Method and system for determining body impedance
A method and system for determining a body impedance (Z body ) of a user are disclosed. The method comprises coupling a sensor device to the user, wherein the sensor device includes at least a first and a second electrode. The method includes applying a voltage signal (V in ) through a first impedance (Z in1 ) to the first electrode and through a second impedance (Z in2 ) to the second electrode to produce an output signal. The method includes measuring a differential voltage (V body ) across the first and second electrodes and calculating the body impedance (Z body ) using the measured differential voltage (V body ), the voltage signal (V in ), the first impedance (Z in1 ), and the second impedance (Z in2 ).
1. A method for determining a bio-impedance of a user, comprising:
measuring a first voltage across a first impedance after performing a first mixing operation using a clock signal or sine wave;
measuring a second voltage across the first impedance after performing a second mixing operation using a 90-degree phase shifted clock signal or cosine wave;
measuring a third voltage at an output after performing a third mixing operation using the clock signal or sine wave;
measuring a fourth voltage at the output after performing a fourth mixing operation using the 90-degree phase shifted clock signal or cosine wave; and
processing the measured first through fourth voltages and the first impedance to at determine a bio-impedance.
2. The method of claim 1 , wherein the cosine wave includes a 90-degree phase shifted from the sine wave.
3. The method of claim 1 , wherein the first mixing process and the second mixing process are performed sequentially via a mixer using a single path to avoid an offset correction.
4. The method of claim 1 ,
wherein the first or the third voltage is multiplied by a first clock signal to generate a first or third output, respectively, and
wherein the second or the fourth voltage is multiplied by the 90-degree phase shifted clock signal from the first clock signal to generate a second or fourth output, respectively.
5. The method of claim 4 , wherein the multiplication uses a same multiplier and a same path and the first through fourth mixing operations are performed sequentially in time.
6. The method of claim 1 , wherein the processing comprises:
filtering the measured first through fourth voltages;
digitizing the measured first through fourth voltages;
processing the measured first through fourth voltages to remove at least one of noise or artifacts; and
mathematically combining the measured first through fourth voltages using an operation including at least one of: addition, subtraction, multiplication, or division with each other and coefficients.
7. The method of claim 6 , wherein the filtering is performed by a low pass filter that performs at least one of: analog filtering, analog equalization, or amplification.
8. The method of claim 6 , wherein the processing the output signal includes performing at least one of:
digital filtering using a decimation filter,
digital equalizing,
digital amplification,
artifact removal,
baseline wander removal, or
mathematically combining the measured first through fourth voltages using an operation including at least one of: addition, subtraction, multiplication, or division with each other and coefficients.
9. The method of claim 6 , further comprising processing the output using user information including at least one of age, height, race, diet, weight, gender, or distance between the first and second electrode.
10. A bio-impedance front-end system, comprising:
a bio-impedance front-end receiver that:
performs a first mixing operation using a clock signal or sine wave,
performs a second mixing operation using a 90-degree phase shifted clock signal or cosine wave,
performs a third mixing operation using the clock signal or sine wave, and
performing a fourth mixing operation using the 90-degree phase shifted clock signal or cosine wave; and
a sensor device that:
measures a first voltage across a first impedance after the first mixing operation,
measures a second voltage across the first impedance after the second mixing operation,
measures a third voltage at an output after the third mixing operation using the clock signal or sine wave, and
measures a fourth voltage at the output after the fourth mixing operation using the 90-degree phase shifted clock signal or cosine wave; and
wherein the bio-impedance front-end receiver processes the measured first through fourth voltages and the first impedance to calculate a bio-impedance.