Hybrid P-N Transistor Comparator for ADC Dynamic Range
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high dynamic range and sensitivity, particularly at low light conditions, due to limitations in analog-to-digital conversion (ADC) dynamic range and operation margin, which affects imaging characteristics in applications like surveillance cameras and biometric authentication devices.
Innovation Solution
A solid-state imaging device with a comparator unit that includes a first amplifying unit with P-type and N-type transistor differential pairs and a second amplifying unit, where P-type and N-type transistors are connected in series, allowing for expanded dynamic range by selectively switching input signals and averaging offset voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional ADC with single-type transistors is used, then the circuit design is simple, but the dynamic range is limited
Solution Approach 1:
The patent merges P-type and N-type transistor differential pairs into a single amplifying unit, creating a hybrid structure that combines the advantages of both transistor types. This merging expands the input voltage range beyond what single-type transistor circuits can achieve, directly resolving the contradiction between circuit simplicity and dynamic range expansion.
Solution Approach 2:
The patent introduces dynamic switching mechanisms that selectively activate P-type or N-type differential pairs based on input signal conditions. This dynamic adaptation allows the circuit to optimize its performance across different voltage ranges, effectively expanding the overall dynamic range while maintaining manageable circuit complexity through controlled adaptability.
2Measurement precision
If the ADC dynamic range is expanded using conventional methods, then sensitivity improves, but fixed pattern noise increases
Solution Approach 1:
The patent applies different transistor types (P-type and N-type) to different differential pairs within the same amplifying unit, creating local quality variations that are strategically utilized. Each transistor type contributes its unique characteristics to specific parts of the input range, improving sensitivity across the expanded dynamic range while the diversity of transistor types helps randomize and reduce fixed pattern noise.
Solution Approach 2:
The patent creates a composite transistor structure by combining P-type and N-type transistors in the same amplifying unit, analogous to using composite materials. This composite approach leverages the complementary characteristics of different transistor types to achieve superior performance, where the combination reduces fixed pattern noise while expanding dynamic range and improving sensitivity.
3Measurement precision
If analog gain is increased to improve low light characteristics, then sensitivity improves, but operation margin decreases
Solution Approach 1:
The patent employs dynamic switching between P-type and N-type differential pairs based on the input signal level and operating conditions. This dynamic operation allows the circuit to maintain optimal performance across varying light conditions while preserving sufficient operation margin, as the switching mechanism prevents the circuit from operating at extreme gain levels where margin would be compromised.
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 solution enhances the dynamic range of the ADC, improving imaging characteristics and sensitivity, especially at low light conditions, by expanding the input voltage range and reducing fixed pattern noise, thereby supporting high-quality image capture in various applications.
Implementation Method 1
a photodiode that performs photoelectric conversion on light
Data Source
AI summary
A solid-state imaging device that is capable of improving an imaging characteristic by enhancing a dynamic range of an ADC is provided. A solid-state imaging device that includes a pixel array including a plurality of pixels outputting a pixel signal by photoelectric conversion, and an AD conversion processing unit that performs AD conversion with respect to the pixel signal, and in which the AD conversion processing unit includes a comparator having a first amplifying unit that includes a pair of first differential pairs constituted of P-type transistors and a pair of second differential pairs constituted of N-type transistors, and a second amplifying unit that amplifies an output of the first amplifying unit, and in which a P-type transistor and an N-type transistor are connected in series is provided.