Passive Filter Impedance Matching for Low-Power Wake-Up Detection

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Solution Overview

Problem

Battery-operated radio sensor nodes in wireless sensor networks face high power draw even in quiescent states due to the continuous operation of components like operational amplifiers, leading to short battery life and increased maintenance costs, especially in hard-to-reach locations.

Innovation Solution

A passive filter stage with an LC resonant circuit and a quartz or microacoustic resonator is used to match the output impedance of the rectifier circuit to the input impedance of the detection device, reducing power consumption by attenuating noise and interference signals and allowing the detection device to operate efficiently at lower frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the operational amplifier is kept in constant operation to enable waking at any time, then the appliance can be woken reliably, but the current draw increases significantly

Engineering Contradiction:

Improvewaking reliabilityVSAvoidcurrent draw

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system is divided into two functional segments: a passive filter stage that remains continuously active to detect wake-up signals, and the main detection device (microcontroller) that operates in low-power quiescent mode. This segmentation allows the detection function to be separated from the high-power processing function, enabling reliable wake-up detection while minimizing overall power consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A passive filter stage with LC resonant circuit is introduced as an intermediary between the antenna and the detection device. This intermediary component performs preliminary signal processing and filtering in the analog domain, allowing the detection device to remain in low-power state while still being able to detect wake-up signals when activated.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Difficulty of detecting and measuring

If the detection device operates at higher frequencies to process all signals, then signal detection capability is improved, but power consumption increases

Engineering Contradiction:

Improvesignal detection capabilityVSAvoidpower consumption

Core Design Contradiction:

Difficulty of detecting and measuringVSUse of energy by moving object

Solution Approach 1:

The passive filter stage performs preliminary signal processing and frequency selection before signals reach the detection device. By pre-filtering signals in the analog domain and selecting only relevant frequency bands, the detection device only needs to process pre-processed signals at lower frequencies, reducing its power consumption while maintaining detection capability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system replaces active electronic signal processing (which would require powered components operating at high frequencies) with passive analog filtering using LC resonant circuits. This substitution eliminates the need for the detection device to actively process high-frequency signals, significantly reducing power consumption while preserving signal detection functionality.

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

This solution significantly reduces the current draw of the detection device while maintaining a long radio range, enabling extended battery life and lower maintenance costs by minimizing power consumption during quiescent states.

Implementation Method 1

the filter and/or the filter stage has or have an LC resonant circuit

Methodology Applied

Scientific EffectLC resonant circuit: Resonance

Implementation Method 2

having a quartz oscillator and/or a microacoustic resonator

Methodology Applied

Scientific EffectQuartz oscillator: Piezoelectric Effect

Implementation Method 3

having a quartz oscillator and/or a microacoustic resonator

Methodology Applied

Scientific EffectMicroacoustic resonator: Surface Acoustic Wave

Implementation Method 4

the output of the rectifier circuit and the detection device have a passive filter arranged between them which passes the modulation signal

Methodology Applied

Scientific EffectPassive filtering: Filter (electronic)

Data Source

PatentUS8958766B2Electronic device comprising an operating mode switching unit

Publication Date: 2015.02.17 ENDIIO ENG GMBH

AI summary

An electronic appliance comprising an electrical circuit and an operating mode switching unit which can be awakened out of a sleep state into a working state in which the current consumption of the circuit is greater in than in the sleep state. To receive a radio signal, the appliance has a receiver comprising a UHF carrier that is amplitude-modulated by a modulation signal. The receiver comprises a UHF antenna connected to a passive filter stage to an input of a passive rectifier circuit. An output of the rectifier circuit is connected to a detector for the modulation signal. To wake the electrical circuit from the sleep state, the operating mode switching unit has a control connection to the detector. The appliance has a low current draw in the sleep state by matching the output impedance of the rectifier circuit to the input impedance of the detector.