Fingerprint Sensor Wake-on-Event Probing Circuit
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Solution Overview
Problem
Fingerprint sensors in mobile devices face challenges in managing power consumption efficiently, particularly when idle or waiting for user input, and require methods to quickly detect finger presence, which increases battery demand and device size.
Innovation Solution
The implementation of a 'wake-on-event' mode in fingerprint sensing circuits that uses probing signals and response pulses to detect finger activity by establishing reference signals and counting peak exceedances, allowing the circuit to conserve power and quickly wake up when activity is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fingerprint sensing circuits continuously monitor for finger presence, then detection speed is improved, but power consumption increases
Solution Approach 1:
The circuit alternates between active monitoring mode and low-power sleep mode, periodically waking up to check for finger presence using probing signals, then returning to sleep mode. This periodic operation maintains detection capability while significantly reducing average power consumption compared to continuous monitoring.
Solution Approach 2:
The circuit performs preliminary detection using low-power probing signals before activating the full fingerprint sensing algorithm. This preliminary action allows the system to quickly determine if a finger is present without committing full power resources, enabling faster response while conserving energy.
2Measurement precision
If fingerprint sensors use complex algorithms for accurate finger detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The detection process is divided into separate stages: initial probing signal transmission, response signal reception, peak detection, and threshold comparison. Each stage handles a specific aspect of detection, simplifying the overall circuit design while maintaining accuracy through systematic processing of detection signals.
Solution Approach 2:
Reference signals are introduced as intermediaries to facilitate accurate detection. By comparing response signals against predetermined reference signals, the circuit achieves precise finger presence detection without requiring complex algorithms, as the reference signals provide a stable baseline for comparison.
3Use of energy by moving object
If fingerprint sensors operate in low-power modes, then power consumption is reduced, but detection response time increases
Solution Approach 1:
When a probing signal detects a potential finger presence, the circuit rapidly transitions from sleep mode to active mode, skipping intermediate power states. This rushing through of power transition states minimizes the time spent in intermediate modes, reducing overall detection response time while maintaining low average power consumption.
Solution Approach 2:
The circuit performs preliminary checks using minimal power consumption to determine if full activation is necessary. By conducting initial probing operations in low-power mode and only fully activating when needed, the system reduces average power consumption while maintaining quick response capability for actual detection events.
Data Source
AI summary
An apparatus and method for detecting the presence of a finger on a fingerprint sensor is disclosed in one embodiment of the invention as including transmitting a probing signal, comprising a series of probing pulses, to a fingerprint sensing area. A response signal, comprising a series of response pulses, is received from the fingerprint sensing area in response to the probing signal. An upper reference signal is generated and finger activity is detected on the fingerprint sensing area by monitoring whether the peaks of the response pulses exceed the reference signal.