阅读说明：本技术 生物阻抗和接触阻抗测量 (Bioimpedance and contact impedance measurements ) 是由 J·C·C·安奥 J·卡尔皮玛拉维拉 L·P·赖尔登 于 2019-05-31 设计创作，主要内容包括：本公开涉及生物阻抗和接触阻抗测量。准确测量生物阻抗对于感知机体的特性是重要的。不幸的是,接触阻抗会显着降低生物阻抗测量的准确性。为了解决这个问题,可以配置用于实现四线阻抗测量的电路以进行多次电流测量。多次电流测量建立方程系统以允许导出未知的生物阻抗和接触阻抗。结果是精确的生物阻抗测量,其不受大接触阻抗的不利影响。而且,可以识别具有不期望的大阻抗的不良接触。(The present disclosure relates to bioimpedance and contact impedance measurements. Accurate measurement of bio-impedance is important for sensing properties of the body. Unfortunately, contact impedance can significantly reduce the accuracy of the bioimpedance measurement. To address this problem, a circuit for implementing four-wire impedance measurements may be configured to perform multiple current measurements. Multiple current measurements establish a system of equations to allow for the derivation of unknown bio-impedance and contact impedance. The result is an accurate bio-impedance measurement that is not adversely affected by large contact impedances. Also, a bad contact with an undesirably large impedance can be identified.)

1. A method of measuring impedance, comprising:

Forming unique signal paths, wherein each unique signal path includes at least some of the impedances, the unique signal paths include at least once each impedance, and the impedances include a bioimpedance and four branch impedances,

Making a current measurement of the unique signal path, an

Deriving the impedance based on the current measurement.

2. The method of claim 1, further comprising:

Deriving a voltage from a signal generator by applying the output of the signal generator to a resistor of known resistance and measuring the current through the resistor, an

The impedance is derived further based on a voltage from the signal generator.

3. The method of claim 1, wherein forming a signal path comprises:

A configurable network is controlled to connect an output of the signal generator to the unique signal path and to connect an input of a current measurement circuit to the unique signal path.

4. The method of claim 1, wherein making a current measurement comprises:

Applying a signal from a signal generator to the unique signal path, and

The current through each unique signal path is measured by a current measurement circuit.

5. The method of claim 1, wherein each distinct signal path includes two branch impedances.

6. The method of claim 1, wherein each of the some of the unique signal paths includes a bioimpedance and two branch impedances.

7. The method of claim 1, wherein each unique signal path comprises a network of all impedances.

8. A circuit for measuring impedance, comprising:

A signal generator for generating a signal at an output of the signal generator,

A current measurement circuit for measuring a current at an input of the current measurement circuit,

A configurable network for connecting the output of the signal generator to the input of the current measurement circuit via unique signal paths, wherein each unique signal path includes at least some of: bioimpedance and branch impedance, and

A digital circuit to determine the bio-impedance and the branch impedance based on a current measurement of the unique signal path.

9. The circuit of claim 8, wherein:

The configurable network connects the output of the signal generator to the input of the current measurement circuit via at least five distinct signal paths, an

The current measurement circuit measures the at least five current measurements.

10. The circuit of claim 9, wherein:

The digital circuit determines the bio-impedance and four branch impedances based on at least five current measurements of the unique signal path.

11. the circuit of claim 8, wherein the distinct signal path includes each of the bioimpedance and the branch impedance at least once.

12. The circuit of claim 8, wherein each distinct signal path includes two branch impedances.

13. The circuit of claim 8, wherein each of the some of the unique signal paths includes a bioimpedance and two branch impedances.

14. The circuit of claim 8, wherein each unique signal path includes a network of all bioimpedance and branch impedances.

15. The circuit of claim 8, wherein:

The configurable network further connects the output of the signal generator to the input of the current measurement circuit through a resistor having a known resistance value, an

The current measurement circuit further measures the current through the resistor to determine the voltage from the signal generator.

16. A circuit for measuring impedance, comprising:

Four branches each having four electrodes, wherein two of the four electrodes are connected to a first end of a bioimpedance and the other two of the four electrodes are connected to a second end of the bioimpedance,

Circuitry to apply signals to and make current measurements of at least five unique impedance networks, wherein each unique impedance network has at least two of the four branches,

Digital circuitry to derive the bio-impedance and the impedances of the four branches based on the current measurements.

17. The circuit of claim 16, wherein each distinct impedance network includes all four branches.

18. The circuit of claim 16, wherein the at least five unique impedance networks include unique impedance networks that: with one of the four branches connected to the signal generator and the other three of the four branches connected to the current measuring circuit.

19. The circuit of claim 16, wherein the at least five distinct impedance networks include a second distinct impedance network: with two of the four branches connected to the signal generator and the other two of the four branches connected to the current measuring circuit.

20. The circuit of claim 16, wherein:

The digital circuit determines contact qualities corresponding to the four electrodes based on the impedances of the four branches.

Technical Field

The present invention relates to the field of integrated circuits, and more particularly to impedance measurement.

Background

Impedance measurements of the body, referred to herein as bioimpedance, have many applications in healthcare and consumer applications. Impedance measurements may be made by electrodes or wearable devices (e.g., watches, chest bands, head bands, patches, etc.) provided in the fuselage-wear system. Circuitry coupled to the electrodes can derive an unknown impedance of the body in which the electrodes are placed. Impedance measurements are particularly useful for vital sign monitoring, sensing of tissue and fluid levels in the body, for detecting signs of pulmonary edema or for assessing body composition. Furthermore, electrical impedance tomography is an emerging non-invasive technique for medical imaging. Due to various challenges, making accurate bio-impedance measurements is not easy.

Drawings

For a more complete understanding of the present disclosure, and the features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, wherein like reference numerals represent like parts, in which:

FIG. 1 illustrates a system having electrodes and circuitry for performing one exemplary way of four-wire impedance measurement of manufacturing bioimpedance according to some embodiments of the present disclosure;

FIG. 2 illustrates input capacitances present in a circuit performing a four-wire impedance measurement of bio-impedance according to some embodiments of the present disclosure;

FIG. 3 illustrates current leakage present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of the present disclosure;

FIG. 4 illustrates calibration measurements according to some embodiments of the present disclosure;

5-9 illustrate five current measurements according to an embodiment of the present disclosure;

FIG. 10 illustrates the current leakage present in the measurements seen in FIG. 5, in accordance with some embodiments of the present disclosure;

11-15 illustrate five current measurements to avoid current leakage according to embodiments of the present disclosure; and

Fig. 16 is a flow chart illustrating a method for measuring impedance according to some embodiments of the present disclosure.

Detailed Description

Overview

Accurately measuring the bio-impedance is important for sensing the properties of the body. Unfortunately, contact impedance can significantly reduce the accuracy of the bioimpedance measurement. To address this problem, a circuit for implementing four-wire impedance measurements may be configured to perform multiple current measurements. Multiple current measurements establish a system of equations to allow the derivation of unknown bio-impedance and contact impedance. The result is an accurate bio-impedance measurement that is not adversely affected by large contact impedances. Also, a bad contact with an undesirably large impedance can be identified.

Four wire impedance measurement

One technique for impedance measurement is a four terminal sensing scheme or a four wire impedance measurement scheme. Sometimes it is referred to as kelvin sensing. This technique involves sensing or deriving an unknown bio-impedance using four electrodes placed on the body.

Fig. 1 illustrates a system 100 having electrodes and circuitry for performing one exemplary manner of generating a four-wire impedance measurement of bioimpedance, according to some embodiments of the present disclosure. In the figure, the unknown bioimpedance is shown as Z_{Machine body}. System 100 includes electrodes 104, 106, 108, and 110 (or contacts with the body). The electrodes 104, 106, 108 and 110 each have a contact impedance Z_E1、Z_E2、Z_E3And Z_E4. Contact impedance Z_E1、Z_E2、Z_E3And Z_E4representing the skin electrode impedance of electrodes 104, 106, 108, and 110, respectively. The circuit 150, packaged as an integrated circuit or chip, has pins (or connections) that connect to the electrodes. Pin CE0 is electrically coupled to electrode 104. Pin AIN2 is electrically coupled to electrode 106. Pin AIN3 is electrically coupled to electrode 108. Pin AIN1 is electrically coupled to electrode 110.

The system 100 has four branches: a branch including electrode 104 and pin CE0, a branch including electrode 106 and pin AIN2, a branch including electrode 108 and pin AIN3, and a branch including electrode 110 and pin AIN 1. Two branches for sensing unknown bio-impedance Z_{machine body}While the other two branches are used for sensing the unknown bio-impedance Z_{Machine body}The second end of (a). The branch including the electrode 104 is coupled to an unknown bioimpedance Z_{Machine body}The first end of (a). The branch comprising the electrode 106 is coupled to an unknown bioimpedance Z_{Machine body}The first end of (a). The branch including the electrode 108 is coupled to the unknown bioimpedance Z_{Machine body}The second end of (a). The branch including the electrode 110 is coupled to an unknown bioimpedance Z_{Machine body}The second end of (a). The four branches are connected to respective pins of the circuit 150. A portion of the branch external to the circuit 150 may represent a cable having a patch at the end of the cable. The portion of the branch external to the circuit 150 may also represent a conductor or wire having an electrode at the end of the conductor or wire. The conductors and electrodes may be mounted in a wearable device. Alternatively, C_ISO1、C_ISO2、C_ISO3、C_ISO4The illustrated capacitance may be included between each pair of electrodes and pins to provide isolation and protection (e.g., block DC signals) between the body of a human user and circuitry within the circuit 150.

The circuit 150 may include a multiplexer (mux) 112. Mux 112 may be controlled in a manner that connects the signal paths of different pins to different portions of circuit 150. As used herein, Mux 112 represents a configurable network that is controllable to connect different portions of circuit 150 to different pins. For example, the multiplexer 112 may connect different portions of the circuit 150 to different branches (branches with corresponding electrodes) connected to the pins. Different configurations of the multiplexer 112 may form different signal paths or different impedance networks (an impedance network is synonymous with a signal path).

The circuit 150 may include a signal generator 116 (e.g., a sinusoidal signal generator). The signal generator can generate peak voltage V_{Peak value}of the signal of (1). The signal generator being in the signal generatorThe output terminal generates a signal.

The circuit 150 may include a voltage measurement circuit 118 to measure the voltage across the positive and negative inputs of the voltage measurement circuit 118. In some embodiments, the voltage measurement circuit 118 may include an instrumentation amplifier (inAmp)120 having a positive terminal and a negative terminal for detecting a voltage difference between the positive and negative terminals and outputting a voltage output representative of the voltage difference. The voltage measurement circuitry 118 may include a Discrete Fourier Transform (DFT) block 122 and a summing block 124 to produce a voltage measurement based on the voltage output from the inAmp 120. The components used to generate the voltage measurement (e.g., the voltage difference between the two inputs) may vary depending on the implementation.

The circuit 150 may also include a current measurement circuit 126 to measure the current at the input of the current measurement circuit 126. In some embodiments, the current measurement circuit 126 may include a transimpedance amplifier (TIA)128 to convert a current at an input terminal of the TIA 128 into a voltage output representative of the current. The current measurement circuitry 126 may include a DFT block 130 and a summing block 132 to generate a current measurement based on the voltage output from the TIA 128. The components used to generate the current measurement (e.g., the amount of current flowing through the input) may vary depending on the implementation.

to make the impedance measurement, a voltage is generated across the unknown bioimpedance, shown as Z_{Machine body}. Unknown bioimpedance Z_{Machine body}The voltage at can be regarded as V_A-V_B. Unknown bioimpedance Z_{Machine body}The voltage on may be generated or applied by the signal generator 116. At the same time, the unknown bioimpedance Z_{Machine body}The voltage on is measured by the voltage measurement circuit 118 and passes through the unknown bio-impedance Z_{Machine body}May also be measured by current measurement circuit 126. The measured voltage and the measured current may be used to derive the unknown bio-impedance Z_{Machine body}The impedance value of (2). In particular, the unknown bioimpedance Z_{Machine body}Is related to the voltage measurement divided by the current measurement.

In conventional two-wire impedance measurement, the measurement problem may be due to the impedance of the cable (including contact impedance) being added to the impedance of the cableknown bio-impedance Z_{Machine body}thus corrupting the impedance measurement. For simplicity, the existing impedances are grouped together as the contact impedance in each branch. In theory, four-wire impedance measurements can avoid such problems. When the bio-impedance Z is unknown_{Machine body}far above the impedance of the cable, the measurement results may be sufficiently accurate.

In practice, however, four-wire impedance measurements may have certain other limitations or non-idealities that may significantly affect the accuracy of the bioimpedance measurements. These limitations may be significant, for example, when impedance measurements are made at low frequencies, high frequencies, certain frequencies, or various frequencies. In some cases, the contact impedance Z_E1、Z_E2、Z_E3And Z_E4May be greater than the unknown bio-impedance Z_{Machine body}. For example, mechanical and/or environmental causes (e.g., humidity, movement, hair on the skin, etc.) may result in poor contact and may severely increase one or more contact impedances. In some severe cases, the contact impedance may be greater than 2k Ω (amplitude). Optional capacitor C in some cases_ISO1、C_ISO2、C_ISO3、C_ISO4The impedance of the cable is also significantly increased or affected. In some cases, the contact impedance Z_E1、Z_E2、Z_E3and Z_E4May be unbalanced to each other (e.g., the imbalance may be greater than 1k Ω). These limitations have been found to reduce the accuracy of the four-wire impedance measurement.

One of the problems that arises is reducing the accuracy of the bioimpedance measurement, i.e., there may be a large input capacitance (e.g., about 40pF) at pin AIN2 and pin AIN3 fig. 2 shows the input capacitance present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of the present disclosure the ground input capacitance 202 may be present at pin AIN2 and the ground input capacitance 204 may also be present at pin AIN3 the ground input capacitance 202, contact impedance Z _E2 and capacitance C _ISO2 may form a filter, which filter may be problematic because the contact impedance Z _E2 is unknown and therefore the effect of the filter is also unknown, the ground input capacitance 204, contact impedance Z _E3 and capacitance C _ISO3 may also form another filter, this other filter may be problematic because the contact impedance Z8 is unknown and therefore the effect of this other filter is also negative, ideally, voltage V6 should be the same as voltage V _C, voltage V _B should be the same as voltage V29, and voltage V4624 may be different from the high voltage V4642, and the impedance of the contact impedance V4624 may be different from the high voltage V4624 and the impedance of the high voltage V465, which may be due to the impedance of the high impedance of the contact resistor 202 and the high impedance of the high impedance V465 and the impedance of the contact resistor 202 and the impedance of the impedance range of the contact resistor 202 which may be observed under the range of the high impedance of the contact resistor 46v _A.

Another problem that may reduce the accuracy of the bio-impedance measurement is current leakage. Fig. 3 illustrates current leakage present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of the present disclosure. The current leakage occurs because of the impedance Z of the branch with the electrode 108_S-May be similar to the impedance Z of the branch with the electrode 110 driving the TIA 128_F-. This results in a flow through unknown bio-impedance Z_{Machine body}Some of current I of_{Machine body}Flows through the branch with the electrode 108, and not all of the current I_{Machine body}Will flow through the branch with the electrode 110. In other words, the current I through the branch with the electrode 108_ZS-Ideally zero, and the current I through the branch with the electrode 110_ZF-Ideally equal to the current I_{Machine body}. In fact, the current I_ZS-Is not zero. As a result, the current I through the branch with the electrode 110_ZF-Is not equal to current I_{Machine body}And the current measuring circuit 126 does not measure the current I_{Machine body}A part of (a). The current measurement is destroyed, so the impedanceThe measurement is also corrupted. The high contact resistance of the branch mechanism can exacerbate this problem.

Exemplary scheme for deriving contact impedance through multiple measurements and signal processing

By configuring the multiplexer 112 and taking a plurality of current measurements, the (unknown) impedance of the system, including the unknown bio-impedance Z, can be derived_{machine body}And contact impedance Z_E1、Z_E2、Z_E3And Z_E4Based on a system of equations. The system of equations is formed by the calibration measurements and several other current measurements for different signal paths are formed by the configuration multiplexer 112. The multiplexer 112 may selectively couple the output of the signal generator 116 and the input of the current measurement circuit 126 to different pins (e.g., RCAL1, RCAL2, CE0, AIN2, AIN3, and AIN 1). Thus, the multiplexer 112 may connect the output of the signal generator 116 to the input of the current measurement circuit 126 through a different signal path or a different impedance network involving at least some unknown impedance. The different signal paths individually may include two or more unknown impedances of the system: unknown bioimpedance Z_{Machine body}And contact impedance Z_E1、Z_E2、Z_E3And Z_E4. The unique signal path or unique impedance network of at least some unknown impedances, and the current measurements of the unique signal path or unique impedance network, establish a system of equations for the unknown impedances. The unique signal path or unique impedance network together includes each of the at least one unknown impedance. Each unique signal path or unique impedance network will include at least some unknown impedance of the system. Effectively, the signal generator 116 may excite the unique signal path or unique impedance network formed by the multiplexer 112, and the current measurement circuit 126 may measure the current through the unique signal path or unique impedance network.

To determine five unknown impedances (bio-impedance and four contact impedances), at least five equations are required. With a sufficient number of equations, five unknown impedances can be derived by signal processing (i.e., calculation). By appropriate processing, the current measurement allows determination of the bio-impedance and the contact impedance. The current measurement may be performed by the current measurement circuit 126. The signal processing may be performed in the digital domain, for example, by digital circuitry 190. Digital circuitry 190 may include dedicated digital hardware to perform signal processing. Digital circuitry 190 may include a microprocessor or microcontroller configured to execute instructions that implement signal processing. Digital circuitry 190 may be provided on-chip with circuitry 150 or off-chip (as shown). Digital circuit 190 may be implemented to control multiplexer 112 to form a unique signal path or a unique impedance network from signal generator 116 to current measurement circuit 126. The computer readable memory 192 may store the measured values. Computer readable memory 192 may store instructions that implement signal processing. Computer-readable memory 192 may be provided on-chip with circuitry 150 or off-chip (as shown).

_{CAL CAL CAL CAL CAL CAL}FIG. 4 illustrates a calibration measurement according to some embodiments of the present disclosure. the calibration measurement is performed to determine the peak voltage from the signal generator 116 (if not already measured or if not yet known). the system of equations formed by the current measurements through the unique signal path of at least some unknown impedance (as shown in equations 2-6 below) uses the peak voltage measured in the calibration measurement as a numerical constant.

Resistors having known resistance values may be provided on-chip with the circuit 150 or off-chip (as shown). The calibration measurement is optional if the peak voltage of the signal generator is known. The calibration measurement may only need to be performed once and need not be performed each time an impedance measurement is taken.

In the example shown, for calibration measurements, an (off-chip) resistor R _CAL having a known stable resistance value is coupled between pins RCAL1 and RCAL 2. the multiplexer 112 is configured to couple the signal path from pin RCAL1 to the signal generator 116 and to couple the signal path from pin RCAL2 to the current measurement circuit 126. the multiplexer 112 forms a signal path from the output of the signal generator 116 to the input of the current measurement circuit 126, and the signal path includes a resistor R _CAL. the multiplexer 112 connects the output of the signal generator 116 to the input of the current measurement circuit 126 through resistor R _CAL. the measured current performed by the current measurement circuit is I _CAL. with the known resistance value of resistor R _CAL, the voltage V _CAL across resistor R _CAL ═ I _CAL · R _CAL can be derived, the measured current I _CAL and the known resistance value of resistor R _CAL form equation 1, as shown below.

_{E1 E2 E3 E4}5-9 show five current measurements, which establish a system of five equations from which five unknown impedances (bioimpedance and four contact impedances) can be derived from solving the system of five equations.

In FIG. 5, multiplexer 112 is configured to couple the signal path from pin CE0 to the output of signal generator 116 and to couple the signal path from pin AIN1 to the input of current measurement circuit 126. The measured current obtained by the current measurement circuit 126 is I₁. Measured current I₁Measured current I_CALAnd R_CALThe known resistance value of (a) forms equation 2, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path comprises an unknown contact impedance Z_E1Unknown bio-impedance Z_{Machine body}And an unknown contact impedance Z_E4(in series). The signal path includes a branch with electrode 104 and pin CE0, and a branch with electrode 110 and pin AIN 1. Equation 2 encapsulates the three unknown impedances Z in the signal path_E1、Z_{Machine body}And Z_E4And measuring the current I₁Measuring the current I_CALAnd R_CALKnown resistance values. Note that the measured current I_CALAnd R_CALIs equal to the voltage V obtained from the calibration measurement_CAL。

in FIG. 6, the multiplexer 112 is configured to couple a signal path from pin CE0 to the output of the signal generator 116 and a signal path from pin AIN2 to the input of the current measurement circuit 126. the measured current obtained by the current measurement circuit 126 is I ₂. the measured current I ₂, the measured currents I _CAL and the known resistance values of R _CAL form equation 3, as shown below. the multiplexer 112 forms a signal path from the signal generator 116 to the current measurement circuit 126. the signal path includes an unknown contact impedance Z _E1 and an unknown contact impedance Z _E2 (in series). the signal path includes a branch having an electrode 104 and pin CE0, and a branch having an electrode 106 and pin AIN 2. equation 3 encapsulates the relationship between the two unknown impedances Z _E1 and Z _E2 in the signal path and the known resistance values of the measured currents I ₂, I _CAL and R _CAL.

In fig. 7, multiplexer 112 is configured to couple the signal path from pin CE0 to the output of signal generator 116 and to couple the signal path from pin AIN3 to the input of current measurement circuit 126. Through current measuring circuit126 is obtained a measured current of I₃. Measured current I₃Measured current I_CALAnd R_CALThe known resistance value of (a) forms equation 4, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path comprises an unknown contact impedance Z_E1Unknown bio-impedance Z_{Machine body}And an unknown contact impedance Z_E3(in series). The signal path includes a branch with electrode 104 and pin CE0, and a branch with electrode 108 and pin AIN 3. Equation 4 encapsulates the three unknown impedances Z in the signal path_E1、Z_{Machine body}And Z_E3With measured current I₃Measured current I_CALAnd R_CALKnown resistance values.

In fig. 8, multiplexer 112 is configured to couple the signal path from pin AIN2 to the output of signal generator 116 and to couple the signal path from pin AIN1 to the input of current measurement circuit 126. The measured current obtained by the current measuring circuit 126 is I₄. Measured current I₄Measured current I_CALAnd R_CALThe known resistance value of (a) forms equation 5, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path comprises an unknown contact impedance Z_E2Unknown bio-impedance Z_{Machine body}And an unknown contact impedance Z_E4(in series). The signal path includes a branch with electrode 106 and pin AIN2, and a branch with electrode 110 and pin AIN 1. Equation 5 encapsulates the three unknown impedances Z in the signal path_E2、Z_{Machine body}And Z_E4With measured current I₄Measured current I_CALAnd R_CALKnown resistance values.

In FIG. 9, the multiplexer 112 is configured to couple the signal path from pin AIN3 to the output of the signal generator 116 and to couple the signal path from pin AIN1 to the input of the current measurement circuit 126. the measured current obtained by the current measurement circuit 126 is I ₅. the measured current I ₅, the measured currents I _CAL and the known resistance values of R _CAL form equation 6, as shown below. the multiplexer 112 forms a signal path from the signal generator 116 to the current measurement circuit 126. the signal path includes an unknown contact impedance Z _E3 and an unknown contact impedance Z _E4 (in series). the signal path includes a branch having an electrode 108 and pin AIN3, and a branch having an electrode 110 and pin AIN 1. equation 6 encapsulates the relationship between the two unknown impedances Z _E3 and Z _E4 in the signal path and the known resistance values of the measured currents I ₅, I _CAL and R _CAL.

Using five equations (Eq.2-6) and five unknown impedances Z_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4five unknown impedances Z can be derived and determined_{machine body}、Z_E1、Z_E2、Z_E3and Z_E4The value of (c). As shown in fig. 5-9, each unique signal path includes two branch impedances. Also, as shown in fig. 5, 7 and 8, each of some of the unique signal paths may include a bioimpedance and two branch impedances. Each unique signal path includes at least some unknown impedance, and the unique signal paths together include each unknown impedance at least once.

The five equations (Eq. 2-6) can be rewritten as Eq. 7-11 based on one or more current measurements (I)₁、I₂、I₃、I₄And I₅One or more of), the measured current I_CALAnd the known resistance value of RCAL gives the unknown impedance Z_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4. Digital circuitry 190, such as a microcontroller or microprocessor, may be implemented to base the measurements seen in FIGS. 4-9 and equations 7-11 onThe unknown impedance is calculated. The computer readable memory 192 may store the measurements, as well as instructions for processing the measurements to derive the impedance.

The measurements shown in fig. 4-9 may be performed in any order. In some cases, more than five measurements may be made to generate more than five equations.

The arrangement shown in fig. 4-9 may have several advantages. Note that it is no longer necessary to cross the unknown bioimpedance Z_{Machine body}voltage measurement (which is typically required in the four-wire impedance measurement shown in fig. 1). As a result, the expensive inAmp120 is no longer required in the circuit 150. In addition, the ground capacitance induced errors of pins AIN2 and AIN3 (acting as low pass filters), which result in V_AVoltage and V of_CIn a different way, V_BVoltage and V of_DVoltage difference) is no longer relevant because no voltage measurement is made. In addition, the scheme can effectively derive five impedances Z_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4。

Another exemplary scheme for deriving contact impedance through multiple measurements and signal processing

In the previous scheme shown by the measurements shown in fig. 4-9, there is a limit: the current leaks. Fig. 10 illustrates the current leakage present in the measurement seen in fig. 5, according to some embodiments of the present disclosure. When current measurement is carried out, e.g. current I₁(as shown in fig. 5), the branches not connected to the signal generator 116 or the current measurement circuit 126 ideally have infinite impedance. With infinite impedance, a branch not connected to the signal generator 116 or the current measurement circuit 126 will have zero current. In other words, I_ZE2(Current through a Branch having electrode 106 and pin Ain 2) and I_ZE3The current (through the branch having electrode 108 and pin AIN 3) is ideally zero. As a result, I_ZE1Will be equal to I_{Machine body}(Current through unknown bioimpedance) and is also equal to I_TIA(general)Current flowing through the branch). This would mean that no current is leaking through the branch with electrodes 106 and 108, and that the current measurement circuit 126 is accurately measuring through the unknown bioimpedance Z_{Machine body}Current (I) of_TIA＝I_{Machine body}). In practice, the branches not connected to the signal generator 116 or the current measurement circuit 126 do not have infinite impedance and may have grounded capacitances 1002 and 1004 (e.g., in the pF or μ F range). The grounded capacitances 1002 and 1004 represent circuitry capable of sinking current in the branches (e.g., circuitry in the multiplexer 112). As a result, the current I_ZE1May flow through a branch that is not connected to the signal generator 116 or the current measurement circuit 126. This means that I_ZE2And I_ZE3Is not zero, and I_ZE1May not be equal to I_{machine body}And may not be equal to I_TIA. As a result, current leaks through the branch having electrodes 106 and 108, and current measurement circuit 126 is inaccurately measuring the impedance Z through the unknown bioimpedance_{Machine body}Current (I) of_TIA≠I_{Machine body})。

To address this limitation, the current measurements that establish the system of equations with unknown impedance may be modified. In particular, the configuration of the multiplexer 112 is adapted for each measurement, and a different system of equations is used to derive the unknown impedance. Rather than having some signal paths floating, all signal paths are connected to the signal generator 116 or the current measurement circuit 126. Rather than each comprising only a subset of the unknown impedances or only two of the four branches, the unique signal path or unique impedance network would comprise all of the bio-impedances and branch impedances, and all four branches. As a result, the leakage current can be captured by the system of equations.

For four current measurements, one signal path is connected to the signal generator 116 and the other three signal paths are connected to the current measurement circuit 126. One of the four branches is connected to the output of the signal generator 116 and the other three of the four branches are connected to the input of the current measurement circuit 126. For another current measurement, two signal paths are connected to the signal generator 116 and two other signal paths are connected to the current measurement circuit 126. Two of the four branches are connected to the output of the signal generator 116 and the other two of the four branches are connected to the input of the current measurement circuit 126. Thus, the absence of a floating branch will result in current leakage or sinking current. The five current measurements form a different set of equations because the entire signal path formed by the multiplexer 112 from the signal generator 116 to the current measurement circuit 126 now involves parallel impedances (i.e., parallel unknown impedances). However, a system of equations with five equations may still determine five unknown impedances.

By configuring the multiplexer 112 and making multiple current measurements, the unknown impedance of the system, including the unknown bioimpedance Z, can be derived based on the system of equations_{Machine body}And contact impedance Z_E1、Z_E2、Z_E3And Z_E4. The system of equations is formed by the calibration measurements and several current measurements of different, unique signal paths are formed by the configuration multiplexer 112. The multiplexer 112 may selectively couple the output of the signal generator 116 and the input of the current measurement circuit 126 to different pins (e.g., RCAL1, RCAL2, CE0, AIN2, AIN3, and AIN 1). Thus, the multiplexer 112 may connect the output of the signal generator 116 to the input of the current measurement circuit 126 through a different signal path or a different impedance network involving all unknown impedances. The different unique signal paths form unique impedance networks, each combining all the unknown impedances of the system: unknown bioimpedance Z_{Machine body}And contact impedance Z_E1、Z_E2、Z_E3And Z_E4And has unique topological structure. The unique signal paths or unique impedance networks, each involving all unknown impedances, and the current measurements of the unique signal paths or unique impedance networks, establish a system of equations for the unknown impedances. Effectively, the signal generator 116 may excite the unique signal path or unique impedance network formed by the multiplexer 112, and the current measurement circuit 126 may measure the current through the unique signal path or unique impedance network.

To determine five unknown impedances (bio-impedance and four contact impedances), at least five equations are required. With a sufficient number of equations, five unknown impedances can be derived by signal processing (i.e., calculation). By appropriate processing, the current measurement allows determination of the bio-impedance and the contact impedance. The current measurement may be performed by the current measurement circuit 126. The signal processing may be performed in the digital domain, for example, by digital circuitry 190. Digital circuitry 190 may include dedicated digital hardware to perform signal processing. Digital circuitry 190 may include a microprocessor or microcontroller configured to execute instructions that implement signal processing. Digital circuitry 190 may be provided on-chip with circuitry 150 or off-chip (as shown). Digital circuit 190 may be implemented to control multiplexer 112 to form a unique signal path or a unique impedance network from signal generator 116 to current measurement circuit 126. The computer readable memory 192 may store the measured values. Computer readable memory 192 may store instructions that implement signal processing. Computer-readable memory 192 may be provided on-chip with circuitry 150 or off-chip (as shown).

In this modified version, calibration measurements may be performed based on the configuration seen in FIG. 4 and equation 1, which yields V _CAL FIGS. 11-15 show five current measurements according to embodiments of the present disclosure five current measurements create a system of five equations from which five unknown impedances (bioimpedance and four contact impedances) may be derived from solving the system of five equations.

in FIG. 11, the multiplexer 112 is configured to couple the signal path from pin CE0 to the output of the signal generator 116, couple the signal path from pin AIN2 to the input of the current measurement circuit 126, couple the signal path from pin AIN3 to the input of the current measurement circuit 126, couple the signal path from pin AIN1 to the current measurement circuit 126An input of the magnitude circuit 126. The measured current accomplished by the current measurement circuit 126 is I₁. The configuration of the multiplexer 112 in FIG. 11 is formed to include Z's in series_E1Overall signal path (parallel Z)_E2(Z in series)_{Machine body}) (ZE3 and ZE4 in parallel)). The branch with electrode 104 and pin CE0 is connected to the output of signal generator 116. The branch having electrode 106 and pin AIN2 is connected to an input of current measurement circuit 126. The branch having electrode 108 and pin AIN3 is connected to an input of current measurement circuit 126. The branch having electrode 110 and pin AIN1 is connected to an input of current measurement circuit 126. Measured current I₁Measuring the voltage V_CALEquation 12 is formed, as follows. Equation 12 encapsulates the measured current I₁Measuring voltage V_CALAnd the unknown impedance in the entire signal path from the signal generator 116 to the current measurement circuit 126 (formed by the multiplexer 112 in the configuration shown in fig. 11).

In fig. 12, the multiplexer 112 is configured to couple the signal path from pin AIN2 to the output of the signal generator 116, to couple the signal path from pin CE0 to the input of the current measurement circuit 126, to couple the signal path from pin AIN3 to the input of the current measurement circuit 126, and to couple the signal path from pin AIN1 to the input of the current measurement circuit 126. The measured current accomplished by the current measurement circuit 126 is I₂. The configuration of the multiplexer 112 in FIG. 12 is formed to include Z's in series_E2Overall signal path (parallel Z)_E1(Z in series)_{Machine body})(Z_E3And Z_E4In parallel)). The branch having electrode 104 and pin CE0 is connected to an input of current measurement circuit 126. A branch having an electrode 106 and pin AIN2 is connected to the output of signal generator 116. The branch having electrode 108 and pin AIN3 is connected to an input of current measurement circuit 126. The branch having electrode 110 and pin AIN1 is connected to an input of current measurement circuit 126. Measured current I₂Measuring the voltage V_CALequation 13 is formed, as follows. Equation 13 encapsulates the measured current I₂Measuring voltage V_CALFrom the signal generator 116 to the current measurement circuit 126 (shown in FIG. 12 byThe multiplexer 112 in the configuration) of the signal path.

In fig. 13, the multiplexer 112 is configured to couple the signal path from pin AIN3 to the output of the signal generator 116, to couple the signal path from pin CE0 to the input of the current measurement circuit 126, to couple the signal path from pin AIN2 to the input of the current measurement circuit 126, and to couple the signal path from pin AIN1 to the input of the current measurement circuit 126. The measured current accomplished by the current measurement circuit 126 is I₃. The configuration of the multiplexer 112 in FIG. 13 is formed to include Z's in series_E3Overall signal path (parallel Z)_E4(Z in series)_{Machine body})(Z_E1And Z_E2In parallel)). The branch having electrode 104 and pin CE0 is connected to an input of current measurement circuit 126. The branch having electrode 106 and pin AIN2 is connected to an input of current measurement circuit 126. A branch having an electrode 108 and pin AIN3 is connected to the output of signal generator 116. The branch having electrode 110 and pin AIN1 is connected to an input of current measurement circuit 126. Measuring current I₃Measuring the voltage V_CALEquation 14 is formed, as follows. Equation 14 encapsulates the measured current I₃Measuring voltage V_CALAnd unknown impedance in the entire signal path from the signal generator 116 to the current measurement circuit 126 (formed by the multiplexer 112 in the configuration shown in fig. 13).

in fig. 14, multiplexer 112 is configured to couple a signal path from pin AIN1 to signal generator 116, a signal path from pin CE0 to current measurement circuitry 126, a signal path from pin AIN2 to current measurement circuitry 126, and a signal path from pin AIN3 to current measurement circuitry 126. The measured current accomplished by the current measurement circuit 126 is I₄. The configuration of the multiplexer 112 in FIG. 14 is formed to include Z's in series_E4Overall signal path (parallel Z)_E3(Z in series)_{Machine body})(Z_E1And Z_E2In parallel)). The branch having electrode 104 and pin CE0 is connected to an input of current measurement circuit 126. The branch with electrode 106 and pin AIN2 is connected to a current measurementThe input of circuit 126. The branch having electrode 108 and pin AIN3 is connected to an input of current measurement circuit 126. A branch having an electrode 110 and pin AIN1 is connected to the output of signal generator 116. Measuring current I₄Measuring the voltage V_CALEquation 15 is formed, as follows. Equation 15 encapsulates the measured current I₄Measuring voltage V_CAL and the unknown impedance in the entire signal path from the signal generator 116 to the current measurement circuit 126 (formed by the multiplexer 112 in the configuration shown in fig. 14).

In fig. 15, the multiplexer 112 is configured to couple the signal path from the pin CE0 to the signal generator 116, to couple the signal path from the pin AIN2 to the signal generator 116 (and, to couple the signal path from the pin AIN3 to the current measurement circuit 126, and to couple the signal path from the pin AIN1 to the current measurement circuit 126. The measured current accomplished by the current measurement circuit 126 is I₅. The configuration of multiplexer 112 in FIG. 15 forms an integral signal path that includes (Z)_E1And Z_E2In parallel) with Z_{Machine body}In series and with (Z)_E3And Z_E4Parallel) in series. The branch having electrode 104 and pin CE0 is connected to the output of signal generator 116. A branch having an electrode 106 and pin AIN2 is connected to the output of signal generator 116. The branch having electrode 108 and pin AIN3 is connected to an input of current measurement circuit 126. The branch with electrode 110 and pin AIN1 is connected to an input of current measurement circuit 126. Measured current I₅Measuring the voltage V_CALEquation 16 is formed, as follows. Equation 16 encapsulates the measured current I₅Measuring voltage V_CALAnd the unknown impedance in the entire signal path from the signal generator 116 to the current measurement circuit 126 (formed by the multiplexer 112 in the configuration shown in fig. 15).

An alternative to the signal path shown in fig. 15 is to connect the branch with electrode 104 and pin CE0, and the branch with electrode 106 and pin AIN2 to the input of current measurement circuit 126, and the branch with electrode 108 and pin AIN3 and the branch with electrode 110 and pin AIN1 to the output of signal generator 116.

Equations 17-21 show equations 12-16 in an expanded form based on the sign of the parallel impedances.

Using five equations (Eq. 12-16) and five unknown impedances Z_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4Five unknown impedances Z can be derived and determined_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4The value of (c). As shown in fig. 11-15, each unique signal path includes all unknown impedances. Also, as shown in fig. 5, 7 and 8, each of some of the unique signal paths may include a bioimpedance and two branch impedances. Each unique signal path includes at least some unknown impedance, and the unique signal paths together include each unknown impedance at least once.

Algebraic operations may be applied to equations 17-21 to rewrite equations 12-21 such that the impedance Z is unknown_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4Based on current measurements (e.g. I)₁、I₂、I₃、I₄And I and₅) The measured current I_CALAnd R_CALIs defined as the known resistance value. The following pseudo code may be implemented in digital circuitry 190, such as a microcontroller or microprocessor, to determine and calculate the unknown impedance based on the measurements seen in fig. 4 and 11-15.

The measurements seen in fig. 4 and 11-15 may be performed in any order. In some cases, more than five measurements may be made to generate more than five equations.

The arrangements shown in fig. 4 and 11-15 may have several advantages (similar to the arrangements shown in fig. 4-9). Note that it is no longer necessary to cross the unknown bioimpedance Z_{Machine body}Voltage measurement (which is typically required in the four-wire impedance measurement shown in fig. 1). As a result, the expensive inAmp120 is no longer required in the circuit 150. Furthermore, since no voltage measurement is made, errors due to the grounded capacitance of pins AIN2 and AIN3 (which act as low pass filters) (which result in V)_AVoltage and V of_CDifferent from each other, V_BVoltage and V of_DDifferent) are no longer relevant. In addition, the scheme can effectively and accurately derive five impedances Z_{Machine body}、Z_E1、Z_E2、Z_E3And Z_E4. In addition to these advantages, this solution can now ensure accuracy even in the presence of a large imbalance between high impedance and contact impedance.

Other technical advantages

Measuring bio-impedance is particularly useful for measuring body impedance for detecting fluid levels in the lungs or measuring thoracic impedance. Measuring bioimpedance may also be used in electrical impedance tomography to non-invasively determine the composition of a body (e.g., imaging of tissues and bones) by making bioimpedance measurements at different frequencies. Measuring bio-impedance can be used to measure respiratory activity, which can be obtained by observing changes in thoracic impedance. Measuring the bio-impedance and the contact impedance means that breathing activity can be obtained even in the presence of motion, since changes in the contact impedance can be taken into account. Users such as athletes and patients may benefit from these applications.

Except for unknown bio-impedance Z_{machine body}In addition, the contact impedance Z is known_E1、Z_E2、Z_E3And Z_E4The circuitry may be enabled to infer whether the contact (i.e., the contact formed by the electrodes contacting the body) is good, for example, as part of a diagnostic process. For example, a high contact impedance may indicate that the patch/electrode is not properly attached to the body. Thus, information about the quality of the contact can be inferred from the derived contact impedance.

For example, digital circuitry 190 may determine the quality of the contacts corresponding to the four electrodes based on the impedances of the four branches. If the given impedance of the branch is too high, the digital circuit 190 may infer that the contact of the branch is bad and output a signal indicating that there is a bad contact and optionally output an identifier identifying which contact is bad. The digital circuit 190 may compare the impedances of the four branches to predetermined thresholds to determine whether a given impedance is too high.

User feedback may be provided based on inferred information about contact quality. In another example, smart drug delivery applications may require proper contact with the body to ensure proper and effective drug delivery. If not properly contacted, the drug may accumulate on the skin due to malabsorption and skin contact. Other applications, such as electrocardiography or defibrillation, may also require proper contact with the body. Being able to infer the quality of the contact based on the derived contact impedance may provide feedback to the user regarding the quality of the contact in such a context.

Some efforts to extract contact quality or contact impedance have limitations, and the approaches described herein for measuring impedance may improve these efforts. In some systems, efforts to extract contact quality or contact impedance ignore or assume that the bio-impedance is zero, near zero, or very small compared to the contact impedance. This assumption is reasonable when the electrodes measure the electrical activity of the heart, because in this case the electrodes are placed close to each other (e.g. on the chest) and the skin is already prepared so that the body impedance is very small. The impedance measurement scheme described herein does not make such an assumption. In situations where the body impedance may be large, it may be beneficial to not make this assumption. For example, when the electrodes are placed on other parts of the body that are far from each other, the body impedance cannot be neglected, wherein the bio-impedance may be in the range of the contact impedance. In another example, if the electrodes have a very low impedance, the bio-impedance may be much greater than the contact impedance. In another example, the lack of skin preparation may also cause the contact impedance to be much greater than the measured bio-impedance. For all of these reasons, the impedance measurement scheme described herein may be used in a variety of situations. For example, impedance measurement schemes may be used to non-invasively obtain a composition of a body, determine thoracic impedance, determine respiratory activity in the case of exercise, and the like.

Method for measuring impedance

Fig. 16 is a flow chart illustrating a method for measuring impedance according to some embodiments of the present disclosure. The impedances include a bioimpedance and four branch impedances. In 1602, a circuit, such as multiplexer 112, may form a unique signal path. At 1604, the current measurement circuit 126 may make current measurements of the unique signal paths. The unique signal paths establish a system of equations from which the impedance can be derived. To ensure that the system of equations will produce unknown impedances, each unique signal path includes at least some of the impedances, and the unique signal path includes each impedance at least once. In 1606, digital circuit 190 can derive an impedance based on the current measurement.

Examples of the present invention

Example 1 is a method of measuring impedance, comprising: forming unique signal paths, wherein each unique signal path includes at least some of the impedances, the unique signal paths include at least once per impedance, and the impedances include a bioimpedance and four branch impedances, taking a current measurement of the unique signal paths, and deriving the impedances based on the current measurements.

In example 2, the method of example 1 may optionally comprise: deriving a voltage from the signal generator by applying the output of the signal generator to a resistor of known resistance and measuring the current through the resistor, and deriving the impedance further based on the voltage from the signal generator.

In example 3, the method of example 1 or 2 may optionally comprise: forming the signal path includes: a configurable network is controlled to connect an output of the signal generator to the unique signal path and to connect an input of a current measurement circuit to the unique signal path.

In example 4, the method of any one of examples 1-3 can optionally include: performing a current measurement comprises: a signal from a signal generator is applied to the unique signal paths, and the current through each unique signal path is measured by a current measurement circuit.

In example 5, the method of any one of examples 1-4 may optionally include: each distinct signal path includes two branch impedances.

In example 6, the method of any one of examples 1-5 can optionally include: each of some of the unique signal paths includes a bio-impedance and two branch impedances.

In example 7, the method of any one of examples 1-6 can optionally include: each unique signal path includes a network of all impedances.

example 8 is a circuit to measure impedance, comprising: a signal generator for generating a signal at an output of the signal generator, a current measurement circuit for measuring a current at an input of the current measurement circuit, a configurable network for connecting the output of the signal generator to the input of the current measurement circuit via unique signal paths, wherein each unique signal path comprises at least some of: a bioimpedance and a branch impedance, and a digital circuit to determine the bioimpedance and the branch impedance based on a current measurement of the unique signal path.

In example 9, the circuitry of example 8 may optionally include: the configurable network connects the output of the signal generator to the input of the current measurement circuit via at least five distinct signal paths, and the current measurement circuit measures at least five current measurements.

In example 10, the circuit of examples 8 or 9 may optionally include: digital circuitry determines the bio-impedance and four branch impedances based on at least five current measurements of the unique signal path.

In example 11, the circuit of any one of examples 8-10 may optionally include: the unique signal path includes each of the bioimpedance and the branch impedance at least once.

In example 12, the circuitry of any one of examples 8-11 may optionally include: each distinct signal path includes two branch impedances.

In example 13, the circuit of any one of examples 8-12 may optionally include: each of some of the unique signal paths includes a bio-impedance and two branch impedances.

in example 14, the circuit of any one of examples 8-13 may optionally include: each unique signal path includes a network of all bio-impedances and branch impedances.

In example 15, the circuit of any one of examples 8-14 may optionally include: the configurable network further connects an output of the signal generator to an input of the current measurement circuit through a resistor having a known resistance value, and the current measurement circuit further measures the current through the resistor to determine the voltage from the signal generator.

Example 16 is a circuit to measure impedance, comprising: four branches each having four electrodes, wherein two of the four electrodes are connected to a first end of a bioimpedance and the other two of the four electrodes are connected to a second end of the bioimpedance, circuitry to apply signals to at least five unique impedance networks and to make current measurements of the at least five unique impedance networks, wherein each unique impedance network has at least two of the four branches, digital circuitry to derive the bioimpedance and the impedances of the four branches based on the current measurements.

In example 17, the circuitry of example 16 may optionally include: each unique impedance network includes all four branches.

In example 18, the circuit of example 16 or 17 may optionally include: the at least five unique impedance networks include such unique impedance networks: with one of the four branches connected to the signal generator and the other three of the four branches connected to the current measuring circuit.

In example 19, the circuitry of any of examples 16-18 may optionally include: the at least five distinct impedance networks include a second distinct impedance network: with two of the four branches connected to the signal generator and the other two of the four branches connected to the current measuring circuit.

In example 20, the circuitry of any of examples 16-19 may optionally include: the circuit is operable to further connect the output of the signal generator to the input of the current measuring circuit through a resistor having a known resistance value and to further measure the current through the resistor to determine a measured voltage from the signal generator.

In example 21, the circuit of any one of examples 16-20 may optionally include: digital circuitry determines contact qualities corresponding to the four electrodes based on the impedances of the four branches.

In example 22, the circuitry of any of examples 16-21 may optionally include: the unique impedance network includes at least once a bioimpedance and each of the four branched impedances.

In example 23, the circuitry of any of examples 16-22 may optionally include: each of some of the unique impedance networks includes a bioimpedance and an impedance of two of the four branches.

In example 24, the circuit of any one of examples 16-23 may optionally include: each unique impedance network includes a network of all bio-impedances and impedances of four branches.

Variations and implementations

The unique signal paths shown in this disclosure are not meant to be limiting. Other topologies, schemes for exciting and measuring signal paths may be implemented and are contemplated by the present disclosure.

Furthermore, certain embodiments discussed above may be provided in digital signal processing techniques for medical imaging, patient monitoring, medical instrumentation, and home healthcare. Embodiments herein may also be beneficial for other applications that require accurate impedance measurements using at least four electrodes.

In the discussion of the above embodiments, the various electrical components may be readily replaced, or otherwise modified to accommodate particular circuit requirements. Further, it should be noted that the use of complementary electronics, hardware, software, etc. provides an equally viable option for implementing the teachings of the present disclosure.

The portions of the various circuits used to derive the unknown impedance may include electronic circuits that perform the functions described herein. In some cases, one or more portions of circuitry may be provided by a processor specifically configured to perform the functions described herein. For example, a processor may include one or more special-purpose components, or may include programmable logic gates configured to perform the functions described herein. The circuit may operate in the analog domain, the digital domain, or the mixed signal domain. In some cases, a processor may be configured to perform the functions described herein by executing one or more instructions stored on a non-transitory computer medium. In some embodiments, an apparatus may comprise means for performing or carrying out one or more of the functions described herein.

It must also be noted that all specifications, dimensions, and relationships (e.g., number of processors, logical operations, etc.) summarized herein are provided for purposes of example and teaching only. Such information may be varied significantly without departing from the spirit of the present disclosure. The specifications apply only to one non-limiting example, and therefore they should be interpreted as such. In the foregoing description, examples have been described with reference to particular processors and/or component arrangements. Various modifications and changes may be made to such embodiments without departing from the scope of the present disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Note that with the numerous examples provided herein, interaction may be described in terms of two, three, four, or more electronic components. However, this is for clarity and illustration only. It should be appreciated that the systems may be combined in any suitable manner. Along similar design alternatives, any of the illustrated components, modules, and elements in the figures may be combined in various possible configurations, all of which are clearly within the broad scope of this specification. In some cases, it may be easier to describe one or more functions of a given flow set by only referencing a limited number of electrical elements. It will be appreciated that the circuitry of the figures and their teachings is readily scalable and can accommodate a large number of components, as well as more complex/sophisticated arrangements and configurations. Accordingly, the examples provided should not limit the scope or inhibit the broad teachings of the circuitry that may be applied to myriad other architectures.

Note that in this specification, references to various features (e.g., elements, structures, modules, components, steps, operations, characteristics, etc.) included in "one embodiment", "an example embodiment", "an embodiment", "another embodiment", "some embodiments", "various embodiments", "other embodiments", "alternative embodiments", etc., are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not be combined in the same embodiments.

It is also important to note that the functions related to deriving unknown impedance are merely illustrative of some of the possible functions that may be performed by or within the system shown in the figures. Some of these operations may be deleted or removed where appropriate, or these operations may be significantly modified or changed without departing from the scope of the present disclosure. In addition, the time of these operations may vary greatly. The preceding operational flows are provided for purposes of example and discussion. The embodiments described herein provide substantial flexibility in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings of the present disclosure.