Fingerprint Sensing Circuit for Parasitic Capacitance Compensation
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Solution Overview
Problem
Semiconductor capacitive fingerprint sensors face issues with dynamic range reduction due to parasitic capacitance and offset voltage errors, leading to saturation and reduced accuracy in fingerprint detection.
Innovation Solution
A fingerprint detection device employing multiple integrators with a processor-controlled integration process, where the integration order is altered between a first and second integrator, and a compensator adjusts output values to minimize differences between integration processes, thereby reducing parasitic capacitance and offset voltage errors, and increasing the dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one integrator is used to amplify the electrical signal, then the amplification function is simple, but the base capacitance and parasitic capacitance form a large base signal that saturates the integrator and reduces dynamic range
Solution Approach 1:
The single integrator is divided into multiple integrators (first integrator, second integrator, etc.). Each integrator processes the signal separately, allowing the base capacitance and parasitic capacitance to be distributed across multiple integration cycles rather than forming a large base signal in one integrator, thereby preventing saturation and increasing dynamic range.
Solution Approach 2:
The multiple integrators operate in periodic cycles, with each integrator performing integration for a specific time period and then being reset. This periodic operation allows the base signal to be accumulated and reset in stages, preventing any single integrator from being saturated by the full base signal while maintaining the amplification function.
2Reliability
If multiple integrators are used to increase dynamic range, then the output dynamic range is improved, but the processing complexity and number of components increase
Solution Approach 1:
Multiple integrators are merged into a single amplifier unit that processes signals from multiple nodes. The integrators share common control logic and operate in a coordinated manner under processor control, reducing the overall system complexity compared to having separate amplification circuits for each integrator.
Solution Approach 2:
The multiple integrators are designed to perform multiple functions: they amplify the electrical signal, reduce parasitic capacitance effects, and enable periodic signal processing. Each integrator can be reused across different time periods and nodes, making the system more efficient and reducing the need for additional dedicated components.
3Measurement precision
If integration is performed repeatedly to reduce parasitic capacitance errors, then the measurement precision is improved, but the processing time increases
Solution Approach 1:
The multiple integrators operate in continuous periodic cycles, with each integrator performing integration during its assigned time period and then being reset. This continuous operation allows the system to maintain high measurement precision through repeated integration while minimizing idle time and ensuring that the fingerprint detection process proceeds efficiently without unnecessary delays.
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 fingerprint sensor outputs, improves accuracy by reducing parasitic capacitance and offset voltage errors, and increases the number of integrations, leading to more precise fingerprint detection.
Implementation Method 1
a first integrator configured to amplify an electrical signal received from the touch panel to a first signal of a first polarity and a second integrator configured to amplify the electrical signal to a second signal of a second polarity
Data Source
AI summary
Disclosed are a fingerprint detection device and a method therefor. A fingerprint detection device includes: a touch panel; at least one amplifier including a first integrator amplifying an electrical signal received from the touch panel to a signal of a first polarity and a second integrator amplifying the electrical signal to a signal of a second polarity; and a processor configured to control the amplifier to perform a first integration process and a second integration process with respect to a plurality of electrical signals received from a plurality of nodes of the touch panel.