Bio-impedance measurement using voltage to current conversion

Patent metadata

Field	Value
Publication number	US-12458243-B2
Application number	US-202117523766-A
Country	US
Kind code	B2
Filing date	Nov 10, 2021
Priority date	Nov 10, 2021
Publication date	Nov 4, 2025
Grant date	Nov 4, 2025

Abstract

A method and apparatus are described for bio-impedance measurement using voltage to current conversion. In one example, a bio-impedance transducer includes an input stage to receive a bio-impedance signal having an oscillating voltage from two electrodes, the electrodes being coupled to a body, a resistance across the two electrodes to determine an alternating current of the bio-impedance signal, a gain stage coupled to the resistance to amplify the alternating current, a down converter coupled to the gain stage to convert the amplified alternating current to a direct current bio-impedance signal, and an analog-to-digital converter coupled to the down converter to convert the direct current bio-impedance signal to a digital bio-impedance signal.

First claim

What is claimed is:

1 . A bio-impedance transducer comprising:
an input stage configured to receive a bio-impedance signal having an oscillating voltage from two electrodes, the electrodes configured to be coupled to a body; a resistance across the two electrodes configured to determine an alternating current of the bio-impedance signal; a gain stage coupled to the resistance configured to amplify the alternating current; a down converter coupled to the gain stage configured to convert the amplified alternating current to a direct current bio-impedance signal; and an analog-to-digital converter coupled to the down converter configured to convert the direct current bio-impedance signal to a digital bio-impedance signal.

2 . The bio-impedance transducer of claim 1 , wherein the input stage comprises a source-follower circuit coupled to the electrodes at a first input and coupled to the resistance at a first output.

3 . The bio-impedance transducer of claim 1 , wherein the input stage comprises a feedback loop coupled across the electrodes and to the gain stage.

4 . The bio-impedance transducer of claim 3 , wherein the feedback loop includes a balanced operational transconductance amplifier.

5 . The bio-impedance transducer of claim 3 , wherein the feedback loop includes diode-connected transistors between the electrodes and the gain stage.

6 . The bio-impedance transducer of claim 1 , further comprising an excitation current source coupled to the electrodes configured to generate an alternating current excitation current to be injected into the body through the electrodes.

7 . The bio-impedance transducer of claim 6 , wherein the down converter comprises a mixer configured to mix the amplified alternating current with the excitation current.

8 . The bio-impedance transducer of claim 7 , wherein the analog-to-digital converter comprises a continuous time second order sigma delta analog-to-digital converter.

9 . The bio-impedance transducer of claim 8 , wherein the continuous time sigma delta analog-to-digital converter comprises a balanced operational transconductance amplifier coupled to the mixed amplified alternating current as an input and a capacitance coupled across the input and an output of the balanced operational transconductance amplifier.

10 . The bio-impedance transducer of claim 1 , wherein the gain stage comprises:
an in-phase gain stage coupled to the resistance configured to amplify an in-phase component of the alternating current; and a quadrature phase gain stage coupled to the resistance configured to amplify a quadrature phase component of the alternating current.

11 . The bio-impedance transducer of claim 10 , wherein the down converter comprises:
an in-phase down converter coupled to the in-phase gain stage configured to convert the amplified in-phase component to a direct current in-phase bio-impedance signal; and a quadrature phase down converter coupled to the quadrature phase gain stage configured to convert the amplified quadrature phase component to a direct current quadrature phase bio-impedance signal.

12 . The bio-impedance transducer of claim 11 , wherein the analog-to-digital converter comprises:
an in-phase analog-to-digital converter coupled to the in-phase gain stage configured to convert the direct current in-phase bio-impedance signal to a digital in-phase bio-impedance signal; and a quadrature phase analog-to-digital converter coupled to the quadrature phase down converter configured to convert the direct current quadrature phase bio-impedance signal to a digital quadrature phase bio-impedance signal.

13 . The bio-impedance transducer of claim 1 , further comprising a current mirror coupled to the down converter configured to convert a differential current from the down converter to a single ended current to the analog-to-digital converter.

14 . A method comprising:
receiving a bio-impedance signal, from two electrodes coupled to a human body, at an input stage, wherein the bio-impedance signal is an oscillating voltage; determining an alternating current of the bio-impedance signal based upon a known resistance that is coupled across the two electrodes; amplifying the alternating current using a gain stage circuit; converting the amplified alternating current to a direct current bio-impedance signal using a down converter coupled to the gain stage circuit; and converting the direct current bio-impedance signal to a digital bio-impedance signal using an analog-to-digital converter; wherein the digital bio-impedance signal corresponds to a health parameter of the human body.

15 . The method of claim 14 , further comprising:
feeding back the amplified alternating current; and amplifying the alternating current using a current mirror.

16 . The method of claim 14 , further comprising:
generating an alternating current excitation current from an excitation current source; and injecting the excitation current into the body through the electrodes.

17 . The method of claim 16 ,
wherein converting the amplified alternating current includes mixing the amplified alternating current with the excitation current.

18 . A health monitor system comprising:
an input stage configured to receive a bio-impedance signal having an oscillating voltage from two electrodes, the electrodes configured to be coupled to a body; a resistance across the two electrodes configured to determine an alternating current of the bio-impedance signal; a gain stage coupled to the resistance configured to amplify the alternating current; a down converter coupled to the gain stage configured to convert the amplified alternating current to a direct current bio-impedance signal; an analog-to-digital converter coupled to the down converter configured to convert the direct current bio-impedance signal to a digital bio-impedance signal; and a radio frequency system configured to send the digital bio-impedance signal to external components.

19 . The health monitoring system of claim 18 , wherein the input stage is based on a current balancing instrumentation amplifier such that the oscillating voltage from the electrodes appears on the resistance through a source follower input stage.

20 . The health monitoring system of claim 18 , wherein the input stage is coupled directly to the gain stage with no intermediate stage.

Assignees

• Nxp Bv

Inventors

• Kamran Muhammad
• Neuteboom Harry
• Ligouras Costantino
• Rueda Gómez Sergio Andrés
• Kroekenstoel Dave Sebastiaan
• Meijer Rinze Ida Mechtildis Peter

Classifications

• H04L67/12

  specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks · CPC title

• H03M3/40

  Arrangements for handling quadrature signals, e.g. complex modulators · CPC title

• H03F2200/261

  Amplifier which being suitable for instrumentation applications · CPC title

• H03F1/342

  in field-effect transistor amplifiers · CPC title

• A61B5/30

  Input circuits therefor · CPC title