High precision impedance measurement

Abstract

A measurement circuit (300) is provided. The measurement circuit (300) includes a control engine (320). An excitation source (302) is coupled to the control engine (320). A first electrode set (322, 326) and a second electrode set (324, 328) are coupled to the excitation source (302) and receive current from the excitation source (302). The control engine (320) operates the excitation source (302) in a first mode and a second mode. In the first mode, the control engine (320) measures a parasitic impedance associated with the first electrode set (322, 326) and the second electrode set (324, 328), and in the second mode, the control engine (320) measures an impedance of the first electrode set (322, 326) and the second electrode set (324, 328) and an impedance of an external object (350).

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Indian Provisional Patent Application No. 201941026256, filed on July 1, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application generally relates to biometric monitoring devices, and more specifically to a measurement circuit in a biometric monitoring device for accurately measuring the impedance of a biological object. Background Technology

[0004] Due to the use of impedance measurement of biological objects, including the human body, in a variety of clinical applications, there is increasing interest in it. Human impedance is already widely used clinically in various fields, including nutrition, body composition analysis, kidney disease, gastrointestinal disease, obesity analysis, and other critical medical applications. Many ongoing studies aim to provide accurate impedance measurements using methods that are low-cost, rapid, and safe compared to traditional approaches.

[0005] Measuring human body impedance involves attaching electrodes to the skin. In some systems, four electrodes are attached to different parts of the body. The electrodes are connected to an impedance measuring instrument. Current flows through the electrodes to the body, and the impedance measuring instrument measures and analyzes the voltage difference across the electrodes to generate the body's impedance value.

[0006] When the impedance of the electrode is lower than the parasitic impedance associated with the electrode, the measured value of human body impedance is quite accurate. However, when the impedance of the electrode is high and comparable to the parasitic impedance, the measured value of human body impedance is inaccurate, and the error can be as high as ten times the accurate value. This error is particularly noticeable in wearable biometric monitoring devices, in which the impedance of the contact electrodes is very high, comparable to the parasitic impedance. Summary of the Invention

[0007] According to one aspect of this disclosure, a measurement circuit is disclosed. The measurement circuit includes a control engine. An excitation source is coupled to the control engine. A first electrode group and a second electrode group are coupled to and receive current from the excitation source. The control engine operates the excitation source in a first mode and a second mode. In the first mode, the control engine measures the parasitic impedance associated with the first and second electrode groups, while in the second mode, the control engine measures the impedance of the first and second electrode groups as well as the impedance of an external object. Attached Figure Description

[0008] Figure 1 This is a block diagram illustrating a measurement circuit according to one embodiment.

[0009] Figure 2This is a block diagram illustrating a measurement circuit according to one embodiment.

[0010] Figure 3 This is a block diagram illustrating a measurement circuit according to one embodiment.

[0011] Figure 4 This is a flowchart illustrating an operation method of a measurement circuit according to one embodiment.

[0012] Figure 5 It is a biometric monitoring device according to one embodiment. Detailed Implementation

[0013] Figure 1 This is a block diagram illustrating a measurement circuit 100 according to one embodiment. The measurement circuit 100 includes an excitation source 102, a pair of resistors Rs 108, a first multiplexer MUX1 110, and an electrode group represented as a first electrode E1 122, a second electrode E2 124, a third electrode E3 126, and a fourth electrode E4 128. The measurement circuit 100 also includes a second multiplexer MUX2 130 and a control engine 120. The first electrode E1 122, the second electrode E2 124, the third electrode E3 126, and the fourth electrode E4 128 are coupled to the first multiplexer MUX1 110 and the second multiplexer MUX2 130.

[0014] Control engine 120 includes analog processing block 112, analog-to-digital converter (ADC) 114, digital processing block 116, and processor 118. Analog processing block 112 is coupled to a second multiplexer MUX2 130. ADC 114 is coupled to analog processing block 112. Digital processing block 116 is coupled between ADC 114 and processor 118. Processor 118, digital processing block 116, ADC 114, analog processing block 112, excitation source 102, first multiplexer MUX1 110, and second multiplexer MUX2 130 are all coupled to each other via a common connection path 152.

[0015] The parasitic impedance associated with each electrode in this electrode group is denoted as the first parasitic impedance Cp1 132, the second parasitic impedance Cp2 134, the third parasitic impedance Cp3 136, and the fourth parasitic impedance Cp4 138. For ease of illustration, the parasitic impedance is represented as a capacitor. The parasitic impedance is generated due to the wiring on the board or PCB on which the measurement circuit 100 is placed, and is typically on the order of picafarads.

[0016] The first parasitic impedance Cp1 132 is associated with the first electrode E1 122, and the second parasitic impedance Cp2 134 is associated with the second electrode E2 124. The third parasitic impedance Cp3 136 is associated with the third electrode E3 126, and the fourth parasitic impedance Cp4 138 is associated with the fourth electrode E4 128.

[0017] The impedance of the external object is Zb 150. In one example, the external object is a human body. In another example, the external object is a biological object. In yet another example, the external object is any non-living artifact. When the external object is coupled to the electrode group in the measurement circuit 100, a network is formed between the external object and the measurement circuit 100. Due to the contact between the electrodes and the external object, this network includes multiple impedances. ZE1 142 represents the impedance associated with the first electrode E1 122, ZE2 144 is the impedance associated with the second electrode E2 124, ZE3 146 represents the impedance associated with the third electrode E3 126, and ZE4 148 represents the impedance associated with the fourth electrode E4 128. The measurement circuit 100 may include one or more additional components known to those skilled in the art, and for simplicity, the measurement circuit 100 is not discussed here. Now in conjunction with Figure 2 and Figure 3 Explain the operation of measurement circuit 100.

[0018] Figure 2 This is a block diagram illustrating a measurement circuit 200 according to one embodiment. Measurement circuit 200 is similar to measurement circuit 100, and the operation of measurement circuit 100 is explained. In measurement circuit 100, control engine 120 operates excitation source 102 in a first mode and a second mode. Operation in the first mode is achieved through… Figure 2 To explain, the operation in the second mode is through Figure 3 To explain.

[0019] The connection of measurement circuit 200 is similar to that of measurement circuit 100, and for the sake of brevity, the connection of measurement circuit 200 will not be discussed here. Measurement circuit 200 is not coupled to external objects. Therefore, in Figure 2 The impedance of the external object Zb and the impedance generated due to the contact between the electrode and the external object (ZE1 to ZE4) are not shown.

[0020] Control engine 220 operates excitation source 202 in a first mode and a second mode. In the first mode, control engine 220 configures excitation source 202 to provide current to a first electrode group. In one example, the first electrode group includes a first electrode E1 222 and a third electrode E3 226. Control engine 220 configures a first multiplexer MUX1 210 to provide current from excitation source 202 to the first electrode E1 222 and the third electrode E3 226. Excitation source 202 provides current to the first electrode E1 222, and this current traverses back to excitation source 202 through the third electrode E3 226.

[0021] Control engine 220 measures the voltage across the first electrode group. Control engine 220 measures the voltage at nodes N1 204 and N2 206, respectively, defined as V. N1 and V N2 The voltage. The control engine 220 also measures the voltage defined as V at the first electrode E1 222 and the third electrode E3 226. E1 and V E3 The voltage. The current through the first parasitic impedance Cp1 232 is measured as:

[0022]

[0023] The first parasitic impedance Cp1 232 is defined as:

[0024]

[0025] The current through the third parasitic impedance Cp3 236 is defined as:

[0026]

[0027] The third parasitic impedance Cp3 236 is defined as:

[0028]

[0029] Therefore, using the steps described above, the measurement circuit 200 measures the parasitic impedance associated with the first electrode group. The first parasitic impedance Cp1 232 is measured using Equation 2 via the measurement circuit 200, and the third parasitic impedance Cp3 236 is measured using Equation 4 via the measurement circuit 200.

[0030] Control engine 220 configures excitation source 202 to provide current to a second electrode group. In one example, the second electrode group includes a second electrode E2 224 and a fourth electrode E4 228. Control engine 220 configures a first multiplexer MUX1 210 to provide current from excitation source 202 to the second electrode E2 224 and the fourth electrode E4 228. Excitation source 202 provides current to the second electrode E2 224, and this current traverses back to excitation source 202 through the fourth electrode E4 228.

[0031] Control engine 220 measures the voltage across the second electrode group. The control engine 220 measures the voltage at nodes N1 204 and N2 206, which are respectively defined as V... N1 and V N2 The control engine 220 also measures the voltage defined as V at the second electrode E2 224 and the fourth electrode E4 228. E2 and V E4 The voltage. The current through the second parasitic impedance Cp2 234 is measured as:

[0032]

[0033] The second parasitic impedance Cp2 234 is defined as:

[0034]

[0035] The current through the fourth parasitic impedance Cp4 238 is defined as:

[0036]

[0037] The fourth parasitic impedance Cp4 238 is defined as:

[0038]

[0039] Therefore, using the steps described above, the measurement circuit 200 measures the parasitic impedance associated with the second electrode group. The second parasitic impedance Cp2 234 is measured by the measurement circuit 200 using Equation 6, and the fourth parasitic impedance Cp4 238 is measured by the measurement circuit 200 using Equation 8.

[0040] Regarding the operation of the control engine 120, the processor 118 configures the second multiplexer MUX2 130 to receive voltages measured at each of the first node N1 104, the second node N2 106, and the first electrode E1 122, the second electrode E2 124, the third electrode E3 126, and the fourth electrode E4 128. Each of these voltages is received by the analog processing block 112 to generate a first signal. The analog-to-digital converter (ADC) 114 generates a digital signal from the first signal, and the digital processing block 116 generates a second signal from the digital signal. The processor 118 processes the second signal corresponding to each voltage to measure the first parasitic impedance Cp1 232, the third parasitic impedance Cp3 236, the second parasitic impedance Cp2 234, and the fourth parasitic impedance Cp4 238.

[0041] Therefore, in the first mode, the measurement circuit 200 uses the voltage measured across the first and second electrode groups to measure the parasitic impedances Cp1 232 to Cp4 238. It should be understood that the electrode combinations in the first and second electrode groups can differ based on design requirements. Furthermore, the number of electrodes in the first and second electrode groups can vary depending on the application. Additionally, for illustrative purposes, the excitation source 202 is considered a voltage source. It should be understood that the excitation source 202 could also be a current source, in which case a pair of resistors Rs 208 would not be necessary, and the current through each parasitic impedance would be known for the excitation source 202. In this case, the control engine 220 would directly measure the voltage at each electrode.

[0042] Figure 3 This is a block diagram illustrating a measurement circuit 300 according to one embodiment. Measurement circuit 300 is similar to measurement circuit 100, and the operation of measurement circuit 100 is explained. In measurement circuit 100, control engine 120 operates excitation source 102 in a first mode and a second mode. Operation in the first mode is achieved through… Figure 2 To explain, the operation in the second mode is through Figure 3 To explain.

[0043] The connection of measurement circuit 300 is similar to that of measurement circuit 100, and for the sake of brevity, the connection of measurement circuit 300 will not be discussed here. Measurement circuit 300 is coupled to an external object. Therefore, Figure 3 The impedance of the external object Zb 350 and the impedance generated due to the contact between the electrode and the external object (ZE1 342 to ZE4 348) are shown.

[0044] Control engine 320 operates excitation source 302 in a first mode and a second mode. In the second mode, control engine 320 configures excitation source 302 to provide current to a first electrode group. In one example, the first electrode group includes a first electrode E1 322 and a third electrode E3 326. The second electrode group includes a second electrode E2 324 and a fourth electrode E4 328. Control engine 320 configures a first multiplexer MUX1 310 to provide current from excitation source 302 to the first electrode E1 322 and the third electrode E3 326. Excitation source 302 provides current to the first electrode E1 322, and this current traverses back to excitation source 302 through the third electrode E3 326.

[0045] The measurements taken by the control engine 320 at nodes N1 304 and N2 306 are defined as V, respectively. N1 and V N2 The control engine 320 measures the first voltage set across each electrode of the first and second electrode groups. The first voltage set is defined as V. 1E1 V 1E3 V 1E2 and V 1E4 V 1E1 It is the voltage at the first electrode E1 322, V 1E3 It is the voltage at the third electrode E3 326, V 1E2 It is the voltage at the second electrode E2 324, V 1E4 This is the voltage at the fourth electrode E4 328. The current through the first parasitic impedance Cp1 332 is measured as follows:

[0046]

[0047] The value of the first parasitic impedance Cp1 332 is obtained from Equation 2. The current through the third parasitic impedance Cp3 336 is defined as:

[0048]

[0049] The value of the third parasitic impedance Cp3 336 is obtained from Equation 4. The current through the impedance ZE1 342 associated with the first electrode E1 322 is defined as:

[0050]

[0051] The current through the impedance ZE3 346 associated with the third electrode E3 326 is defined as:

[0052]

[0053] The current through the impedance ZE2 344 associated with the second electrode E2 324 is defined as:

[0054]

[0055] The value of the second parasitic impedance Cp2 334 is obtained from Equation 6. The current through the impedance ZE4 348 associated with the fourth electrode E4 328 is defined as:

[0056]

[0057] The value of the fourth parasitic impedance Cp4 338 is obtained from Equation 8. The impedance ZE2344 associated with the second electrode E2 324 is measured and defined as follows:

[0058]

[0059] Similarly, the impedance ZE3 346 associated with the third electrode E3 326 was measured as follows:

[0060]

[0061] Control engine 320 configures excitation source 302 to provide current to a second electrode group including second electrode E2 324 and fourth electrode E4 328. Control engine 320 configures first multiplexer MUX1 310 such that current from excitation source 302 is provided to second electrode E2 324 and fourth electrode E4 328. Excitation source 302 provides current to second electrode E2 324, and this current traverses back to excitation source 302 through fourth electrode E4 328.

[0062] The measurements taken by the control engine 320 at nodes N1 304 and N2 306 are defined as V, respectively. N1 and V N2 The control engine 320 measures a second voltage set across each electrode in the first and second electrode sets. This second voltage set is defined as V. 2E1 V 2E3 V 2E2 and V 2E4 V 2E1 It is the voltage across the first electrode E1 322, V 2E3 It is the voltage on the third electrode E3326, V 2E2 It is the voltage across the second electrode E2 324, V 2E4 This is the voltage across the fourth electrode E4 328. The current through the second parasitic impedance Cp2 334 is measured as follows:

[0063]

[0064] The current through the fourth parasitic impedance Cp4 338 is defined as:

[0065]

[0066] The current through the impedance ZE2 344 associated with the second electrode E2 324 is defined as:

[0067]

[0068] The current through the impedance ZE4 348 associated with the fourth electrode E4 328 is defined as:

[0069]

[0070] The current through the impedance ZE1 342 associated with the first electrode E1 322 is defined as:

[0071]

[0072] The current through the impedance ZE3 346 associated with the third electrode E3 326 is defined as:

[0073]

[0074] The impedance ZE2 344 associated with the second electrode E2 324 was measured as follows:

[0075]

[0076] Similarly, the impedance ZE3 346 associated with the third electrode E3 326 is measured and defined as follows:

[0077]

[0078] The processor 318 in the control engine 320 measures the impedance ZE1 342 associated with the first electrode E1 322 using equations 15 and 23, as defined below:

[0079]

[0080] The processor 318 in the control engine 320 measures the impedance ZE4 348 associated with the fourth electrode E4 328 via equivalent equations 16 and 24, as defined below:

[0081]

[0082] Using equations 25 and 26, processor 318 measures the impedance Zb 350 of an external object, defined as follows:

[0083]

[0084] Regarding the operation of the control engine 320, the processor 318 configures the second multiplexer MUX2 330 to receive voltages measured at the first node N1 304, the second node N2 306, the first voltage group, and the second voltage group. Each of these voltages is sequentially received by the analog processing block 312 to generate a first signal. The analog-to-digital converter (ADC) 314 generates a digital signal from the first signal, and the digital processing block 316 generates a second signal from the digital signal. The processor 318 processes the second signal corresponding to each voltage to ultimately measure the impedance Zb 350 of the external object.

[0085] Therefore, in the first mode, the measurement circuit 300 measures the parasitic impedances Cp1 332 to Cp4 338 associated with electrodes E1 322 to E4 328, respectively. In the second mode, the measurement circuit 300 uses the parasitic impedances measured in the first mode, the first voltage group, and the second voltage group to measure the impedances ZE1 342 to ZE4 348 associated with electrodes E1 322 to E4 328 and the impedance Zb 350 of the external object, respectively.

[0086] It should be understood that the electrode combinations in the first and second electrode groups can differ based on design requirements. Furthermore, the number of electrodes in the first and second electrode groups can vary depending on the application. Additionally, for illustrative purposes, the excitation source 302 has been considered a voltage source. It should be understood that the excitation source 302 can also be a current source, in which case a pair of resistors Rs 308 would not be necessary.

[0087] Even when parasitic impedance or the impedance associated with each electrode is very high, the measurement circuit 300 provides an accurate measurement of the impedance Zb 350 of an external object. Furthermore, the measurement circuit 300 provides a mechanism for solving the simple linear equations shown in Equations 1 to 27 to obtain the impedance Zb 350 of the external object. Therefore, the complexity of solving nonlinear equations is avoided by the measurement circuit 300. The measurement circuit 300 has found applications in wearable and medical devices that require accurate impedance measurement of the human body.

[0088] Figure 4 This is a flowchart 400 illustrating an operation method of a measurement circuit according to one embodiment. (In conjunction with...) Figure 1 The measurement circuit 100 shown is used to explain the flowchart 400. As discussed, in conjunction with... Figure 2 and Figure 3The operation of measurement circuit 100 is illustrated. Therefore, measurement circuits 200 and 300 are also used to explain flowchart 400. In step 402, the excitation source supplies current to the first and second electrode groups in a first mode, where there is no external body connection. In step 404, the parasitic impedance associated with the first and second electrode groups is measured.

[0089] In measurement circuit 200, control engine 220 configures excitation source 202 to provide current to first electrode group in a first mode. In one example, the first electrode group includes a first electrode E1 222 and a third electrode E3 226. Control engine 220 measures the voltage at the first electrode E1 222 and the third electrode E3 226. Control engine 220 also measures the voltage at node N1 204 and node N2 206. These voltages are used to measure the first parasitic impedance Cp1 232 and the third parasitic impedance Cp3 236.

[0090] Control engine 220 configures excitation source 202 to supply current to the second electrode group. In one example, the second electrode group includes a second electrode E2 224 and a fourth electrode E4 228. Control engine 220 measures the voltage across the second electrode group. Control engine 220 also measures the voltages at nodes N1 204 and N2 206. These voltages are used to measure the second parasitic impedance Cp2 234 and the fourth parasitic impedance Cp4 238.

[0091] In step 406, the external object is coupled to the first electrode group and the second electrode group. Figure 3 In this circuit, the measurement circuit 300 is coupled to an external object. Therefore, the impedance Zb 350 of the external object and the impedances (ZE1 342 to ZE4 348) resulting from the contact between the electrodes and the external object are shown.

[0092] In step 408, the excitation source supplies current to the first and second electrode groups in a second mode. In step 410, the impedance associated with the first and second electrode groups and the external object is measured. In the second mode, the control engine 320 configures the excitation source 302 to supply current to the first electrode group. In one example, the first electrode group includes a first electrode E1 322 and a third electrode E3 326. The second electrode group includes a second electrode E2 324 and a fourth electrode E4 328. The control engine 320 measures the voltage at nodes N1 304 and N2 306. The control engine 320 measures a first set of voltages across each electrode in the first and second electrode groups.

[0093] Control engine 320 configures excitation source 302 to provide current to a second electrode group, which includes a second electrode E2 324 and a fourth electrode E4 328. Control engine 320 measures the current at nodes N1 304 and N2 306, respectively, defined as V. N1 and V N2 The control engine 320 measures the second voltage across each electrode in the first and second electrode groups.

[0094] The measurement circuit 300 uses parasitic impedance, a first voltage group, and a second voltage group in the first mode to measure the impedances ZE1 342 to ZE4 348 associated with electrodes E1 322 to E4 328 and the impedance Zb 350 of an external object, respectively.

[0095] Regarding the operation of the control engine 320, the processor 318 configures the second multiplexer MUX2 330 to receive voltages measured at the first node N1 304, the second node N2 306, the first voltage group, and the second voltage group. Each of these voltages is sequentially received by the analog processing block 312 to generate a first signal. The analog-to-digital converter (ADC) 314 generates a digital signal from the first signal, and the digital processing block 316 generates a second signal from the digital signal. The processor 318 processes the second signal corresponding to each voltage to ultimately measure the impedance Zb 350 of the external object.

[0096] Even with very high parasitic impedance or impedance associated with each electrode, the method shown in flowchart 400 provides an accurate measurement of the impedance Zb 350 of an external object. Moreover, this method provides a mechanism for solving simple linear equations to obtain the impedance Zb 350 of the external object. Therefore, the complexity of solving nonlinear equations is avoided by the method shown in flowchart 400. This method has found applications in wearable and medical devices requiring precise impedance measurements of the human body.

[0097] Figure 5 A biometric monitoring device 500 according to one embodiment is illustrated. In one example, the biometric monitoring device 500 is or is incorporated into a mobile communication device, such as a mobile phone, personal digital assistant, personal computer, or any other type of electronic system. In another example, the biometric monitoring device 500 is a portable personal health monitoring device. The biometric monitoring device 500 can be a wearable device or a non-wearable device. The biometric monitoring device 500 can be installed or be part of an electronic or mechanical device for human use. The biometric monitoring device 500 may include one or more additional components known to those skilled in the art, and are not discussed here for simplicity.

[0098] In some embodiments, the biometric monitoring device 500 includes a mega-storage unit or a system-on-a-chip (SoC) that includes a processing unit 512, such as a CPU (central processing unit). For example, the processing unit 512 may be a CISC (Complex Instruction Set Computer) CPU, a RISC (Reduced Instruction Set Computer) CPU, or a digital signal processor (DSP). The processing unit 512 is typically, but not necessarily, located on the biometric monitoring device 500.

[0099] The biometric monitoring device 500 also includes various sensors, including a height sensor 504, a motion sensor 506, a heart rate sensor 508, and a position sensor 510. For simplicity, the biometric monitoring device 500 may include... Figure 5 One or more of the types of biosensors, physiological sensors, and environmental sensors not mentioned in the document.

[0100] The biometric monitoring device 500 also includes a communication circuit 514. In one example, one or more of these sensors are located external to the biometric monitoring device 500. In this case, the biometric monitoring device 500 can communicate with these external devices using the communication circuit 514, which can be wired or wireless. It should be understood that the external device can be a smartphone with one or more sensors, and the biometric monitoring device 500 is capable of communicating with such a smartphone. All these variations and implementations should be understood to be within the scope of this disclosure.

[0101] The biometric monitoring device 500 includes a display 502. It should be understood that the display 502 may also be external to the biometric monitoring device 500. The biometric monitoring device 500 can collect one or more types of physiological and / or environmental data from embedded sensors and / or external devices and transmit such data to other devices. The data can be stored, processed, and visualized by the user on a computer, mobile phone, or health station.

[0102] The biometric monitoring device 500 includes a measurement circuit 520. The measurement circuit 520 is similar to the measurement circuit 100 in terms of connection and operation. The operation of the measurement circuit 520 is similar to that via… Figure 2 and Figure 3 The operation of measurement circuit 100 is explained. Measurement circuit 520 is similar to measurement circuit 100, including a control engine and an excitation source coupled to the control engine. Measurement circuit 520 also includes a first electrode group and a second electrode group.

[0103] An excitation source supplies current to a first electrode group and a second electrode group in a first mode. The parasitic impedance associated with the first and second electrode groups is measured. In measurement circuit 520, a control engine configures the excitation source to supply current to the first electrode group in the first mode. The control engine measures the voltage at the first electrode group. These voltages are used to measure the parasitic impedance associated with the first electrode group.

[0104] The control engine configures the excitation source to supply current to the second electrode group. The control engine measures the voltage across the second electrode group. These voltages are used to measure the parasitic impedance associated with the second electrode group.

[0105] In the second mode, an external object is coupled to the first and second electrode groups. In one instance, the external object is a biological object or a human body. In another example, the external object is any non-living artifact. An excitation source supplies current to the first and second electrode groups in the second mode. The impedance associated with the first and second electrode groups and the external object is measured.

[0106] In the second mode, the control engine configures the excitation source to supply current to the first electrode group. The control engine measures a first voltage group across each electrode in the first and second electrode groups. The control engine configures the excitation source to supply current to the second electrode group. The control engine measures a second voltage group across each electrode in the first and second electrode groups. The measurement circuit 520 uses the parasitic impedance, the first voltage group, and the second voltage group measured in the first mode to measure the impedance associated with the electrodes and the impedance of external objects.

[0107] Various sensors in the biometric monitoring device 500 generate sensing signals, and the processing unit 512 generates analysis parameters from the sensing signals. The analysis parameters are displayed on the display 502. The processing unit 512 also receives the impedance value of an external object from the measurement circuit 520 and displays it on the display 502.

[0108] Within the scope of the claims, modifications may be made to the described embodiments, and in other embodiments as well.

Claims

1. A measurement circuit comprising: a control engine; a stimulus source coupled to the control engine; and a first electrode set and a second electrode set coupled to the stimulus source and configured to receive current from the stimulus source, wherein the control engine is configured to operate the stimulus source in a first mode and a second mode, and wherein in the first mode the control engine is configured to measure a parasitic impedance associated with the first electrode set and the second electrode set, and in the second mode the control engine is configured to measure impedances of the first electrode set and the second electrode set and an impedance of an external object, wherein in the second mode: the control engine configures the stimulus source to provide current to the first electrode set; the control engine is configured to measure a first set of voltages across each electrode of the first electrode set and the second electrode set; the control engine configures the stimulus source to provide current to the second electrode set; and the control engine is configured to measure a second set of voltages across each electrode of the first electrode set and the second electrode set. the external object is coupled to the first electrode set and the second electrode set in the second mode.

2. The measurement circuit of claim 1, wherein, in the first mode:

3. The measurement circuit of claim 1, wherein, the control engine configures the stimulus source to provide current to the first electrode set; the control engine is configured to measure a voltage across each electrode of the first electrode set; the control engine configures the stimulus source to provide current to the second electrode set; and the control engine is configured to measure a voltage across each electrode of the second electrode set. the control engine is configured to measure the parasitic impedance associated with the first electrode set and the second electrode set by using the voltages measured across the first electrode set and the second electrode set. the control engine is configured to measure the impedances of the first electrode set, the second electrode set, and the external object using the first set of voltages, the second set of voltages, and the parasitic impedance.

4. The measurement circuit of claim 3, wherein, the control engine further comprises:

5. The measurement circuit of claim 1, wherein, an analog processing block coupled to the first electrode set and the second electrode set; 6. The measurement circuit of claim 1, wherein, an analog-to-digital converter (ADC) coupled to the analog processing block; a digital processing block coupled to the ADC; and a processor coupled to the digital processing block.

7. A method comprising: in a first mode, providing current from a stimulus source to a first electrode set and a second electrode set; measuring a parasitic impedance associated with the first electrode set and the second electrode set; coupling an external object to the first electrode set and the second electrode set; in a second mode, providing current from the stimulus source to the first electrode set and the second electrode set; measuring impedances of the first electrode set and the second electrode set and an impedance of the external object, wherein providing current to the first electrode set and the second electrode set in the second mode further comprises: providing current from the stimulus source to the first electrode set; measuring a first set of voltages across each electrode of the first electrode set and the second electrode set; ​ ​ providing current from the excitation source to the second electrode set; and measuring a second set of voltages across each electrode of the first electrode set and the second electrode set.

8. The method of claim 7, wherein, providing current to the first electrode set and the second electrode set in the first mode further comprises: providing current from the excitation source to the first electrode set; measuring a voltage across the first electrode set; providing current from the excitation source to the second electrode set; and measuring a voltage across the second electrode set.

9. The method of claim 8, wherein, measuring the parasitic impedance associated with the first electrode set and the second electrode set further comprises using the voltages measured across the first electrode set and the second electrode set.

10. The method of claim 7, wherein, measuring the impedance of the first electrode set and the second electrode set and the impedance of the external object further comprises using the first set of voltages, the second set of voltages, and the parasitic impedance.

11. The method of claim 10, wherein, measuring the impedance of the first electrode set and the second electrode set and the impedance of the external object further comprises: providing the first set of voltages and the second set of voltages to an analog processing block in sequence to generate a first signal; generating a digital signal from the first signal by an analog-to-digital converter (ADC); generating a second signal from the digital signal by a digital processing block; and processing the generated second signal in a processor in association with each voltage of the first set of voltages and the second set of voltages.

12. A biometric monitoring device comprising: a plurality of sensors configured to generate a sensing signal; a processing unit coupled to the plurality of sensors and configured to generate an analysis parameter from the sensing signal; a display coupled to the processing unit and configured to display the analysis parameter generated by the processing unit; and a measurement circuit coupled to the processing unit and the display, the measurement circuit comprising: a control engine; an excitation source coupled to the control engine; and a first electrode set and a second electrode set coupled to the excitation source and configured to receive current from the excitation source, wherein the control engine is configured to operate the excitation source in a first mode and a second mode, and wherein in the first mode, the control engine is configured to measure a parasitic impedance associated with the first electrode set and the second electrode set, and in the second mode, the control engine is configured to measure an impedance of the first electrode set and the second electrode set and an impedance of an external object, wherein, in the second mode: the control engine configures the excitation source to provide current to the first electrode set; the control engine is configured to measure a first set of voltages across each electrode of the first electrode set and the second electrode set; the control engine configures the excitation source to provide current to the second electrode set; and the control engine is configured to measure a second set of voltages across each electrode of the first electrode set and the second electrode set.

13. The biometric monitoring device of claim 12, wherein, in the second mode, the external object is coupled to the first electrode set and the second electrode set.

14. The biometric monitoring device of claim 12, wherein, in the first mode: the control engine configures the excitation source to provide current to the first electrode set; the control engine is configured to measure a voltage across each electrode of the first electrode set; the control engine is configured to measure a voltage across each electrode of the second electrode set. the control engine is configured to measure a voltage across each electrode of the first electrode set; the control engine is configured to measure a voltage across each electrode of the second electrode set.

15. The biometric monitoring device of claim 14, wherein, the control engine is configured to measure the parasitic impedance associated with the first electrode set and the second electrode set using the measured voltages across the first electrode set and the second electrode set.

16. The biometric monitoring device of claim 12, wherein, the control engine is configured to measure the impedance of the first electrode set, the second electrode set, and the external object using the first voltage set, the second voltage set, and the parasitic impedance.

17. The biometric monitoring device of claim 12, wherein, the control engine further comprises: an analog processing block coupled to the first electrode set and the second electrode set; an analog-to-digital converter (ADC) coupled to the analog processing block; a digital processing block coupled to the ADC; and a processor coupled to the digital processing block.

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