Analog Counter Element for Image Sensor Unit Cell
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Solution Overview
Problem
Traditional digital unit cells in image sensors require large and power-consuming digital counter elements to count reset events, leading to increased size and cross-talk, which limits the efficiency of charge accumulation and image processing.
Innovation Solution
A digital unit cell incorporating an analog counter element that is physically smaller, operates with less power, and injects less cross-talk, capable of maintaining a maximum counter value equivalent to traditional digital counters, utilizing a handful of transistors and a charge subtraction circuit to increment a counter value each time the integration capacitor is reset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional digital counter elements are used to count reset events, then the counter value capability is maintained, but the size and power consumption increase
Solution Approach 1:
The patent replaces the traditional digital counter circuit with an analog counter element that uses a capacitor to store charge representing the count value. This substitution of digital electronics with an analog electrical storage mechanism reduces power consumption while maintaining the counting function, as the capacitor holds the count state without requiring continuous power for clock operations or logic circuitry.
Solution Approach 2:
The patent changes the fundamental parameter representation from digital voltage levels to analog charge quantity on a capacitor. The counter value is encoded as the amount of charge stored, allowing the system to maintain counting capability with significantly lower power consumption since capacitors can hold charge states without active power consumption during the hold period.
2Quantity of substance
If traditional digital counter elements are used to count reset events, then the counter value capability is maintained, but the device size increases
Solution Approach 1:
The patent replaces the traditional digital counter circuit with an analog counter element that uses a capacitor to store charge representing the count value. This substitution of digital electronics with an analog electrical storage mechanism reduces the physical area required, as a single capacitor occupies less space than the multiple logic gates, flip-flops, and interconnects required for a digital counter of equivalent capability.
Solution Approach 2:
The patent changes the fundamental parameter representation from digital voltage levels to analog charge quantity on a capacitor. The counter value is encoded as the amount of charge stored, allowing the system to maintain counting capability with significantly reduced device area since capacitors can hold charge states without requiring the complex digital circuitry of traditional counters.
3Productivity
If traditional digital counter elements are used to count reset events, then the counting function is achieved, but cross-talk increases
Solution Approach 1:
The patent replaces the traditional digital counter circuit with an analog counter element that uses a capacitor to store charge representing the count value. This substitution eliminates the high-speed switching edges and logic transitions in digital counters that generate electromagnetic interference and cross-talk, as capacitors charge and discharge more smoothly and can be isolated more effectively in the analog domain.
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
The analog counter element allows for efficient charge accumulation and image processing with reduced power consumption and size, while maintaining equivalent counter value capabilities to traditional digital counters, enhancing the overall performance of image sensors.
Implementation Method 1
an array of unit cells (i.e., a focal plane array) that receives light via a lens. The received light causes each unit cell in the array to accumulate an electric charge proportional to the light intensity at its location
Implementation Method 2
the charge is accumulated on a capacitive element which effectively integrates charge, producing a voltage that corresponds to the intensity of the flux over a given time interval called an integration interval or integration period
Data Source
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AI summary
According to one aspect, embodiments herein provide a digital unit cell comprising a photodiode, an integration capacitor, a comparator configured to compare a voltage across the integration capacitor with a threshold voltage and to generate a control signal at a first level each time the voltage across the integration capacitor is greater than the threshold voltage, a charge subtraction circuit configured to receive the control signal at the first level and to discharge accumulated charge on the integration capacitor each time the control signal at the first level is received, at least one analog counter configured to receive the control signal at the first level from the comparator and to decrease a count voltage by a fixed amount each time the control signal at the first level is received from the comparator, and a counter readout circuit configured to provide the count voltage to an image processing circuit.