Apparatus for measuring electrical impedance
View Patent ↗The present invention provides an apparatus for measuring electrical impedance comprising: two input electrodes contacted to a subject for measuring impedance; a difference amplifier to which two signals inputted to the two input electrodes are inputted; a device for extracting a common mode component of two signals inputted to the two input electrodes; the third electrode contacted to the subject for measuring impedance; the first multiplier to which the common mode component is inputted; the first filter coupled with the first multiplier; the second multiplier coupled with the first filter; wherein a feedback signal outputted from the second multiplier is inputted to the third electrode.
1. An apparatus for measuring electrical impedance, comprising:
two input electrodes contacted to a subject for measuring impedance;
a difference amplifier to which two signals inputted to the two input electrodes are inputted;
a device for extracting a common mode component of the two signals inputted to the two input electrodes;
the third electrode contacted to the subject for measuring impedance;
the first multiplier to which the common mode component is inputted;
the first filter coupled with the first multiplier; and
the second multiplier coupled with the first filter such that the first and second multipliers and the first filter are in series;
wherein a feedback signal outputted from the second multiplier is inputted to the third electrode.
2. The apparatus for measuring electrical impedance of claim 1 , wherein the second multiplier is a variable gain amplifier.
3. The apparatus for measuring electrical impedance of claim 1 , wherein the first filter is a low pass filter.
4. The apparatus for measuring electrical impedance of claim 1 , wherein a filter is added between the output terminal of the second multiplier and the third electrode.
5. The apparatus for measuring electrical impedance of claim 1 , wherein the apparatus further comprises:
the third multiplier to which the common mode component is inputted;
the second filter coupled with the third multiplier;
the fourth multiplier coupled with the second filter; and
a device for combining a signal outputted from the fourth multiplier and a signal outputted from the second multiplier;
wherein a feedback signal outputted from the device for combining signals is inputted to the third electrode.
6. The apparatus for measuring electrical impedance of claim 5 , wherein a phase difference between an I signal inputted to the second multiplier and that of a Q signal inputted to the fourth multiplier is 90 degrees.
7. The apparatus for measuring electrical impedance of claim 1 , wherein the apparatus comprises a plurality of electrode pairs, and a multiplexer for changing the electrode pairs.
8. The apparatus for measuring electrical impedance of claim 7 , wherein the apparatus is applied to measuring body fat.