Capacitance Sensing Circuit With Direct Digital Fingerprint Readout
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Solution Overview
Problem
Conventional fingerprint identification systems using capacitance sensing circuits face challenges due to high circuit complexity, large area occupation, high production costs, and high power consumption, primarily because they require analog-to-digital converters to process analog voltage signals from finger touches.
Innovation Solution
A capacitance sensing circuit that directly converts touch capacitance into digital signals using an integrating circuit, comparator, positive and negative digital-to-analog converting units, control circuit, and logic circuit, eliminating the need for analog-to-digital converters, thereby simplifying the circuit, reducing area, lowering costs, and minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal from the capacitance sensing circuit, then the fingerprint identification accuracy is improved, but the circuit complexity increases, circuit area occupies more space, production cost rises, and power consumption increases
Solution Approach 1:
The patent extracts and eliminates the ADC component from the fingerprint sensing system. Instead of using a separate ADC to convert analog voltage signals to digital signals, the invention integrates the conversion function directly into the capacitance sensing circuit through dual DA converting units that generate complementary digital signals directly from the analog capacitance measurement, thereby removing the need for an external ADC and reducing circuit complexity
Solution Approach 2:
The patent merges the analog-to-digital conversion function with the capacitance sensing function. The dual DA converting units (positive and negative) are integrated into the sensing circuit architecture, combining the signal generation and conversion processes into a unified system that directly outputs digital signals without requiring separate conversion stages
2Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal, then the fingerprint identification accuracy is improved, but the circuit area occupied increases
Solution Approach 1:
The patent removes the ADC component from the system architecture, eliminating the physical space it would occupy on the integrated circuit. The dual DA converting units generate digital signals directly within the compact sensing circuit area, avoiding the need for additional conversion circuitry and reducing overall chip area
Solution Approach 2:
The invention combines the signal conversion function with the sensing elements themselves, integrating what would traditionally be separate functional blocks into a compact unified structure. This merging eliminates the need for separate ADC circuitry and reduces the total area required for the fingerprint sensing system
3Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal, then the fingerprint identification accuracy is improved, but the production cost increases
Solution Approach 1:
The patent eliminates the ADC component from the bill of materials and manufacturing process. By generating digital signals directly through the dual DA converting units integrated into the sensing circuit, the invention removes the need to source, test, and assemble separate ADC components, thereby reducing production costs and simplifying manufacturing
Solution Approach 2:
The invention merges multiple functions (capacitance sensing and analog-to-digital conversion) into a single integrated circuit structure that can be manufactured as one monolithic device. This integration eliminates the need for multi-component assembly and reduces manufacturing complexity, leading to lower production costs while maintaining measurement precision
4Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal, then the fingerprint identification accuracy is improved, but the power consumption increases
Solution Approach 1:
The patent removes the power-hungry ADC component from the system. The dual DA converting units generate digital signals directly from the capacitance measurement without requiring the continuous high-power operation of an ADC, thereby significantly reducing the overall power consumption of the fingerprint sensing system while maintaining identification accuracy
Solution Approach 2:
The invention combines the low-power capacitance sensing operation with direct digital signal generation in a single integrated process. This merging eliminates the need for separate high-power conversion stages and enables the system to achieve accurate fingerprint identification with minimal power consumption throughout the sensing and conversion process
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 a simple, low-power, low-latency digital output related to touch capacitance, enhancing data security in fingerprint identification systems with reduced circuit complexity and cost, while maintaining accurate capacitance sensing.
Implementation Method 1
an integrating circuit, comprising an integrating input terminal, coupled to the touch capacitance, wherein the integrating input terminal receives an input voltage; and an integrating output terminal, configured to output an output voltage
Implementation Method 2
a comparator, comprising a first input terminal, coupled to the integrating output terminal; and a second input terminal, configured to receive a reference voltage;
Implementation Method 3
a positive digital-to-analog (DA) converting unit, coupled to the integrating input terminal; a negative DA converting unit, coupled to the integrating input terminal
Data Source
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AI summary
The present application provides a capacitance sensing circuit, comprising an integrating circuit, comprising an integrating input terminal, coupled to the touch capacitance , wherein the integrating input terminal receives an input voltage; and an integrating output terminal, configured to output an output voltage; a comparator ; a positive digital-to-analog (DA) converting unit; a negative DA converting unit; a control circuit, configured to control the positive DA converting unit and the negative DA converting unit; and a logic circuit, configured to output an output code, wherein the output code is related to a capacitance of the touch capacitance.