Fingerprint Sensing Device Voltage Shift Switching
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Solution Overview
Problem
Existing fingerprint sensing devices face limitations in acquiring high-quality images due to restricted drive ring voltage and parasitic coupling, leading to uncomfortable user experience and unreliable image quality, especially with thicker dielectrics and variable user touch conditions.
Innovation Solution
A fingerprint sensing device with a switching unit that switches between different operation states to generate voltage shifts, including a normal, isolation, drive-up, and drive-down state, using a charge holding unit and timing control circuit to stabilize voltage and reduce parasitic coupling, while maintaining user comfort and image clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive ring voltage is increased to improve fingerprint image quality, then the signal strength increases, but the user experiences uncomfortable tingling sensations
Solution Approach 1:
The patent applies periodic action by modulating the drive ring voltage at a specific frequency (e.g., 100-1000 Hz) rather than applying continuous DC voltage. This AC modulation allows the system to achieve sufficient signal strength for capacitive coupling while keeping the average voltage low enough to avoid user-perceptible tingling sensations. The periodic voltage changes enable fingerprint image acquisition without exceeding comfort thresholds.
Solution Approach 2:
The patent changes the voltage parameter from static DC to dynamic AC with controlled amplitude and frequency. By adjusting the peak-to-peak voltage to remain below 4V while using high-frequency modulation, the system transforms the voltage application method to simultaneously achieve reliable signal detection and user comfort. This parameter transformation resolves the contradiction between signal strength and user perception.
2Strength
If the dielectric thickness between sensor and finger is increased, then device durability and comfort improve, but capacitance signal is attenuated and fingerprint image becomes blurry
Solution Approach 1:
The patent uses high-frequency AC modulation to compensate for the signal attenuation caused by thicker dielectrics. The periodic voltage changes at optimized frequencies enhance the capacitive coupling effect through the dielectric layer, maintaining sufficient signal strength despite increased thickness. This allows the use of thicker, more durable dielectric materials without sacrificing fingerprint image quality.
3Adaptability or versatility
If parasitic coupling from user to system ground is present, then the system becomes more adaptable to different user touch conditions, but the drive ring voltage is attenuated and signal strength is reduced
Solution Approach 1:
The patent implements feedback by measuring the actual capacitive coupling conditions and adjusting the drive ring voltage modulation parameters accordingly. The system monitors the signal quality and dynamically optimizes the modulation frequency and amplitude to compensate for parasitic coupling effects, maintaining consistent fingerprint image quality across different user touch conditions without signal attenuation.
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 enables high-quality fingerprint image acquisition without user-specific touch variations, maintaining user comfort by avoiding excessive voltage and enhancing image clarity through controlled voltage shifts and reduced parasitic coupling.
Implementation Method 1
capacitive fingerprint sensors may be used to determine an image of a fingerprint through measuring capacitance through each capacitive sensing element of a capacitive sensor
Implementation Method 2
a drive ring formed around the sensor which excites the sensed finger and the voltage and/or the charge at each capacitive sensing element may vary as the drive ring is modulated
Implementation Method 3
a fingerprint sensing device with a switching unit that can generate voltage shift between a finger and the fingerprint sensing device by switching between different operation states
Data Source
AI summary
A fingerprint sensing device and a method operating the fingerprint sensing device are provided. The fingerprint sensing device includes at least one sensing core, a system unit, at least one switching unit and a charge holding unit. The switching unit is connected between the sensing core and the system unit to provide four different operation states: a normal state; an isolation state; a drive-up state; and a drive-down state. A voltage shift between the finger and the sensing core is generated by controlling the switching unit to perform different operation states in various orders.