Fingerprint Sensing System Non-Linear ADC

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Solution Overview

Problem

Fingerprint sensors face challenges in accurately capturing fingerprints due to high computational resource and power consumption requirements, especially in resource-constrained systems, where linearization of measurement results is time-consuming and often impossible, and high-resolution analog-to-digital converters are needed for sufficient image quality.

Innovation Solution

A fingerprint sensing system utilizing a non-linear analog-to-digital converter with a logarithmic conversion function, combined with a lookup table, to reduce computational resources and power consumption, enabling efficient linearization of measurement results while maintaining image quality with lower resolution sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a high-resolution analog-to-digital converter is used to capture sufficient image quality, then measurement precision is improved, but computational resources and power consumption increase

Engineering Contradiction:

Improveimage qualityVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent applies parameter changes by implementing a non-linear conversion function (specifically logarithmic) in the analog-to-digital converter. This transforms the linear relationship between capacitance and digital output into a non-linear one, where the conversion ratio dynamically adjusts based on the input signal level. This allows the system to achieve sufficient measurement precision for fingerprint capture while using lower resolution sensors, thereby reducing power consumption and computational requirements

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional approach by using a non-linear (logarithmic) conversion function instead of a linear one. This inversion allows the system to compress the dynamic range of sensor outputs, enabling lower resolution ADCs to effectively capture the necessary fingerprint details without requiring high computational resources for linearization processing

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If linearization of measurement results is performed to improve accuracy, then measurement precision is improved, but processing time increases

Engineering Contradiction:

ImproveaccuracyVSAvoidprocessing time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies preliminary action by pre-computing and storing the non-linear conversion characteristics in a lookup table during system initialization or manufacturing. The analog-to-digital converter directly uses this pre-prepared conversion data, eliminating the need for real-time linearization calculations. This allows the system to achieve accurate measurement results without time-consuming processing during fingerprint capture operations

Inventive Principle:

Principle #10Preliminary action

3Productivity

If computational resources are reduced to improve system efficiency, then productivity is improved, but measurement precision deteriorates

Engineering Contradiction:

Improvesystem efficiencyVSAvoidfingerprint detection accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent replaces the mechanical/computational system of high-resolution ADCs with extensive linearization processing with a streamlined non-linear conversion approach. By using a logarithmic conversion function with pre-computed lookup tables, the system eliminates complex real-time calculations while maintaining measurement precision. This substitution achieves both high productivity through reduced computational requirements and accurate fingerprint detection

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system achieves efficient fingerprint detection with reduced computational resources and power consumption, allowing for accurate fingerprint capture even with lower resolution sensors, thereby improving the feasibility in resource-constrained systems.

Implementation Method 1

Each sensing cell may have a physical property that may change in response to the proximity of an external object, for instance a human finger. In this example, the physical property of the sensing cell is an electrical capacitance that may change in dependence on the distance between the upper surface of the sensing cell and the surface of a human finger

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentEP3267358B1Fingerprint sensing system and method

Publication Date: 2021.10.13 NXP BV

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AI summary

According to a first aspect of the present disclosure, a fingerprint sensing system is provided, comprising: a sensing unit configured to measure a physical property of a sensing cell and to produce a voltage in dependence on said physical property; and an analog-to-digital converter configured to convert said voltage into a digital signal, wherein said analog-to-digital converter implements a non-linear conversion function. According to a second aspect of the present disclosure, a corresponding fingerprint sensing method is conceived. According to a third aspect of the present disclosure, a corresponding computer program product is provided.