signal, allowing for automatic and asynchronous triggering, and the use of clock-free or asynchronous command means to manage charge injections, enhancing dynamic range and preventing untimely comparator blocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If synchronous ΔΣ modulator with clocked comparator is used, then conversion linearity is improved, but conversion dynamic range is limited and comparator blocking occurs at high detector currents
Solution Approach 1:
The patent transitions from a synchronous clocked system to an asynchronous dynamic system where the comparator operates without a fixed clock signal. The system adapts its operation based on the instantaneous detector current, allowing the comparator to remain reliable across a wider dynamic range by eliminating fixed timing constraints that cause blocking at high currents.
Solution Approach 2:
The invention changes the operational parameters of the comparator from fixed-clock synchronous operation to asynchronous operation triggered by signal level changes. This parameter change allows the system to maintain linearity while expanding the dynamic range and preventing comparator blocking by adapting the timing of operations to the actual signal conditions.
2Reliability
If asynchronous ΔΣ modulator without charge injector is used, then conversion dynamic range is improved, but conversion linearity deteriorates at significant detector currents
Solution Approach 1:
The patent merges the advantages of both synchronous and asynchronous approaches by combining an asynchronous trigger mechanism with a charge injector. This hybrid approach maintains the wide dynamic range of asynchronous operation while adding the linearity correction capability of charge injection, achieving both high dynamic range and good linearity simultaneously.
Solution Approach 2:
The charge injector acts as an intermediary element that corrects linearity errors introduced by the asynchronous operation. By injecting compensating charges based on the comparator output, the system maintains accurate linear conversion across the extended dynamic range that would otherwise suffer from non-linearity.
3Loss of energy
If analog/digital conversion is integrated to each pixel, then consumption and noise are reduced, but device complexity increases
Solution Approach 1:
The patent implements a universal pixel structure where each pixel contains a complete analog-to-digital conversion chain (photodetector, integration capacitor, asynchronous ΔΣ modulator, and charge injector). This multi-functional integration allows each pixel to operate independently with full conversion capability, reducing overall system power consumption and noise while the standardized design manages the complexity through reuse of identical circuit blocks.
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 improved dynamic range and robustness against sudden variations in detector currents, ensuring effective digitization of analog signals while maintaining linearity and preventing comparator blocking, even at high detection current levels.
Implementation Method 1
Each pixel comprises a detector, provided for example with at least one photodiode or at least one phototransistor, provided in order to convert the energy of incident photons on the pixel into electron-hole pairs
Implementation Method 2
with an integration capacitance, the role of which is to store these charges
Implementation Method 3
The comparator 3 commands a charge injector 6 connected to an output of the comparator 3 and intended to inject packets of charges into the capacitor 1
Data Source
AI summary
An analog/digital converter device associated with a detector of an image sensor, including: a comparator capable of receiving the analog signal and delivering a two-states output signal, able to adopt, depending on the analog signal, a first stable state or a second state, a charge injector capable of changing the analog signal by injection of at least one quantity of charges into the capacitor, and a mechanism for commanding the charge injector, capable of receiving the two-state signals and capable of triggering, depending on the two-state signals, plural injections of charges between at least two successive changes in state of the signal, from the first state to the second state and from the second state to the first state.