THz Image Sensor Pixel Unit With Difference Circuit
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Solution Overview
Problem
Conventional THz electromagnetic radiation imaging devices face challenges in obtaining real-time images due to the need for lengthy data collection, image distortion with moving objects, and complexity in achieving high signal-to-noise ratios, particularly when dealing with objects that require fast inspection and low signal levels.
Innovation Solution
A small-sized image sensor with a pair of photodiodes and a difference circuit that outputs the difference between signals from each photodiode, allowing for simultaneous detection of modulation without phase bias control, and improved signal-to-noise ratio through the use of polarized and wavelength filters with different transmission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single receiver is used to collect THz electromagnetic radiation data, then the device structure is simple, but the image acquisition time becomes excessively long and real-time imaging is impossible
Solution Approach 1:
The single receiver is divided into multiple pixel units arranged in a two-dimensional array. Each pixel unit independently detects THz radiation, enabling parallel data collection across the entire field of view. This segmentation transforms a sequential detection process into a parallel one, achieving real-time imaging capability.
Solution Approach 2:
The detection system transitions from one-dimensional sequential scanning to two-dimensional simultaneous detection by arranging pixel units in a matrix configuration. This dimensional change allows all spatial information to be captured in a single measurement cycle, eliminating the time required for scanning.
2Device complexity
If conventional imaging methods are used with moving objects, then the imaging process is simple, but image distortion occurs due to the long data collection time
Solution Approach 1:
The two-dimensional pixel array continuously captures THz radiation from the entire field of view simultaneously, maintaining uninterrupted detection of moving objects. This continuous simultaneous detection eliminates the gaps and delays inherent in sequential scanning methods, preserving image accuracy for dynamic subjects.
3Measurement precision
If phase bias control is implemented to improve signal-to-noise ratio, then the detection sensitivity increases, but the device complexity and control difficulty increase
Solution Approach 1:
Each pixel unit independently processes its detected signal through on-chip difference circuits that automatically calculate signal differences without requiring external phase bias control. The system achieves high signal-to-noise ratio through self-contained differential detection at each pixel, eliminating the need for complex centralized phase control mechanisms.
4Adaptability or versatility
If multiple photodiodes per pixel are used to detect different polarization components, then the detection capability improves, but the pixel unit area and device complexity increase
Solution Approach 1:
Multiple photodiodes for detecting different polarization components are integrated within each pixel unit, merging the detection functions into a compact structure. The difference circuit within each pixel processes signals from these photodiodes to extract polarization information, achieving versatile detection capability without proportionally increasing overall device complexity.
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
Enables fast and accurate image acquisition without relying on object conditions, reducing image distortion and complexity, and enhancing signal quality even at low signal levels by integrating and outputting difference signals in real-time.
Implementation Method 1
each of the plurality of pixel units includes: a first photodiode and a second photodiode
Implementation Method 2
a first polarized light filter above the first photodiode; and a second polarized light filter above the second photodiode, wherein the first polarized light filter and the second polarized light filter each have different polarized light transmission characteristics
Data Source
AI summary
To provide a small-size image sensor and electromagnetic radiation imaging device which can obtain a good image without relying on the condition of an object, the image sensor including a plurality of pixel units arranged two-dimensionally, wherein each of the plurality of pixel units includes: a first photodiode and a second photodiode; a readout circuit which reads a signal generated by the first photodiode and a signal generated by the second photodiode, and outputs the read signals, the readout circuit being connected to the first photodiode and the second photodiode; and a difference circuit which outputs a difference signal corresponding to a difference between the signal read from the first photodiode and the signal read from the second photodiode, the difference circuit being connected to the readout circuit.