Acoustic Fingerprint Sensor with Isolated Drive and Sense Circuits
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Solution Overview
Problem
High-precision biometric sensors in electronic devices face challenges due to smaller component sizes, which result in lower signal quality and increased susceptibility to interference, requiring advanced signal processing that increases power consumption and processing delays, making them difficult to implement in devices with limited resources.
Innovation Solution
The implementation of an acoustic fingerprint imaging system with a high voltage drive circuit and a low voltage sense circuit, where the sense circuit is isolated from the drive circuit, allowing for safe operation and reducing interference sensitivity, using piezoelectric elements to generate and detect ultrasonic signals, and a controller to manage voltage biases to prevent damage from high voltage exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the size of imaging sensors is reduced to achieve high precision, then measurement precision is improved, but signal quality deteriorates and susceptibility to interference increases
Solution Approach 1:
The sensor is divided into multiple independently controllable sensing elements arranged in a grid pattern, allowing selective activation and independent signal processing for each element, which maintains signal quality while achieving high precision through spatial resolution
Solution Approach 2:
The system dynamically adjusts the operating state of sensing elements, activating only necessary elements for each measurement task, thereby maintaining high precision while reducing overall signal interference and power consumption
2Measurement precision
If advanced signal processing capability is added to compensate for lower signal quality, then measurement precision is improved, but power consumption increases
Solution Approach 1:
Signal processing is performed in stages, with preliminary filtering and conditioning applied at the sensing element level before signal aggregation, reducing the computational burden and power consumption of subsequent processing while maintaining precision
Solution Approach 2:
Multiple sensing elements are combined to form a composite signal, allowing spatial averaging and interference cancellation that reduces the need for complex post-processing while maintaining high measurement precision
3Power
If high voltage is applied to piezoelectric elements for driving, then acoustic signal generation is improved, but risk of damage to low voltage circuitry increases
Solution Approach 1:
The circuit is segmented into high voltage drive circuitry and low voltage sense circuitry, with electrical isolation between the two sections, allowing high power drive signals while protecting low voltage components from damage
Solution Approach 2:
A high voltage switch or transformer acts as an intermediary between the low voltage control circuitry and the high voltage piezoelectric elements, enabling safe voltage transformation and isolation to protect sensitive components
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 configuration enables high-resolution acoustic imaging with reduced interference sensitivity and power-efficient operation, allowing for effective biometric authentication in devices with limited resources while maintaining signal quality.
Implementation Method 1
an acoustic element configured to produce an acoustic pulse in response to an electronic activation signal and including at least an ultrasonic transducer
Implementation Method 2
a sense circuit coupled to the low voltage node and configured to obtain a low voltage electronic signal from the ultrasonic transducer
Data Source
AI summary
An acoustic fingerprint imaging system having a plurality of acoustic elements, each acoustic element including a transducer, and independent drive and sense circuitry is disclosed. Drive circuitry may require higher voltage than low voltage sense circuitry. Many embodiments described herein include a ground shifting controller to apply a voltage bias to the low voltage sense circuitry during a drive operation, in order to prevent electrical damage to the sense circuitry.