Fingerprint Sensor Sensing Element Parasitic Capacitance Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fingerprint sensors face challenges in sensitivity due to parasitic capacitances, which affect the ability to distinguish between fingerprint ridges and valleys, leading to reduced touch sensitivity and accuracy.
Innovation Solution
The fingerprint sensor design includes a substrate, sensing electrode, shielding plate, and conductive plates configured to detect capacitance, with an amplifier and feedback capacitor, where the sensitivity is directly proportional to the input voltage and inversely proportional to the feedback capacitance, allowing for enhanced sensitivity independent of parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If parasitic capacitances are present between the sensing electrode and substrate/shielding plate, then the sensor structure is simple, but the sensitivity is reduced
Solution Approach 1:
The patent introduces a feedback capacitor connected between the inverting terminal and output of the amplifier, creating a feedback mechanism that compensates for parasitic capacitances. The feedback capacitor value is specifically designed to counteract the effect of parasitic capacitances between the sensing electrode and substrate/shielding plate, thereby maintaining sensor sensitivity while managing circuit complexity through controlled feedback.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by introducing controlled capacitance values. The feedback capacitor is designed with a specific capacitance value that, when combined with the input voltage, creates a signal that compensates for parasitic effects. This parameter change approach allows the system to maintain sensitivity despite the presence of parasitic capacitances.
2Reliability
If the feedback capacitor capacitance is increased, then the sensitivity is improved, but the stability is reduced
Solution Approach 1:
The patent optimizes the feedback capacitor value to achieve a balance between sensitivity and stability. By carefully selecting the capacitance value, the system achieves sufficient sensitivity improvement while maintaining circuit stability. The feedback capacitor value is designed to provide the necessary compensation without causing excessive amplification that would lead to instability.
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 enhances the sensitivity of the fingerprint sensor, making it more effective in distinguishing touch events and improving data security by reducing the impact of parasitic capacitances, resulting in a more reliable user authentication system.
Implementation Method 1
The sensing electrode is configured to detect a capacitance in response to a touch event on the fingerprint sensor
Implementation Method 2
The amplifier includes an inverting terminal coupled to a second plate of the first pair of conductive plates, and a non-inverting terminal to receive a voltage that is a fraction of the input voltage. The sensitivity of the fingerprint sensor is directly proportional to the input voltage.
Data Source
AI summary
A fingerprint sensor is disclosed. The fingerprint sensor includes a substrate, a sensing electrode, a shielding plate, a first pair of conductive plates and an amplifier. The sensing electrode is configured to detect a capacitance in response to a touch event on the fingerprint sensor, and configured to selectively receive or not receive an input voltage. The shielding plate is configured to selectively receive the input voltage or is coupled to a reference voltage level. The first pair of conductive plates includes a first plate selectively coupled to the sensing electrode. The amplifier includes an inverting terminal coupled to a second plate of the first pair of conductive plates, and a non-inverting terminal to receive a voltage that is a fraction of the input voltage. The sensitivity of the fingerprint sensor is directly proportional to the input voltage.