Capacitive Fingerprint Sensor Base Cancellation for Wider Dynamic Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Semiconductor capacitive fingerprint sensors face issues with dynamic range reduction due to parasitic and base signals, leading to saturation and decreased signal-to-noise ratio, which limits the accuracy and efficiency of fingerprint acquisition.
Innovation Solution
Incorporating an integrator, trigger, and base cancelling circuit to generate and adjust output signals within predetermined thresholds, preventing saturation and increasing the dynamic range by canceling parasitic and base signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an integrator is used to store charges from the fingerprint capacitor, then the output signal is generated and transferred to the trigger, but the base signal from parasitic and base capacitors causes the integrator to saturate, reducing the dynamic range
Solution Approach 1:
The patent extracts and separates the base signal cancellation function from the main integrator circuit by introducing a dedicated base cancelling circuit. This circuit specifically targets and removes the base signal component generated by parasitic and base capacitors, allowing the integrator to focus on processing the valid fingerprint signal without saturation from the large base signal.
Solution Approach 2:
The trigger circuit serves as an intermediary between the integrator and the base cancelling circuit. It monitors the output signal from the integrator and activates the base cancelling circuit only when the signal exceeds a predetermined threshold, thereby coordinating the operation of these circuits to optimize performance while preventing saturation.
2Power
If the base signal is amplified by the amplifier, then the output signal is enhanced, but the amplified base signal far exceeds the valid signal, causing the integrator to saturate and reducing the output dynamic range
Solution Approach 1:
The base cancelling circuit performs preliminary cancellation of the base signal before it can cause saturation in the integrator. By generating a base cancelling signal that opposes and neutralizes the base signal component, the system prevents the harmful effect of base signal amplification while preserving the useful fingerprint signal amplification.
Solution Approach 2:
The system dynamically adjusts the cancellation amount based on the output signal level from the integrator. When the output signal exceeds the predetermined threshold, the base cancelling circuit is activated with appropriate gain settings to cancel the base signal; otherwise, it remains inactive, thereby adaptively managing the dynamic range.
3Adaptability or versatility
If the base cancelling circuit is triggered when the output signal exceeds a predetermined threshold, then the base cancelling signal is generated to adjust the output signal within the threshold, but additional circuits increase the device complexity
Solution Approach 1:
The trigger circuit performs multiple functions: it monitors the integrator output signal level, compares it against a predetermined threshold, and activates the base cancelling circuit only when necessary. This multi-functional design avoids the need for separate monitoring and control circuits, thereby limiting the increase in device complexity while achieving dynamic range extension.
4Measurement precision
If the valid signal is relatively smaller compared to the amplified base signal, then the signal-to-noise ratio decreases, but increasing amplification further worsens the saturation problem
Solution Approach 1:
The patent converts the harmful base signal into a beneficial cancellation reference. By using the base signal itself (or a version of it) to generate the base cancelling signal, the system transforms the source of the problem into the solution, thereby improving the signal-to-noise ratio for the valid fingerprint signal without causing saturation.
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 solution effectively expands the dynamic range of the fingerprint sensor, enhancing signal-to-noise ratio and reducing power consumption, while maintaining accurate fingerprint detection.
Implementation Method 1
an integrator, configured to store charges from a fingerprint capacitor to generate an output signal
Data Source
AI summary
Embodiments of the present disclosure hereinafter provide a capacitive fingerprint sensor. The capacitive fingerprint sensor includes: an integrator, a trigger and a base cancelling circuit; where the integrator is configured to store charges from a fingerprint capacitor to generate an output signal and transfer the output signal to the trigger, the trigger is configured to trigger the base cancelling circuit to generate a base cancelling signal and output the base cancelling signal to the integrator if the output signal exceeds a predetermined threshold, and the base cancelling signal is used to adjust the output signal of the integrator to fall within the predetermined threshold. In this way, the integrator is prevented from simply coming to saturation, and thus a dynamic range of the integrator is increased.