Device for measuring impedance of biologic tissues including an alternating current (AC) coupled voltage-to-current converter

A device for measuring impedance of biological tissue comprising:

• a pair of electrodes for contacting the biological tissue;
• a voltage-to-current converter coupled to said pair of electrodes and configured to drive an alternating current (AC) through the biological tissue and to sense an AC voltage, said voltage-to-current converter comprising
• an amplifier having a first input, a second input, and an output, said amplifier coupled to said pair of electrodes,
• a current limiting resistor coupled to said second input, and
• a bypass capacitor coupled to the second input of said amplifier and in parallel with said current limiting resistor;
• and
• at least one single-ended amplitude modulation (AM) demodulator configured to demodulate the AC voltage and to generate a corresponding output voltage representing the impedance.

A device for measuring impedance of biological tissue comprising:

• a pair of electrodes for contacting the biological tissue;
• a voltage-to-current converter coupled to said pair of electrodes and configured to drive an alternating current (AC) through the biological tissue and to sense an AC voltage, said voltage-to-current converter comprising
• an amplifier having a first input, a second input, and an output, said amplifier coupled to said pair of electrodes,
• a first resistive voltage divider coupled to the first input,
• a second resistive voltage divider coupled to the second input, and
• a direct current (DC) filter capacitor coupled between the output of said amplifier and said second resistive voltage divider,
• wherein for a given working frequency of said amplifier, values of said first and second resistive voltage dividers and said DC filter capacitor are chosen according to:
• ω
• 0
• =
• ω
• p
• k
• 2
• ⁢
• R
• 3
• ⁢
• C
• =
• ω
• GBP
• k
• 1
• ⁢
• k
• 2
• ⁢
• R
• 3
• ⁢
• C
• wherein ω0 is the given working frequency, R3 is a resistive value of a first resistor of said second resistive voltage divider, C is a value of said DC filter capacitor, k2=1+((R4a+R4b)/R3) wherein R4a and R4b are respective resistive values of second and third resistors of said second resistive voltage divider, and ωGBPωpk1 is a gain-bandwidth product of said amplifier, wherein k1=1+(R2/R1), and wherein R1 and R2 are respective resistive values of first and second resistors of said first resistive voltage divider;
• and
• at least one single-ended amplitude modulation (AM) demodulator configured to demodulate the AC voltage and to generate a corresponding output voltage representing the impedance.

A method of measuring impedance of biological tissue comprising:

• driving an AC current through biological tissue via two electrodes to be placed in contact with the biological tissue using a voltage-to-current converter comprising an amplifier having a first input, a second input, and an output, the amplifier coupled to the pair of electrodes, a current limiting resistor coupled to the second input, and a bypass capacitor coupled to the second input of the amplifier and in parallel with the current limiting resistor;
• sensing an AC voltage through the biological tissue via the two electrodes using the voltage-to-current converter;
• using at least one single-ended AM demodulator to demodulate the AC voltage and to generate a baseband voltage representing the impedance;
• and
• generating output signals representative of DC and AC components of the baseband voltage.