Bioimpedance and contact impedance measurements

Abstract

This disclosure relates to the measurement of bioimpedance and contact impedance. Accurate measurement of bioimpedance is important for sensing the characteristics of an organism. Unfortunately, contact impedance significantly reduces the accuracy of bioimpedance measurements. To address this problem, circuitry for implementing four-wire impedance measurements can be configured to perform multiple current measurements. These multiple current measurements establish a system of equations that allow the derivation of unknown bioimpedance and contact impedance. The result is accurate bioimpedance measurement unaffected by large contact impedance. Furthermore, poor contacts with undesirable high impedance can be identified.

Description

[0001] This application is a divisional application of the invention patent application filed on May 31, 2019, with application number 201910465785.2 and invention title "Bioimpedance and Contact Impedance Measurement".

[0002] Priority application

[0003] This patent application claims priority to and accepts the benefit of U.S. Provisional Application Serial No. 62 / 678,986, entitled "Measurement of Bioimpedance and Contact Impedance", filed May 31, 2018, and U.S. Provisional Application Serial No. 62 / 679,460, entitled "Measurement of Bioimpedance and Contact Impedance", filed June 1, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This invention relates to the field of integrated circuits, and more particularly to impedance measurement. Background Technology

[0005] Impedance measurement of the body, referred to herein as bioimpedance, has numerous applications in healthcare and consumer settings. Impedance measurements can be performed using electrodes provided in body-wear systems or wearable devices such as watches, chest straps, headbands, patches, etc. The circuitry coupled to the electrodes derives the unknown impedance of the body on which they are placed. Impedance measurement is particularly useful for monitoring vital signs, sensing tissue and fluid levels in the body, detecting signs of pulmonary edema, or assessing body composition. Furthermore, electrical impedance tomography (EIT) is an emerging non-invasive medical imaging technique. However, accurate bioimpedance measurements are not without challenges. Attached Figure Description

[0006] To gain a more complete understanding of this disclosure and its features and advantages, reference is made to the following description in conjunction with the accompanying drawings, wherein like reference numerals denote like parts, wherein:

[0007] Figure 1 The present disclosure illustrates a system having electrodes and circuitry according to some embodiments thereof, providing an exemplary manner for performing a four-wire impedance measurement of bioimpedance fabrication.

[0008] Figure 2 The input capacitance present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of the present disclosure is shown;

[0009] Figure 3 The current leakage present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of the present disclosure is shown;

[0010] Figure 4 Calibration measurements according to some embodiments of this disclosure are shown;

[0011] Figure 5-9 Five current measurements according to embodiments of the present disclosure are shown;

[0012] Figure 10 Some embodiments according to this disclosure are shown in Figure 5 Current leakage was observed in the measurements.

[0013] Figure 11-15 Five current measurements for avoiding current leakage according to embodiments of the present disclosure are shown; and

[0014] Figure 16 This is a flowchart illustrating a method for measuring impedance according to some embodiments of the present disclosure. Detailed Implementation

[0015] Overview

[0016] Accurate measurement of bioimpedance is crucial for sensing the characteristics of a host organism. Unfortunately, contact impedance significantly reduces the accuracy of bioimpedance measurements. To address this issue, circuitry can be configured to perform multiple current measurements to achieve four-wire impedance measurement. These multiple current measurements establish a system of equations that allow the derivation of unknown bioimpedance and contact impedance. The result is accurate bioimpedance measurement, unaffected by high contact impedance. Furthermore, poor contacts with undesirable high impedance can be identified.

[0017] Four-wire impedance measurement

[0018] One technique for impedance measurement is the four-terminal sensing scheme, or four-wire impedance measurement scheme. It is sometimes referred to as Kelvin sensing. This technique involves using four electrodes placed on the body to sense or derive unknown bioimpedance.

[0019] Figure 1 A system 100 according to some embodiments of the present disclosure is shown, having electrodes and circuitry in an exemplary manner for performing a four-wire impedance measurement to generate bioimpedance. In the figure, unknown bioimpedance is shown as Z. 机体 System 100 includes electrodes 104, 106, 108, and 110 (or contacts with the body). Electrodes 104, 106, 108, and 110 each have a contact resistance Z. E1 Z E2 Z E3 and Z E4 Contact resistance Z E1 Z E2 Z E3 and Z E4These can represent the skin electrode impedances of electrodes 104, 106, 108, and 110, respectively. The circuit 150, packaged as an integrated circuit or chip, has pins (or connections) that are connected 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.

[0020] 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 AIN1. Two branches are used to sense unknown bioimpedance Z. 机体 The first end, while the other two branches are used to sense the unknown bioimpedance Z. 机体 The second end. Including the branch of electrode 104 coupled to the unknown bioimpedance Z. 机体 The first end. Including the branch of electrode 106 coupled to the unknown bioimpedance Z. 机体 The first end. Including the branch of electrode 108 coupled to the unknown bioimpedance Z. 机体 The second end. Including the branch of electrode 110 coupled to the unknown bioimpedance Z. 机体 The second end. Four branches connect to corresponding pins of circuit 150. A portion of the branches outside circuit 150 can represent a cable with a patch at the cable end. A portion of the branches outside circuit 150 can also represent a conductor or wire with an electrode at the end of a conductor or wire. The conductor and electrode can be mounted in a wearable device. Optionally, C ISO1 C ISO2 C ISO3 C ISO4 The capacitors shown may be included between the pairs of electrodes and pins to provide isolation and protection (e.g., blocking DC signals) between the human user’s body and the circuitry within circuitry 150.

[0021] Circuit 150 may include a multiplexer (mux) 112. The mux 112 can be controlled in a manner that connects signal paths from different pins to different portions of circuit 150. As used herein, mux 112 represents a controllable, configurable network for connecting different portions of circuit 150 to different pins. For example, the multiplexer 112 can connect different portions of circuit 150 to different branches (branches with corresponding electrodes) connected to pins. Different configurations of the multiplexer 112 can form different signal paths or different impedance networks (impedance network is synonymous with signal path).

[0022] Circuit 150 may include a signal generator 116 (e.g., a sine wave generator). The signal generator can generate a peak voltage of V. 峰值The signal is generated at the output of the signal generator.

[0023] Circuit 150 may include voltage measurement circuit 118 to measure the voltage across its positive and negative input terminals. In some embodiments, voltage measurement circuit 118 may include an instrumentation amplifier (inAmp) 120 having positive and negative terminals for detecting the voltage difference between the positive and negative terminals and outputting a voltage output representing that voltage difference. Voltage measurement circuit 118 may include a Discrete Fourier Transform (DFT) block 122 and a summation block 124 to generate a voltage measurement based on the voltage output from 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.

[0024] Circuit 150 may further include current measurement circuit 126 to measure the current at its input. In some embodiments, current measurement circuit 126 may include a transimpedance amplifier (TIA) 128 to convert the current at the input terminal of TIA 128 into a voltage output representing the current. Current measurement circuit 126 may include a DFT block 130 and a summing block 132 to generate a current measurement based on the voltage output from 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.

[0025] To perform impedance measurements, a voltage is generated across the unknown bioimpedance, displayed as Z. 机体 Unknown bioimpedance Z 机体 The voltage on it can be considered as V A -V B Unknown bioimpedance Z 机体 The voltage on the signal generator 116 can be generated or applied. Simultaneously, the unknown bioimpedance Z... 机体 The voltage on the circuit is measured by voltage measurement circuit 118 and measured by unknown bioimpedance Z. 机体 The current can also be measured by the current measuring circuit 126. The measured voltage and current can be used to derive the unknown bioimpedance Z. 机体 The impedance value. Specifically, the unknown bioimpedance Z. 机体 The impedance value is related to the voltage measurement value divided by the current measurement value.

[0026] In traditional two-wire impedance measurements, a measurement problem may arise because the cable impedance (including contact impedance) is added to the unknown bioimpedance Z. 机体 This disrupts the impedance measurement. For simplicity, the existing impedances are pooled together as the contact impedance in each branch. Theoretically, four-wire impedance measurement can avoid this problem. When the unknown bioimpedance Z... 机体The measurement results can be sufficiently accurate when the impedance is much higher than that of the cable.

[0027] However, in practice, four-wire impedance measurements may have certain other limitations or non-ideals that can significantly affect the accuracy of bioimpedance measurements. For example, these limitations can be significant when impedance measurements are performed at low frequencies, high frequencies, certain frequencies, or a variety of frequencies. In some cases, the contact impedance Z... E1 Z E2 Z E3 and Z E4 One or more of them can be greater than the unknown bioimpedance Z. 机体 For example, mechanical and / or environmental factors (e.g., humidity, movement, hair on the skin, etc.) can cause poor contact and may significantly increase one or more contact resistances. In some severe cases, the contact resistance (amplitude) may exceed 2kΩ. In some cases, an optional capacitor C... ISO1 C ISO2 C ISO3 C ISO4 This can also significantly increase or affect the cable's impedance. In some cases, the contact impedance Z... E1 Z E2 Z E3 and Z E4 They can be unbalanced (e.g., the imbalance can be greater than 1 kΩ). These limitations have been found to reduce the accuracy of four-wire impedance measurements.

[0028] One of the problems that causes these limitations is the reduced accuracy of bioimpedance measurements, due to the potential presence of large input capacitances (e.g., approximately 40 pF) at pins AIN2 and AIN3. Figure 2 The diagram illustrates the input capacitance present in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of this disclosure. A ground input capacitor 202 may be present at pin AIN2, and a ground input capacitor 204 may be present at pin AIN3. Ground input capacitor 202, contact impedance Z E2 and capacitor C ISO2 A filter can be formed. This filter may be problematic because of the contact impedance Z. E2 Since the input capacitance is unknown, the filter's effectiveness is also unknown. The grounding input capacitor is 204, and the contact impedance is Z. E3 and capacitor C ISO3 This can also form another filter. This other filter might be problematic because of the contact impedance Z. E3 Since it is unknown, the effect of the other filters is also unknown. Ideally, the voltage V... A Should be related to voltage V C Same, voltage V B Should be related to voltage VD Same. Due to grounding input capacitors 202 and 204, at certain frequencies, the voltage V... A With voltage V C Different, and voltage V B With voltage V D Different. V A and V B The voltage across the terminals may be related to V. C and V D The voltages at the two ends are different. The negative effects of ground input capacitors 202 and 204 can be observed at low frequencies and when the contact impedance is high, for example, in the range of hundreds or thousands of ohms. Furthermore, ground input capacitors 202 and 204 can be attributed to an imbalance in contact impedance. An imbalance in the contact impedance of the branches can produce different cutoff frequencies, thus causing different attenuation in each branch.

[0029] Another problem that may reduce the accuracy of bioimpedance measurements is current leakage. Figure 3 The diagram illustrates current leakage in a circuit performing a four-wire impedance measurement of bioimpedance according to some embodiments of this disclosure. The current leakage occurs because the impedance Z of the branch with electrode 108... S- The impedance Z can be similar to that of a branch with electrode 110 driving TIA 128. F- This leads to the flow through the unknown bioresistance Z. 机体 Some current I 机体 The flow passes through the branch with electrode 108, and not all current I 机体 All currents will flow through the branch with electrode 110. In other words, the current I flowing through the branch with electrode 108... ZS- Ideally, it is zero, and the current I through the branch with electrode 110 is... ZF- Ideally equal to current I 机体 In fact, the current I ZS- It is not zero. As a result, the current I through the branch with electrode 110 is... ZF- Not equal to current I 机体 Furthermore, the current measuring circuit 126 does not measure the current I. 机体 As a result, current measurements are compromised, and consequently, impedance measurements are also compromised. The high contact impedance of the branch exacerbates this problem.

[0030] An exemplary scheme for deriving contact impedance through multiple measurements and signal processing.

[0031] By configuring the multiplexer 112 and performing multiple current measurements, the (unknown) impedance of the system, including the unknown bioimpedance Z, can be derived. 机体 and contact impedance Z E1 Z E2 ZE3 and Z E4 Based on a set of equations, the system of equations is formed through calibration measurements, and several other current measurements are formed by configuring multiplexer 112 to create different signal paths. Multiplexer 112 can selectively couple the output of signal generator 116 and the input of current measurement circuit 126 to different pins (e.g., RCAL1, RCAL2, CE0, AIN2, AIN3, and AIN1). Therefore, multiplexer 112 can connect the output of signal generator 116 to the input of current measurement circuit 126 via different signal paths or different impedance networks involving at least some unknown impedances. Different signal paths can individually include two or more unknown impedances of the system: unknown bioimpedance Z. 机体 and contact impedance Z E1 Z E2 Z E3 and Z E4 A set of equations for the unknown impedance is established by using at least some unique signal paths or unique impedance networks, and current measurements of these unique signal paths or unique impedance networks. Each unique signal path or unique impedance network includes at least one of the unknown impedances. Each unique signal path or unique impedance network will include at least some of the unknown impedances of the system. Effectively, signal generator 116 can excite the unique signal paths or unique impedance networks formed by multiplexer 112, and current measurement circuit 126 can measure the current passing through the unique signal paths or unique impedance networks.

[0032] To determine five unknown impedances (biological impedance and four contact impedances), at least five equations are required. Using a sufficient number of equations, the five unknown impedances can be derived through signal processing (i.e., computation). With appropriate processing, current measurement allows the determination of biological and contact impedances. Current measurement can be performed by current measurement circuitry 126. Signal processing can 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 to implement the signal processing. Digital circuitry 190 may be provided on-chip with circuitry 150 or off-chip (as shown). Digital circuitry 190 can be implemented to control multiplexer 112 to form a unique signal path or unique impedance network from signal generator 116 to current measurement circuitry 126. Computer-readable storage 192 can store the measured values. Computer-readable storage 192 can store instructions to implement the signal processing. Computer-readable storage 192 may be provided on-chip with circuitry 150 or off-chip (as shown).

[0033] Figure 4Calibration measurements according to some embodiments of this disclosure are illustrated. A calibration measurement is performed to determine the peak voltage from signal generator 116 (if it has not yet been measured or if it is not yet known). A set of equations (as shown in Equations 2-6 below) formed by current measurements through a unique signal path with at least some unknown impedance uses the peak voltage measured in the calibration measurement as a numerical constant. The unknown impedance is further derived based on the peak voltage measured in the calibration measurement. Determining the peak voltage from signal generator 116 can be performed in various ways. The output from signal generator 116 can be applied to a resistor with a known resistance value, and current measurement circuit 126 can measure the current through the resistor. The calibration measurement is represented by the following equation: V CAL =I CAL ·R CAL (Reproduce Equation 1 below). R CAL It is a resistor with a known stable resistance value. CAL The current is measured by the current measuring circuit 126. Therefore, the voltage V from the signal generator 116 can be derived. CAL .

[0034] A resistor with a known resistance value can be provided on-chip with circuit 150 or off-chip (as shown). If the peak voltage of the signal generator is known, calibration measurements are optional. Calibration measurements may only need to be performed once and do not need to be performed every time an impedance measurement is taken.

[0035] In the example shown, for calibration measurements, an off-chip resistor R has a known stable resistance value. CAL Coupled between pins RCAL1 and RCAL2. Multiplexer 112 is configured to couple a signal path from pin RCAL1 to signal generator 116 and a signal path from pin RCAL2 to current measurement circuit 126. Multiplexer 112 forms a signal path from the output of signal generator 116 to the input of current measurement circuit 126, and the signal path includes resistor R. CAL Multiplexer 112 is connected to resistor R. CAL The output of signal generator 116 is connected to the input of current measurement circuit 126. The measured current performed by the current measurement circuit is I. CAL Using resistor R CAL Given the known resistance value, the resistor R can be derived. CAL Voltage V across the terminals CAL =I CAL ·R CAL The measured current I CAL and resistor R CAL The known resistance value forms Equation 1, as shown below. Voltage V CALThis represents the (calibrated) peak voltage from signal generator 116. This is measured via R... CAL (that is, by including R) CAL The current in the signal path (via current measurement circuit 126) determines the current through R. CAL The measured value of voltage V CAL .

[0036] Figure 5-9 Five current measurements according to an embodiment of this disclosure are shown. The five current measurements establish a system of five equations, from which five unknown impedances (biological impedance and four contact impedances) can be derived by solving the system of five equations. Note that in each branch, for simplicity, the impedance in the cable connected to the pin and the contact impedance are grouped together and expressed as contact impedance (e.g., Z). E1 Z E2 Z E3 and Z E4 Therefore, the contact impedance represents the impedance of each branch.

[0037] exist Figure 5 In this circuit, multiplexer 112 is configured to couple a signal path from pin CE0 to the output of signal generator 116 and a signal path from pin AIN1 to the input of current measurement circuit 126. The measured current obtained by current measurement circuit 126 is I1. The measured current I1 and the measured current I... CAL and R CAL The known resistance values ​​form Equation 2, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path includes the unknown contact impedance Z. E1 Unknown bioimpedance Z 机体 and unknown contact impedance Z E4 (Series connection). The signal path includes a branch with electrode 104 and pin CE0, and a branch with electrode 110 and pin AIN1. Equation 2 encapsulates the three unknown impedances Z in the signal path. E1 Z 机体 and Z E4 With measuring current I1, measuring current I CAL and R CAL The relationship between known resistance values. Note the measured current I. CAL and R CAL The product of the known resistance values ​​is equal to the voltage V obtained from the calibration measurement. CAL .

[0038] exist Figure 6In this circuit, multiplexer 112 is configured to couple the signal path from pin CE0 to the output of signal generator 116 and the signal path from pin AIN2 to the input of current measurement circuit 126. The measured current obtained by current measurement circuit 126 is I2. The measured current I2 and the measured current I... CAL and R CAL The known resistance values ​​form Equation 3, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path includes the unknown contact impedance Z. E1 and unknown contact impedance Z E2 (Series connection). The signal path includes a branch with electrode 104 and pin CE0, and a branch with electrode 106 and pin AIN2. Equation 3 encapsulates the two unknown impedances Z in the signal path. E1 and Z E2 With measuring current I2, measuring current I CAL and R CAL The relationship between known resistance values.

[0039] exist Figure 7 In this circuit, multiplexer 112 is configured to couple a signal path from pin CE0 to the output of signal generator 116 and a signal path from pin AIN3 to the input of current measurement circuit 126. The measured current obtained by current measurement circuit 126 is I3. The measured current I3 and the measured current I... CAL and R CAL The known resistance values ​​form Equation 4, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path includes the unknown contact impedance Z. E1 Unknown bioimpedance Z 机体 and unknown contact impedance Z E3 (Series connection). The signal path includes a branch with electrode 104 and pin CE0, and a branch with electrode 108 and pin AIN3. Equation 4 encapsulates the three unknown impedances Z in the signal path. E1 Z 机体 and Z E3 With the measured current I3, the measured current I CAL and R CAL The relationship between known resistance values.

[0040] exist Figure 8 In this circuit, multiplexer 112 is configured to couple the signal path from pin AIN2 to the output of signal generator 116 and the signal path from pin AIN1 to the input of current measurement circuit 126. The measured current obtained by current measurement circuit 126 is I4. The measured current I4 and the measured current I...CAL and R CAL The known resistance values ​​form Equation 5, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path includes the unknown contact impedance Z. E2 Unknown bioimpedance Z 机体 and unknown contact impedance Z E4 (Series connection). The signal path includes a branch with electrode 106 and pin AIN2, and a branch with electrode 110 and pin AIN1. Equation 5 encapsulates the three unknown impedances Z in the signal path. E2 Z 机体 and Z E4 With the measured current I4, the measured current I CAL and R CAL The relationship between known resistance values.

[0041] exist Figure 9 In this circuit, multiplexer 112 is configured to couple a signal path from pin AIN3 to the output of signal generator 116 and a signal path from pin AIN1 to the input of current measurement circuit 126. The measured current obtained by current measurement circuit 126 is I5. The measured current I5 and the measured current I... CAL and R CAL The known resistance values ​​form Equation 6, as shown below. Multiplexer 112 forms a signal path from signal generator 116 to current measurement circuit 126. The signal path includes the unknown contact impedance Z. E3 and unknown contact impedance Z E4 (Series connection). The signal path includes a branch with electrode 108 and pin AIN3, and a branch with electrode 110 and pin AIN1. Equation 6 encapsulates the two unknown impedances Z in the signal path. E3 and Z E4 With measuring current I5, measuring current I CAL and R CAL The relationship between known resistance values.

[0042]

[0043]

[0044] Using five equations (Equation 2-6) and five unknown impedances Z 机体 Z E1 Z E2 Z E3 and Z E4 It can derive and determine five unknown impedances Z. 机体 Z E1 Z E2 ZE3 and Z E4 The value of . For example Figure 5-9 As shown, each unique signal path includes two branch impedances. Furthermore, as... Figure 5 , 7 As shown in Figure 8, each of the unique signal paths may include 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.

[0045] The five equations (Equations 2-6) can be rewritten as Equation 7-11, which is based on one or more current measurements (one or more of I1, I2, I3, I4, and I5) and the measured current I. CAL The known resistance value of RCAL gives the unknown impedance Z. 机体 Z E1 Z E2 Z E3 and Z E4 It can implement digital circuits 190, such as microcontrollers or microprocessors, to be based on Figure 4-9 The unknown impedance is calculated using the measurements seen in Equation 7-11. The computer-readable storage device 192 can store the measurement results, as well as instructions for processing the measurement results to derive the impedance.

[0046]

[0047]

[0048] Can be executed in any order Figure 4-9 The measurements shown are illustrated. In some cases, more than five measurements can be performed to generate more than five equations.

[0049] Figure 4-9 The proposed scheme has several advantages. Note that it no longer requires crossing the unknown bioimpedance Z. 机体 Voltage measurement (which is usually in) Figure 1 (Required in the four-wire impedance measurement shown). As a result, the expensive inAmp120 is no longer needed in circuit 150. Furthermore, the error caused by the ground capacitance of pins AIN2 and AIN3 (used as a low-pass filter) (which results in V...) A voltage and V C Different, V B voltage and V D The voltage difference is no longer relevant because no voltage measurement was performed. Furthermore, this scheme can effectively derive five impedances Z. 机体 Z E1 Z E2 Z E3 and Z E4 .

[0050] Another exemplary scheme for deriving contact impedance through multiple measurements and signal processing

[0051] exist Figure 4-9 The measurements shown in the previous scheme have a limitation: current leakage. Figure 10 Some embodiments according to this disclosure are shown in Figure 5 The measurement shows current leakage. When performing current measurements, such as current I1 (e.g.) Figure 5 As shown), the branch not connected to signal generator 116 or current measurement circuit 126 ideally has infinite impedance. With infinite impedance, the branch not connected to signal generator 116 or current measurement circuit 126 will have zero current. In other words, I... ZE2 (Current through the branch with electrode 106 and pin Ain2) and I ZE3 The current (through the branch with electrode 108 and pin AIN3) is ideally zero. As a result, I ZE1 Will equal I 机体 (Current passing through unknown biological impedance), and also equal to I TIA (Current through the branch). This means that no current leaks through the branch with electrodes 106 and 108, and the current measuring circuit 126 is accurately measuring the current through the unknown bioimpedance Z. 机体 The current (I) TIA =I 机体 In fact, branches not connected to signal generator 116 or current measurement circuit 126 do not have infinite impedance and can have ground capacitances 1002 and 1004 (e.g., in the range of pF or μF). Ground capacitances 1002 and 1004 represent circuits capable of absorbing current in the branches (e.g., circuits in multiplexer 112). As a result, current I ZE1 A portion can flow through a branch not connected to signal generator 116 or current measurement circuit 126. This means I ZE2 and I ZE3 Not zero, and I ZE1 It may not be equal to I 机体 And may not be equal to I TIA As a result, current leaks through the branch with electrodes 106 and 108, and the current measuring circuit 126 is inaccurately measuring the current through the unknown bioimpedance Z. 机体 The current (I) TIA ≠I 机体 ).

[0052] To overcome this limitation, the current measurement values ​​can be modified to establish a system of equations with unknown impedances. Specifically, the multiplexer 112 is configured for each measurement, and a different system of equations is used to derive the unknown impedance. Instead of leaving some signal paths floating, all signal paths are connected to the signal generator 116 or the current measurement circuit 126. A unique signal path or a unique impedance network, rather than each including only a subset of the unknown impedance or only two of the four branches, will include all the biological impedance and branch impedances, as well as all four branches. As a result, the leaked current can be captured by the system of equations.

[0053] For the four current measurements, one signal path connects to signal generator 116, and the other three signal paths connect to current measurement circuit 126. One of the four branches connects to the output of signal generator 116, and the other three branches connect to the input of current measurement circuit 126. For the other current measurement, two signal paths connect to signal generator 116, and the other two signal paths connect to current measurement circuit 126. Two of the four branches connect to the output of signal generator 116, and the other two branches connect to the input of current measurement circuit 126. Therefore, no floating branch would cause current leakage or current absorption. The five current measurements form different sets of equations because the entire signal path formed by multiplexer 112 from signal generator 116 to current measurement circuit 126 now involves parallel impedances (i.e., parallel unknown impedances). However, the set of five equations can still determine the five unknown impedances.

[0054] By configuring the multiplexer 112 and performing multiple current measurements, the unknown impedance of the system, including the unknown bioimpedance Z, can be derived based on the equation set. 机体 and contact resistance Z E1 Z E2 Z E3 and Z E4 A set of equations is formed through calibration measurements, and several current measurements are formed by configuring multiplexer 112 to create different, unique signal paths. Multiplexer 112 can selectively couple the output of signal generator 116 and the input of current measurement circuit 126 to different pins (e.g., RCAL1, RCAL2, CE0, AIN2, AIN3, and AIN1). Therefore, multiplexer 112 can connect the output of signal generator 116 to the input of current measurement circuit 126 via different signal paths or different impedance networks involving all unknown impedances. Different unique signal paths form unique impedance networks, each combining all unknown impedances of the system: unknown biological impedance Z. 机体 and contact impedance Z E1 ZE2 Z E3 and Z E4 It has a unique topology. A unique signal path or a unique impedance network, each involving all unknown impedances, and current measurement through the unique signal path or unique impedance network, establishes a set of equations for the unknown impedances. Effectively, the signal generator 116 can excite the unique signal path or unique impedance network formed by the multiplexer 112, and the current measurement circuit 126 can measure the current through the unique signal path or unique impedance network.

[0055] To determine five unknown impedances (biological impedance and four contact impedances), at least five equations are required. Using a sufficient number of equations, the five unknown impedances can be derived through signal processing (i.e., computation). With appropriate processing, current measurement allows the determination of biological and contact impedances. Current measurement can be performed by current measurement circuitry 126. Signal processing can 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 to implement the signal processing. Digital circuitry 190 may be provided on-chip with circuitry 150 or off-chip (as shown). Digital circuitry 190 can be implemented to control multiplexer 112 to form a unique signal path or unique impedance network from signal generator 116 to current measurement circuitry 126. Computer-readable storage 192 can store the measured values. Computer-readable storage 192 can store instructions to implement the signal processing. Computer-readable storage 192 may be provided on-chip with circuitry 150 or off-chip (as shown).

[0056] In this modified scheme, it can be based on Figure 4 The configuration seen in Equation 1 is used to perform calibration measurements, which produce V CAL . Figure 11-15 Five current measurements according to an embodiment of this disclosure are shown. The five current measurements establish a system of five equations, from which five unknown impedances (biological impedance and four contact impedances) can be derived by solving the system of five equations. Note that in each branch, for simplicity, the impedance in the cable connected to the pin is grouped together and expressed as contact impedance (e.g., Z). E1 Z E2 Z E3 and Z E4 Therefore, the contact impedance represents the impedance of each branch.

[0057] exist Figure 11In this circuit, multiplexer 112 is configured to couple a signal path from pin CE0 to the output of signal generator 116, a signal path from pin AIN2 to the input of current measurement circuit 126, a signal path from pin AIN3 to the input of current measurement circuit 126, and a signal path from pin AIN1 to the input of current measurement circuit 126. The current measured by current measurement circuit 126 is I1. Figure 11 The configuration of the multiplexer 112 in the middle forms a series of Z E1 The overall signal path (parallel Z) E2 (Z in series) 机体 (ZE3 and ZE4 are connected in parallel). The branch with electrode 104 and pin CE0 is connected to the output of signal generator 116. The branch with electrode 106 and pin AIN2 is connected to the input of current measurement circuit 126. The branch with electrode 108 and pin AIN3 is connected to the input of current measurement circuit 126. The branch with electrode 110 and pin AIN1 is connected to the input of current measurement circuit 126. The measured current I1 and the measured voltage V are... CAL This forms Equation 12, as shown below. Equation 12 encapsulates the measurement current I1 and the measurement voltage V. CAL From signal generator 116 to current measurement circuit 126 (by...) Figure 11 The relationship between the unknown impedances in the entire signal path (formed by the multiplexer 112 in the configuration shown).

[0058] exist Figure 12 In this circuit, multiplexer 112 is configured to couple a signal path from pin AIN2 to the output of signal generator 116, a signal path from pin CE0 to the input of current measurement circuit 126, a signal path from pin AIN3 to the input of current measurement circuit 126, and a signal path from pin AIN1 to the input of current measurement circuit 126. The current measured by current measurement circuit 126 is I2. Figure 12 The configuration of the multiplexer 112 in the middle forms a series of Z E2 The overall signal path (parallel Z) E1 (Z in series) 机体 (Z) E3 and Z E4 (Parallel connection). The branch with electrode 104 and pin CE0 is connected to the input of current measurement circuit 126. The branch with electrode 106 and pin AIN2 is connected to the output of signal generator 116. The branch with electrode 108 and pin AIN3 is connected to the input of current measurement circuit 126. The branch with electrode 110 and pin AIN1 is connected to the input of current measurement circuit 126. The measured current I2 and the measured voltage V are... CALThis forms Equation 13, as shown below. Equation 13 encapsulates the measurement of current I2 and voltage V. CAL From signal generator 116 to current measurement circuit 126 (by...) Figure 12 The relationship between the unknown impedances in the entire signal path formed by the multiplexer 112 in the configuration shown.

[0059] exist Figure 13 In this circuit, multiplexer 112 is configured to couple a signal path from pin AIN3 to the output of signal generator 116, a signal path from pin CE0 to the input of current measurement circuit 126, a signal path from pin AIN2 to the input of current measurement circuit 126, and a signal path from pin AIN1 to the input of current measurement circuit 126. The current measured by current measurement circuit 126 is I3. Figure 13 The configuration of the multiplexer 112 in the middle forms a series of Z E3 The overall signal path (parallel Z) E4 (Z in series) 机体 (Z) E1 and Z E2 (Parallel connection). The branch with electrode 104 and pin CE0 is connected to the input of current measurement circuit 126. The branch with electrode 106 and pin AIN2 is connected to the input of current measurement circuit 126. The branch with electrode 108 and pin AIN3 is connected to the output of signal generator 116. The branch with electrode 110 and pin AIN1 is connected to the input of current measurement circuit 126. Current I3 is measured, and voltage V is measured. CAL This forms Equation 14, as shown below. Equation 14 encapsulates the measurement current I3 and the measurement voltage V. CAL The relationship between the unknown impedance and the signal path from signal generator 116 to current measurement circuit 126 (as determined by multiplexer 112 in...) Figure 13 (Formed in the configuration shown).

[0060] exist Figure 14 In this circuit, multiplexer 112 is configured to couple signal paths from pin AIN1 to signal generator 116, signal paths from pin CE0 to current measurement circuit 126, signal paths from pin AIN2 to current measurement circuit 126, and signal paths from pin AIN3 to current measurement circuit 126. The current measured by current measurement circuit 126 is I4. Figure 14 The configuration of the multiplexer 112 in the middle forms a series of Z E4 The overall signal path (parallel Z) E3 (Z in series) 机体 (Z) E1 and Z E2(Parallel connection). The branch with electrode 104 and pin CE0 is connected to the input of current measurement circuit 126. The branch with electrode 106 and pin AIN2 is connected to the input of current measurement circuit 126. The branch with electrode 108 and pin AIN3 is connected to the input of current measurement circuit 126. The branch with electrode 110 and pin AIN1 is connected to the output of signal generator 116. Current I4 is measured, and voltage V is measured. CAL This leads to Equation 15, as shown below. Equation 15 encapsulates the measurement current I4 and the measurement voltage V. CA L connects to the signal generator 116 and the current measurement circuit 126 (from... Figure 14 The relationship between the unknown impedances in the entire signal path (formed by the multiplexer 112 in the configuration shown).

[0061] exist Figure 15 In this configuration, multiplexer 112 is configured to couple a signal path from pin CE0 to signal generator 116, a signal path from pin AIN2 to signal generator 116 (and), a signal path from pin AIN3 to current measurement circuit 126, and a signal path from pin AIN1 to current measurement circuit 126. The current measured by current measurement circuit 126 is I5. Figure 15 The configuration of the multiplexer 112 in the middle forms an overall signal path, which includes (Z) E1 and Z E2 (parallel) and Z 机体 Series and with (Z) E3 and Z E4 (Parallel) Series. The branch with electrode 104 and pin CE0 is connected to the output of signal generator 116. The branch with electrode 106 and pin AIN2 is connected to the output of signal generator 116. The branch with electrode 108 and pin AIN3 is connected to the input of current measurement circuit 126. The branch with electrode 110 and pin AIN1 is connected to the input of current measurement circuit 126. Measured current I5, measured voltage V CAL This forms Equation 16, as shown below. Equation 16 encapsulates the measurement current I5 and the measurement voltage V. CAL From signal generator 116 to current measurement circuit 126 (by...) Figure 15 The relationship between the unknown impedances in the entire signal path (formed by the multiplexer 112 in the configuration shown).

[0062] Figure 15An alternative signal path is to connect the branch with electrode 104 and pin CE0, 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.

[0063]

[0064]

[0065] Equation 17-21 shows an extended form of Equation 12-16 based on the notation of parallel impedance.

[0066] Using five equations (Equations 12-16) and five unknown impedances Z 机体 Z E1 Z E2 Z E3 and Z E4 It can derive and determine five unknown impedances Z. 机体 Z E1 Z E2 Z E3 and Z E4 The value of . For example Figure 11-15 As shown, each unique signal path includes all unknown impedances. Furthermore, as... Figure 5 , 7 As shown in Figure 8, each of the unique signal paths may include 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.

[0067] Algebraic operations can be applied to Equation 17-21 to rewrite Equation 12-21, such that the unknown impedance Z... 机体 Z E1 Z E2 Z E3 and Z E4 Based on the measured current values ​​(e.g., I1, I2, I3, I4, and I5), the measured current I CAL and R CAL The known resistance value is defined. The following pseudocode can be implemented in digital circuits 190, such as microcontrollers or microprocessors, to be based on... Figure 4 and 11 The measurements seen in -15 are used to determine and calculate unknown impedances.

[0068]

[0069] Can be executed in any order Figure 4 and11 The measurements seen in -15. In some cases, more than five measurements can be performed to generate more than five equations.

[0070] Figure 4 and 11 The scheme shown in -15 can have several advantages (similar to...). Figure 4-9 (The scheme shown). Note that it is no longer necessary to cross the unknown bioimpedance Z. 机体 Voltage measurement (which is usually in) Figure 1 (Required in the four-wire impedance measurement shown). As a result, the expensive inAmp120 is no longer needed in circuit 150. Furthermore, since no voltage measurement is performed, errors are avoided due to the grounding capacitance of pins AIN2 and AIN3 (used as low-pass filters), which results in V... A voltage and V C Different, V B voltage and V D (The voltages are different) are no longer relevant. Furthermore, this scheme can efficiently and accurately derive the five impedances Z. 机体 Z E1 Z E2 Z E3 and Z E4 In addition to these advantages, the scheme can now ensure accuracy even in the presence of large imbalances between high impedance and contact resistance.

[0071] Other technological advantages

[0072] Measuring bioimpedance is particularly useful for measuring bodily impedances used to detect lung fluid levels or to measure thoracic impedance. Bioimpedance measurement can also be used in electrical impedance tomography to non-invasively determine the composition of the body (e.g., imaging of tissues and bones) by taking bioimpedance measurements at different frequencies. Bioimpedance measurement can be used to measure respiratory activity, which can be obtained by observing changes in thoracic impedance. Measuring both bioimpedance and contact impedance means that respiratory activity can be obtained even in the presence of movement, as changes in contact impedance can be taken into account. Users such as athletes and patients can greatly benefit from these applications.

[0073] Besides the unknown bioimpedance Z 机体 In addition, the known contact impedance Z E1 Z E2 Z E3 and Z E4 This allows circuits to infer whether the contact (i.e., the contact formed by the electrodes on the contact body) is good, for example, as part of a diagnostic process. For instance, high contact resistance can indicate that the patch / electrode is not properly attached to the body. Therefore, information about the contact quality can be inferred from the derived contact resistance.

[0074] For example, digital circuit 190 can determine the quality of the contacts corresponding to the four electrodes based on the impedance of the four branches. If a given impedance of a branch is too high, digital circuit 190 can infer that the contact of that branch is bad and output a signal indicating the presence of a bad contact, and optionally output an identifier identifying which contact is bad. Digital circuit 190 can compare the impedance of the four branches with a predetermined threshold to determine whether a given impedance is too high.

[0075] User feedback can be provided based on inferred information about contact quality. In another example, a smart drug delivery application might require proper contact with the body to ensure correct and effective drug delivery. Improper contact can lead to poor absorption and drug buildup on the skin. Other applications, such as electrocardiograms or defibrillation, may also require proper contact with the body. Being able to infer contact quality based on derived contact impedance can provide users with feedback on the quality of contact in this context.

[0076] Some efforts to extract contact quality or contact impedance have limitations, and the scheme described herein for measuring impedance can improve upon these efforts. In some systems, efforts to extract contact quality or contact impedance ignore bioimpedance or assume that bioimpedance is zero, close to zero, or very small compared to contact impedance. This assumption is reasonable when electrodes measure the electrical activity of the heart, since in this case the electrodes are placed close to each other (e.g., on the chest) and the skin is prepared to make the body impedance very small. The impedance measurement scheme described herein does not make such an assumption. It may be beneficial not to make this assumption when the body impedance may be large. For example, when electrodes are placed on other parts of the body that are far apart from each other, the body impedance cannot be ignored, where the bioimpedance can be in the range of the contact impedance. In another example, if the electrodes have very low impedance, the bioimpedance can be much greater than the contact impedance. In yet another example, the lack of skin preparation can also make the contact impedance much greater than the bioimpedance being measured. For all these reasons, the impedance measurement scheme described herein can be used in a variety of situations. For example, the impedance measurement scheme can be used to non-invasively obtain the composition of the body, determine chest impedance, determine respiratory activity under exercise, etc.

[0077] Methods for measuring impedance

[0078] Figure 16This is a flowchart illustrating a method for measuring impedance according to some embodiments of the present disclosure. The impedance includes biological impedance and four branch impedances. In 1602, circuitry such as multiplexer 112 can form unique signal paths. In 1604, current measurement circuitry 126 can perform current measurements on the unique signal paths. The unique signal paths establish a set of equations that can derive the impedance. To ensure that the set of equations will produce an unknown impedance, each unique signal path includes at least some of the said impedances, and each unique signal path includes each impedance at least once. In 1606, digital circuitry 190 can derive the impedance based on the current measurement.

[0079] example

[0080] Example 1 is a method for measuring impedance, comprising: forming unique signal paths, wherein each unique signal path includes at least some of the impedance, the unique signal path including each impedance at least once, and the impedance including bio-impedance and four branch impedances; performing a current measurement of the unique signal paths; and deriving the impedance based on the current measurement.

[0081] In Example 2, the method of Example 1 may optionally include: deriving a voltage from the signal generator by applying the output of the signal generator to a resistor having a known resistance value and measuring the current through the resistor, and further deriving the impedance based on the voltage from the signal generator.

[0082] In Example 3, the method of Example 1 or 2 may optionally include: forming a signal path includes: controlling a configurable network to connect the output of the signal generator to the unique signal path and to connect the input of the current measurement circuit to the unique signal path.

[0083] In Example 4, the method of any one of Examples 1-3 may optionally include: performing current measurement by: applying a signal from a signal generator to the unique signal path, and measuring the current through each unique signal path by a current measurement circuit.

[0084] In Example 5, the method of any of Examples 1-4 may optionally include: each unique signal path includes two branch impedances.

[0085] In Example 6, the method of any one of Examples 1-5 may optionally include: each of the unique signal paths includes bioimpedance and two branch impedances.

[0086] In Example 7, the method of any of Examples 1-6 may optionally include: each unique signal path includes a network of all impedances.

[0087] Example 8 is a circuit for measuring impedance, comprising: a signal generator for generating a signal at the output of the signal generator; a current measuring circuit for measuring a current at an input of the current measuring circuit; a configurable network for connecting the output of the signal generator to the input of the current measuring circuit via unique signal paths, wherein each unique signal path includes at least some of the following: bioimpedance and branch impedance; and digital circuitry for determining the bioimpedance and the branch impedance based on the current measurement of the unique signal path.

[0088] In Example 9, the circuit of Example 8 may optionally include: a configurable network connecting the output of a signal generator to the input of a current measurement circuit via at least five unique signal paths, and the current measurement circuit measuring at least five current measurements.

[0089] In Example 10, the circuit of Example 8 or 9 may optionally include: digital circuitry determining the bioimpedance and four branch impedances based on at least five current measurements of the unique signal path.

[0090] In Example 11, the circuit of any one of Examples 8-10 may optionally include: a unique signal path that includes each of the bioimpedance and the branch impedance at least once.

[0091] In Example 12, the circuit of any of Examples 8-11 may optionally include: each unique signal path includes two branch impedances.

[0092] In Example 13, the circuit of any of Examples 8-12 may optionally include: each of some of the unique signal paths including bio-impedance and two branch impedances.

[0093] In Example 14, the circuit of any of Examples 8-13 may optionally include: each unique signal path comprising a network of all bioimpedances and branch impedances.

[0094] In Example 15, the circuit of any one of Examples 8-14 may optionally include: the configurable network further connecting the output of the signal generator to the input of the current measurement circuit via a resistor having a known resistance value, and the current measurement circuit further measuring the current through the resistor to determine the voltage from the signal generator.

[0095] Example 16 is 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 for applying a signal to at least five unique impedance networks and performing current measurements on the at least five unique impedance networks, wherein each unique impedance network has at least two of the four branches; and digital circuitry for deriving the bioimpedance and the impedance of the four branches based on the current measurements.

[0096] In Example 17, the circuit of Example 16 may optionally include: each unique impedance network includes all four branches.

[0097] In Example 18, the circuit of Example 16 or 17 may optionally include: at least five unique impedance networks including such unique impedance networks having one of the four branches connected to the signal generator and the other three of the four branches connected to the current measurement circuit.

[0098] In Example 19, the circuit of any one of Examples 16-18 may optionally include: at least five unique impedance networks including a second unique impedance network having two of the four branches connected to the signal generator and another two of the four branches connected to the current measurement circuit.

[0099] In Example 20, the circuit of any one of Examples 16-19 may optionally include: a circuit for further connecting the output of the signal generator to the input of the current measuring circuit via a resistor having a known resistance value, and further measuring the current through the resistor to determine the measured voltage from the signal generator.

[0100] In Example 21, the circuit of any one of Examples 16-20 may optionally include: a digital circuit determining the contact quality corresponding to the four electrodes based on the impedance of the four branches.

[0101] In Example 22, the circuit of any of Examples 16-21 may optionally include: a unique impedance network that includes at least one bioimpedance and each of the four branches of impedance.

[0102] In Example 23, the circuit of any of Examples 16-22 may optionally include: each of some of the unique impedance networks includes bioimpedance and the impedance of two of the four branches.

[0103] In Example 24, the circuit of any of Examples 16-23 may optionally include: each unique impedance network comprising a network of all bioimpedances and four branches of impedance.

[0104] Changes and Implementation

[0105] The unique signal path shown in this disclosure is not intended to be limiting. Other topologies and schemes for exciting and measuring signal paths can be implemented, and these schemes are contemplated in this disclosure.

[0106] Furthermore, some of the embodiments discussed above can be provided in digital signal processing technologies used in medical imaging, patient monitoring, medical instruments, and home healthcare. The embodiments described herein can also be beneficial for other applications requiring precise impedance measurements using at least four electrodes.

[0107] In the discussion of the above embodiments, various electrical components can be easily replaced, substituted, or otherwise modified to suit specific circuit requirements. Furthermore, it should be noted that the use of complementary electronic devices, hardware, software, etc., provides equally feasible options for implementing the teachings of this disclosure.

[0108] Various circuits used to derive unknown impedance may include portions of electronic circuitry that perform the functions described herein. In some cases, one or more portions of the circuitry may be provided by a processor specifically configured to perform the functions described herein. For example, the processor may include one or more dedicated components, or may include programmable logic gates configured to perform the functions described herein. The circuitry may operate in the analog, digital, or mixed-signal domain. In some cases, the 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 include means for performing or implementing one or more functions described herein.

[0109] It should also be noted that all specifications, dimensions, and relationships (e.g., number of processors, logical operations, etc.) outlined herein are provided for illustrative and educational purposes only. Such information may be significantly altered without departing from the spirit of this disclosure. These specifications are applicable only to a non-limiting example and should therefore be interpreted as such. Examples have been described in the foregoing description with reference to specific processor and / or component arrangements. Various modifications and changes may be made to such embodiments without departing from the scope of this disclosure. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

[0110] Note that interactions can be described using two, three, four, or more electronic components, utilizing the numerous examples provided herein. However, this is merely for clarity and illustration. It should be understood that systems can be combined in any suitable manner. Along similar design alternatives, any components, modules, and elements shown in the figures can be combined in a wide variety of 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 set of processes by referring only to a limited number of electrical components. It should be understood that the figures and the circuits they teach are easily expandable and can accommodate a large number of parts, as well as more complex / complex arrangements and configurations. Therefore, the examples provided should not limit the scope or inhibit the extensive teachings that may be applied to circuits of countless other architectures.

[0111] Note that in this specification, references to various features (e.g., elements, structures, modules, components, steps, operations, characteristics, etc.) included in “one embodiment,” “example embodiment,” “embodiment,” “another embodiment,” “some embodiments,” “various embodiments,” “other embodiments,” “alternative embodiments,” etc., are intended to indicate that any such feature is included in one or more embodiments of this disclosure, but may or may not be combined in the same embodiments.

[0112] It is equally important to note that the functions related to deriving the unknown impedance are only some of the possible functions that can be performed by or within the system shown in the figures. Some of these operations can be removed or eliminated where appropriate, or these operations can be significantly modified or changed without departing from the scope of this disclosure. Furthermore, the timing of these operations can vary considerably. The preceding operational flow is provided for illustrative and discussion purposes. The embodiments described herein offer substantial flexibility, as any suitable arrangement, timing sequence, configuration, and timing mechanism can be provided without departing from the teachings of this disclosure.

Claims

1. A circuit for measuring impedance, comprising: A signal generator, used to generate a signal at its output. A measurement circuit for performing measurements at its input. A configurable network is used to couple the output of the signal generator to the input of the measurement circuit via at least five unique signal paths, wherein each unique signal path forms a network with an impedance of interest and four branch impedances. Digital circuitry for determining the impedance of interest and the four branch impedances based on at least five measurements of the unique signal path performed by the measurement circuitry and calibration measurements of the signal generator.

2. The circuit of claim 1, wherein one of the unique signal paths comprises two branch impedances of the parallel-coupled branch impedances.

3. The circuit of claim 1, wherein one of the unique signal paths comprises two branch impedances of the branch impedances coupled in parallel to each other, and the two branch impedances coupled in parallel are connected in series with the impedance of interest.

4. The circuit according to claim 1, wherein: The first and second branch impedances of the four branch impedances are coupled to the first terminal of the impedance of interest. The third and fourth branch impedances of the four branch impedances are coupled to the second terminal of the impedance of interest, and For a unique signal path within a unique signal path: The first branch impedance of the four branch impedances is coupled to the output of the signal generator, and The second, third, and fourth branch impedances of the four branch impedances are coupled to the input of the measurement circuit.

5. The circuit according to claim 1, wherein: The first and second branch impedances of the four branch impedances are coupled to the first terminal of the impedance of interest. The third and fourth branch impedances of the four branch impedances are coupled to the second terminal of the impedance of interest, and For a unique signal path within a unique signal path: The second branch impedance of the four branch impedances is coupled to the output of the signal generator, and The first, third, and fourth branch impedances of the four branch impedances are coupled to the input of the measurement circuit.

6. The circuit according to claim 1, wherein: The first and second branch impedances of the four branch impedances are coupled to the first terminal of the impedance of interest. The third and fourth branch impedances of the four branch impedances are coupled to the second terminal of the impedance of interest, and For a unique signal path within a unique signal path: The third branch impedance of the four branch impedances is coupled to the output of the signal generator, and The first, second, and fourth branch impedances of the four branch impedances are coupled to the input of the measurement circuit.

7. The circuit according to claim 1, wherein: The first and second branch impedances of the four branch impedances are coupled to the first terminal of the impedance of interest. The third and fourth branch impedances of the four branch impedances are coupled to the second terminal of the impedance of interest, and For a unique signal path within a unique signal path: The fourth branch impedance of the four branches is coupled to the output of the signal generator, and The first, second, and third branch impedances of the four branch impedances are coupled to the input of the measurement circuit.

8. The circuit according to claim 1, wherein: The first and second branch impedances of the four branch impedances are coupled to the first terminal of the impedance of interest. The third and fourth branch impedances of the four branch impedances are coupled to the second terminal of the impedance of interest, and For a unique signal path within a unique signal path: The first and second branch impedances of the four branch impedances are coupled to the output of the signal generator, and The third and fourth branch impedances of the four branch impedances are coupled to the input of the measurement circuit.

9. An integrated circuit for measuring impedance, comprising: The first and second pins can be electrically coupled to the first end of the impedance of interest. The third and fourth pins can be electrically coupled to the second terminal of the impedance of interest. A signal generator, used to generate a signal at its output. A measurement circuit for performing measurements at its input. A configurable network electrically couples each of a first, second, third, and fourth pin to the output of the signal generator or the input of the measurement circuit to form at least five unique closed circuits, each having a first, second, third, and fourth pin and an impedance of interest. Digital circuitry is used to determine the four branch impedances associated with the first, second, third, and fourth pins, as well as the impedance of interest, based on at least five measurements of the unique closed circuit performed by the measurement circuitry and calibration measurements of the signal generator.

10. The integrated circuit of claim 9, wherein one of the unique closed circuits comprises two branch impedances in parallel coupled branch impedances.

11. The integrated circuit of claim 9, wherein one of the unique closed circuits comprises two branch impedances of the branch impedances coupled in parallel to each other, and the two branch impedances coupled in parallel are connected in series with the impedance of interest.

12. The integrated circuit according to claim 9, wherein, For one of the unique closed circuits mentioned above. The first pin is electrically coupled to the output of the signal generator, and Pins 2, 3, and 4 are electrically coupled to the input of the measurement circuit.

13. The integrated circuit according to claim 9, wherein, For one of the unique closed circuits mentioned above. The second pin is electrically coupled to the output of the signal generator, and Pin 1, pin 3, and pin 4 are electrically coupled to the input of the measurement circuit.

14. The integrated circuit according to claim 9, wherein, For one of the unique closed circuits mentioned above. The third pin is electrically coupled to the output of the signal generator, and The first, second, and fourth pins are electrically coupled to the input of the measurement circuit.

15. The integrated circuit according to claim 9, wherein, For one of the unique closed circuits mentioned above. The fourth pin is electrically coupled to the output of the signal generator, and The first, second, and third pins are electrically coupled to the input of the measurement circuit.

16. The integrated circuit according to claim 9, wherein, For one of the unique closed circuits mentioned above. The first and second pins are electrically coupled to the output of the signal generator, and Pins 3 and 4 are electrically coupled to the input of the measurement circuit.

17. A method for measuring impedance, said impedance including an impedance of interest and four branch impedances, the method comprising: Five unique signal paths with all impedances are formed, wherein forming each unique signal path includes: (1) coupling a signal generator to a subset of four branches, and (2) coupling the remaining branches of the four branches that are not in the subset to the measurement circuit. Five measurements of the unique signal path are performed via the measurement circuit, wherein each measurement includes: (1) applying a signal to a subset of the four branches coupled to the signal generator, and (2) measuring the remaining branches coupled to the measurement circuit. Impedance was derived based on five measurements.

18. The method of claim 17, wherein forming the five unique signal paths includes controlling a configurable network to couple each branch to the signal generator or the measurement circuit, the signal generator being coupled to at least one branch and the measurement circuit being coupled to at least two branches.

19. The method of claim 17, wherein forming the five unique signal paths does not involve grounding any of the four branches.

20. The method of claim 17, wherein the derived impedance is further based on calibration measurements of the signal generator.

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