Dual-Mode Sensor Pixel for Optical and Capacitive Recognition
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Solution Overview
Problem
Conventional image sensors are limited to a single operational mode (optical, capacitive, resistive, thermal, or ultrasonic), which restricts their ability to leverage the advantages of other modes for fingerprint and document recognition.
Innovation Solution
A sensor pixel design that selectively operates in either optical or capacitive mode based on a mode selection voltage, utilizing transistors and photoconductors to switch between modes, with a coupling capacitor and sensing electrode to form a capacitor with the recognition target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional image sensor uses one specific operational mode (optical, capacitive, resistive, thermal, or ultrasonic), then it can be designed and manufactured with simplicity and reliability, but it cannot leverage the advantages of other modes for fingerprint and document recognition
Solution Approach 1:
The sensor pixel is designed to perform multiple functions by integrating both optical sensing (via photoconductor) and capacitive sensing (via sensing electrode) capabilities within a single pixel structure. The mode selection transistor enables the pixel to switch between optical mode and capacitive mode, allowing the same hardware to recognize both fingerprints and documents effectively
Solution Approach 2:
The sensor pixel incorporates dynamic switching capability through the mode selection transistor, which can change the operational state of the pixel based on the type of recognition needed. The transistor switches between connecting the photoconductor (optical mode) and the sensing electrode (capacitive mode), enabling adaptive operation without requiring separate dedicated sensors for each mode
2Reliability
If a sensor pixel uses both optical and capacitive modes, then it can recognize both fingerprints and documents effectively, but the transistor switching and mode selection mechanism increases device complexity
Solution Approach 1:
The sensor pixel integrates multiple sensing functions (optical and capacitive) into a single unified structure, allowing one pixel to perform recognition for both fingerprints and documents. This eliminates the need for separate dedicated sensors and reduces overall system complexity despite the dual-mode capability
Solution Approach 2:
The mode selection transistor is pre-configured to switch between optical and capacitive modes based on the recognition task requirements. The transistor's gate is connected to a mode selection signal that determines the operational state before the actual recognition process begins, enabling seamless mode transition without adding complex real-time control mechanisms
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 effective recognition of fingerprints and documents by adapting the sensor pixel's operation to either optical or capacitive mode, enhancing the sensor's versatility and performance.
Implementation Method 1
An off current of the photoconductor may change depending on light to be irradiated to the photoconductor
Implementation Method 2
The sensing electrode may form a capacitor together with a fingerprint which is a recognition target when the first transistor is turned off
Data Source
AI summary
There is provided a sensor pixel, including: a first transistor controlled depending on a mode selection voltage supplied to one end thereof; a second transistor including a gate connected to the other end of the first transistor; and a photoconductor connected to one end of the second transistor, wherein the sensor pixel operates in an optical mode when the first transistor is turned on, and the sensor pixel operates in a capacitive mode when the first transistor is turned off.