Capacitance Sensing Circuit With Direct Digital Output for Fingerprint ID
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Solution Overview
Problem
Conventional fingerprint identification systems using capacitance sensing circuits face high circuit complexity, large area occupation, high production costs, and high power consumption due to the need for analog-to-digital converters to convert analog voltage signals into digital signals.
Innovation Solution
A capacitance sensing circuit that directly converts touch capacitance into a digital signal using an integrating circuit, comparator, positive and negative digital-to-analog converting units, and a logic circuit, eliminating the need for analog-to-digital converters, with a control circuit adjusting input voltage to generate output codes related to capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal into digital signals, then the fingerprint identification can be performed, but the circuit complexity increases, circuit area occupied increases, production cost increases, and power consumption increases
Solution Approach 1:
The patent extracts and eliminates the ADC component from the traditional capacitance sensing circuit. Instead of using an ADC to convert analog voltage signals to digital signals, the invention directly outputs digital signals from the capacitance sensing circuit, thereby removing the source of high circuit complexity, large area occupation, high production cost, and high power consumption associated with ADCs.
Solution Approach 2:
The patent replaces the conventional analog signal processing mechanism (ADC conversion) with a direct digital output mechanism. The capacitance sensing circuit directly generates digital signals without requiring analog-to-digital conversion, substituting the traditional mechanical/electrical conversion system with a more efficient direct digital generation approach.
2Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal into digital signals, then the fingerprint identification can be performed, but the circuit area occupied increases
Solution Approach 1:
The patent extracts and eliminates the ADC component from the traditional capacitance sensing circuit. Instead of using an ADC to convert analog voltage signals to digital signals, the invention directly outputs digital signals from the capacitance sensing circuit, thereby removing the source of high circuit complexity, large area occupation, high production cost, and high power consumption associated with ADCs.
3Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal into digital signals, then the fingerprint identification can be performed, but the production cost increases
Solution Approach 1:
The patent extracts and eliminates the ADC component from the traditional capacitance sensing circuit. Instead of using an ADC to convert analog voltage signals to digital signals, the invention directly outputs digital signals from the capacitance sensing circuit, thereby removing the source of high circuit complexity, large area occupation, high production cost, and high power consumption associated with ADCs.
4Measurement precision
If an analog-to-digital converter (ADC) is used to convert the analog voltage signal into digital signals, then the fingerprint identification can be performed, but the power consumption increases
Solution Approach 1:
The patent extracts and eliminates the ADC component from the traditional capacitance sensing circuit. Instead of using an ADC to convert analog voltage signals to digital signals, the invention directly outputs digital signals from the capacitance sensing circuit, thereby removing the source of high circuit complexity, large area occupation, high production cost, and high power consumption associated with ADCs.
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 results in a simple circuit design with reduced area, low power consumption, and low latency, effectively converting capacitance into digital signals for fingerprint identification.
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
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.