Bioimpedance Measurement Using Differential AM Demodulation

Solution Overview

Problem

Existing bioimpedance measurement devices require large bandwidth instrumentation amplifiers or low frequency currents due to the need for input amplification of modulated signals, limiting their power consumption and suitability for wearable applications.

Innovation Solution

A device with differential amplitude modulation demodulators connected directly to electrodes, using square-wave carriers to generate base-band signals representing the real and imaginary parts of bioimpedance, allowing for low-cost, low-power amplification and accurate impedance estimation without the need for high bandwidth amplifiers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If input amplification of modulated signals is performed using instrumentation amplifiers, then measurement precision is improved, but power consumption increases and device complexity increases

Engineering Contradiction:

Improvebioimpedance measurement precisionVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent applies preliminary action by performing demodulation of the modulated bioimpedance signal before amplification. The AM demodulator converts the high-frequency modulated signal into a baseband signal, which can then be amplified using low-power, narrow-bandwidth amplifiers. This reordering of operations (demodulate first, then amplify) resolves the contradiction by enabling precise measurement without requiring high-power wide-bandwidth amplifiers.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the conventional instrumentation amplifier approach with an electronic signal processing substitution. Instead of using complex instrumentation amplifiers to handle modulated signals directly, the system substitutes this with an AM demodulator followed by simple amplification stages, achieving the same measurement precision with much lower power consumption and device complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If large bandwidth instrumentation amplifiers are used to amplify modulated signals, then measurement precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvebioimpedance measurement precisionVSAvoidamplifier bandwidth requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by performing demodulation of the modulated bioimpedance signal before amplification. The AM demodulator converts the high-frequency modulated signal into a baseband signal, which can then be amplified using low-power, narrow-bandwidth amplifiers. This reordering of operations (demodulate first, then amplify) resolves the contradiction by enabling precise measurement without requiring high-power wide-bandwidth amplifiers.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the conventional instrumentation amplifier approach with an electronic signal processing substitution. Instead of using complex instrumentation amplifiers to handle modulated signals directly, the system substitutes this with an AM demodulator followed by simple amplification stages, achieving the same measurement precision with much lower power consumption and device complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If high frequency currents are used for bioimpedance measurement, then measurement precision is improved, but interference with electrical activity of nervous and muscular tissues increases

Engineering Contradiction:

Improveimpedance measurement accuracyVSAvoidinterference with nervous and muscular tissue activity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary approach by using amplitude modulation as a carrier mechanism. Instead of directly measuring high-frequency currents that interfere with tissue activity, the system modulates a high-frequency carrier signal with the bioimpedance information, then demodulates it to recover the measurement. This intermediary modulation-demodulation process allows accurate measurement while using lower amplitude currents that don't interfere with nervous and muscular tissue activity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10660540B2Method and device for measuring electrical impedance of biological tissues

Publication Date: 2020.05.26 STMICROELECTRONICS SRL

AI summary

A device for measuring an electrical impedance of biologic tissue may include electrodes configured to contact the biologic tissue and generate a differential voltage thereon. The device may include a first circuit coupled to the electrodes and configured to force an oscillating input signal therethrough, and a differential amplitude modulation (AM) demodulator coupled to the plurality of electrodes. The differential AM demodulator may be configured to demodulate the differential voltage, and generate a base-band signal representative of the demodulated differential voltage. The device may further include an output circuit downstream from the differential AM demodulator and may be configured to generate an output signal representative of the electrical impedance as a function of the base-band signal.