Solid-state imaging device offset voltage correction
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Solution Overview
Problem
Solid-state imaging devices using compound semiconductor photodiodes face challenges with temperature sensitivity and large amplifier layouts, limiting pixel density and requiring expensive temperature control or large amplifiers with significant offset voltages.
Innovation Solution
A solid-state imaging device with a pixel unit configuration that includes a main amplifier, capacitive elements, switches, and a correction unit, allowing for charge accumulation and voltage output without needing strict temperature control, and enabling a compact layout by reducing effective offset voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strict temperature control is performed using expensive coolers, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the temperature control requirement from the system by introducing a correction unit that separately measures and compensates for temperature-induced offset voltage changes. This allows the main amplifier to operate without strict temperature control while maintaining measurement precision through software correction.
Solution Approach 2:
The correction unit acts as an intermediary that measures the offset voltage at different temperatures and creates a correction table. This intermediary component enables the system to compensate for temperature effects without requiring the main amplifier to be temperature-stable, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If an amplifier with very small offset voltage is used, then measurement precision is improved, but layout area increases
Solution Approach 1:
The patent extracts the offset voltage correction function from the main amplifier design and places it in a separate correction unit. This allows the use of standard amplifiers with larger layout areas while maintaining measurement precision through digital correction of the offset voltage.
Solution Approach 2:
The correction unit creates a digital copy or model of the offset voltage behavior at different temperatures through measurement and storage in a correction table. This digital representation allows precise compensation without requiring the physical amplifier to have special low-offset characteristics, thus reducing layout area requirements.
3Productivity
If the number of photodiodes is increased, then productivity is improved, but pitch between pixels increases
Solution Approach 1:
The patent extracts the temperature compensation function from each pixel unit and consolidates it in a shared correction unit. This reduces the area required per pixel, allowing more photodiodes to be packed into the same area without increasing pitch, thus improving productivity while maintaining compact dimensions.
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 configuration simplifies or eliminates the need for temperature control and allows for a narrower pixel pitch, enhancing the imaging device's efficiency and scalability.
Implementation Method 1
a feedback capacitive element provided between the first input terminal and the output terminal of the main amplifier, and for accumulating a charge generated in the photodiode in response to light incidence
Implementation Method 2
each of the plurality of pixel units includes a photodiode connected to the first input terminal of the main amplifier
Data Source
AI summary
A solid-state imaging device includes M pixel units to and a correction unit. The pixel unit includes a main amplifier, a capacitive element, a first switch, a second switch, a photodiode, a feedback capacitive element, and an initialization switch. The correction unit includes a null amplifier, a capacitive element, a first switch, and a second switch. An effective offset voltage of the main amplifier is small.