Capacitive Fingerprint Sensing Circuit for Base Signal Cancellation
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Solution Overview
Problem
Current capacitive fingerprint sensors face challenges in effectively canceling base signals, leading to reduced fingerprint identification precision and higher power consumption due to the need for high-precision signal sources.
Innovation Solution
A fingerprint detection circuit with a summing unit that combines output signals from multiple detection units to cancel base signals, utilizing a simple structure that reduces chip area and power consumption, enhancing fingerprint identification precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-precision signal source is used to cancel base signals, then fingerprint identification precision is improved, but power consumption increases and device complexity increases
Solution Approach 1:
The patent creates a virtual reference signal by copying and processing the actual fingerprint signal itself. Instead of using a separate high-precision signal source to generate a canceling signal, the system processes the detected signal VPXL through a model that simulates the base signal characteristics, then subtracts this modeled base signal from the original signal. This copying approach eliminates the need for complex external signal sources while maintaining cancellation effectiveness.
Solution Approach 2:
The patent introduces a signal processing model as an intermediary between the detected signal and the base signal cancellation process. This model (comprising components like multipliers, adders, and filters) acts as a mediator that generates the virtual reference signal needed for cancellation. By using this intermediary processing stage instead of a direct high-precision signal source, the system achieves base signal cancellation with lower power consumption and reduced device complexity.
2Measurement precision
If a high-precision signal source is used to cancel base signals, then fingerprint identification precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex external signal sources with an internal signal processing model that copies and processes the detected signal to generate a virtual reference. This copying mechanism uses standard CMOS circuit components (multipliers, adders, filters) that are already present in the fingerprint sensor, thereby reducing device complexity and cost while achieving the same base signal cancellation effect.
Solution Approach 2:
The patent makes the existing signal processing components serve multiple functions. The same amplifiers, filters, and processors used for normal fingerprint signal processing are also utilized to generate the virtual reference signal for base signal cancellation. This multi-functionality eliminates the need for separate high-precision signal source hardware, thereby reducing device complexity and cost.
3Adaptability or versatility
If the coupling capacitance dynamically changes, then the signal amplitude follows the capacitance variation, but base signal cancellation becomes ineffective
Solution Approach 1:
The patent implements a feedback mechanism where the detected signal VPXL is fed back into the signal processing model to continuously update the virtual reference signal. The model uses the actual detected signal (which already reflects coupling capacitance variations) to generate an updated base signal estimate, which is then subtracted from the original signal. This feedback loop ensures that the base signal cancellation remains effective even when coupling capacitance dynamically changes, as the virtual reference signal continuously adapts to match the actual signal conditions.
Solution Approach 2:
The patent employs dynamic signal processing where the virtual reference signal is not fixed but continuously updated based on the detected signal characteristics. The signal processing model dynamically adjusts the generated base signal estimate to match current coupling capacitance conditions, enabling effective cancellation despite dynamic changes in the electrical environment.
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 effectively cancels base signals, improving fingerprint identification precision and reducing power consumption compared to traditional high-precision signal source-based systems.
Implementation Method 1
the capacitance (or inductance) is different because a practical distance from the fingerprint of the finger to the detection unit is different due to different depths of the grain of the finger
Data Source
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AI summary
The present invention discloses a fingerprint detection circuit, including a plurality of detection units arranged in an array, and further including a summing unit; wherein the detection units include a first detection unit and a second detection unit, the first detection unit and the second detection unit being respectively connected to the summing unit, the summing unit conducting a summing operation for an output signal of each second detection unit and an output signal of the first detection unit to cancel a base signal in the output signal of each second detection unit to acquire a useful signal including fingerprint information.