TWI752867B - Circuitry of a biopotential acquisition system - Google Patents

Abstract

The present invention provides a circuitry of a biopotential acquisition system, where the circuitry includes an input node, an ETI transmitter, a capacitor and an ETI receiver. The input node is configured to receive an input signal from an electrode of the biopotential acquisition system. The ETI transmitter is configured to generate a transmitter signal. A first node of the capacitor is coupled to the ETI transmitter, and a second node of the capacitor is coupled to the input node. The ETI receiver is coupled to the input node, and is configured to receive the transmitter signal via the capacitor to generate an ETI.

Description

Circuit of Biopotential Acquisition System

The present invention relates to an electronic circuit, and more particularly, to a circuit for a biopotential acquisition system.

Conventional medical devices typically use large dry electrodes or wet electrodes to measure physiological signals to obtain physiological characteristics such as bio-impedance or electrocardiograms. Recently, personal biosensors such as portable/wearable medical devices have become popular because they can provide physiological information at any time for user reference. Given the use and design of these portable medical devices, smaller dry electrodes are more suitable. However, smaller dry electrodes mean poor electrode impedance, and poor electrode impedance (ie, larger electrode impedance) may lead to false detection of electrocardiography (ECG) signals. Furthermore, this adds to the difficulty of measuring ECG signals since electrode-tissue impedance (ETI) can vary greatly due to contact factors or motion artifacts.

To address ECG signal issues in dry electrode applications, ETI is also detected to reduce motion artifacts in ECG signals. In conventional techniques, the current used for ETI measurement is injected into the electrodes, and the ETI receiver detects the voltage on the electrodes to determine the ETI. However, the injection of current into the electrodes in conventional techniques can It can induce additional noise at the electrodes, resulting in errors in the detection of the ECG signal. In addition, since the current generator with lower impedance is connected to the electrode, the strength of the ECG signal may be affected, and the input range of the ECG signal is narrowed.

Therefore, an object of the present invention is to provide a biopotential acquisition system that can accurately measure ECG signals while measuring ETI, so as to solve the above-mentioned problems.

According to an embodiment of the present invention, a circuit of a biopotential acquisition system is provided. The circuit includes an input node, an ETI transmitter, a capacitor, and an ETI receiver. The input node is configured to receive input signals from electrodes of the biopotential acquisition system. The ETI transmitter is configured to generate transmitter signals. A first node of the capacitor is coupled to the ETI transmitter, and a second node of the capacitor is coupled to the input node. The ETI receiver is coupled to the input node and is configured to receive the transmitter signal via the capacitor to generate the ETI.

In the biopotential acquisition system of the present invention, by designing a capacitor between the ETI transmitter and the input node of the biopotential acquisition system, the measurement of the ECG signal will not be affected when the ETI is measured. Therefore, the biopotential acquisition system can accurately measure ECG signal and ETI simultaneously.

These and other objects of the present invention will no doubt become apparent to those skilled in the art after reading the various drawings and the following detailed description of the preferred embodiments shown in the accompanying drawings.

100: Biopotential Acquisition System

102,104: Electrodes

110: ETI transmitter

120: ECG receiver

130: ETI receiver

112:DAC

114: Filter

122: Low Noise Amplifier

124: low pass filter

126: ADC

132_1: First amplifier

132_2: Second amplifier

134_1: first low pass filter

134_2: Second low pass filter

136: Multiplexer

138: ADC

202_1~202_N, 204_1~204_N: Current source

SW1_1~SW1_N, SW2_1~SW2_N: switch

C11_1~C11_N, C12_1~C12_N: capacitors

R11_1~R11_N, R12_1~R12_N: Resistors

The invention is shown by way of example and not limitation in the figures of the accompanying drawings, in which similar figures are attached. Symbols indicate similar elements. When a particular feature, structure or characteristic is described in connection with one embodiment, it should be considered that it is within the knowledge of those skilled in the art to implement such feature, structure or characteristic in connection with other embodiments, whether or not expressly indicated.

FIG. 1 is a schematic diagram illustrating a biopotential acquisition system according to an embodiment of the present invention.

Figure 2 shows a current DAC according to one embodiment of the present invention.

Figure 3 shows a capacitor DAC according to one embodiment of the present invention.

Figure 4 shows a resistor DAC according to one embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a filter according to one embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a filter according to another embodiment of the present invention.

Certain terms are used throughout the specification and claims to refer to particular elements. It should be understood by those skilled in the art that electronic device manufacturers may refer to the same element by different nouns. This specification and the scope of the patent application do not use the difference in name as a way to distinguish elements, but use the difference in function of the elements as a basis for differentiation. The "comprising" mentioned in the entire specification and the subsequent scope of the patent application is an open-ended term, so it should be interpreted as "including but not limited to". Furthermore, the term "coupled" herein includes any means of direct and indirect electrical connection. Therefore, if it is described herein that the first device is electrically connected to the second device, it means that the first device can be directly connected to the second device or indirectly connected to the second device through other devices or connecting means.

FIG. 1 is a schematic diagram illustrating a biopotential acquisition system 100 according to one embodiment of the present invention. As shown in FIG. 1, the biopotential acquisition system 100 is a two-electrode biopotential acquisition system having two electrodes 102 and 104 for connection to the right body (eg, the right hand) and the left body (eg, the left hand) ) to obtain the biopotential of the human body Signals, the biopotential acquisition system 100 can process and analyze the biopotential signals to determine physiological signals such as electrocardiogram (ECG) signals, and the physiological characteristics can be displayed on the screen of the biopotential acquisition system 100 . In this embodiment, the biopotential acquisition system 100 can be built in any portable electronic device or wearable electronic device.

The biopotential acquisition system 100 includes an ETI transmitter 110, an ECG receiver 120 and an ETI receiver 130, wherein the ETI transmitter 110 includes a digital-to-analog converter (DAC) 112 and a filter 114; the ECG receiver 120 includes a low noise amplifier 122, a low-pass filter (LPF) 124 and an analog-to-digital converter (ADC) 126; the ETI receiver 130 includes a first Amplifier 132_1 , second amplifier 132_2 with mixer, first low pass filter 134_1 , second low pass filter 134_2 , multiplexer (MUX) 136 and ADC 138 . In addition, the biopotential acquisition system 100 further includes a first capacitor C1 and a second capacitor C2, wherein a first node of the first capacitor C1 is coupled to the filter 114, and a second node of the first capacitor C1 is coupled to the biopotential acquisition system One input node of 100 (ie, the second node is coupled to electrode 104 and the negative input terminal of LNA 122); the first node of second capacitor C2 is coupled to filter 114, the second node of second capacitor C2 is coupled to filter 114 The node is coupled to another input node of the biopotential acquisition system 100 (ie, the second node is coupled to the electrode 102 and the positive input terminal of the low noise amplifier 122).

When electrodes 102 and 104 are attached to the human body, ETI is formed so that biopotential acquisition system 100 can have a large input impedance, which can vary greatly due to contact factors or motion artifacts. In the first embodiment illustrated in FIG. 1, the electrode 102/104 ETI impedance is modeled as a resistor and a capacitor C _EL R _EL are connected in parallel. In operation of the biopotential acquisition system 100, when the electrodes 102 and 104 are in contact with the human body and the biopotential acquisition system 100 begins to measure ECG signals, the low noise amplifier 122 of the ECG receiver 120 begins to receive the signal V _{IP from the electrodes 102 and 104} and V _IN (biopotential signal) to produce an amplified signal, and the amplified signal is processed by low pass filter 124 and ADC 126 to determine physiological information such as ECG signals. At this point, the input impedances (ie, R _EL and C _EL ) may vary greatly due to motion artifacts, so the ECG signal may be inaccurate. Therefore, in order to solve the ETI problem, at the same time, the ETI transmitter 110 and the ETI receiver 130 are controlled to determine the ETI, so that the biopotential acquisition system 100 notifies the user of the motion artifact problem or adjusts/compensates the ECG signal generated by the ECG receiver 120 .

Regarding the operation of the ETI transmitter 110, the DAC 112 receives the digitized ETI input signal Din to generate the analog ETI input signal, where the DAC 112 may be implemented by any suitable DAC, such as a current DAC, a capacitor DAC, or a resistor DAC. FIG. 2 shows a current DAC according to an embodiment of the present invention, wherein the current DAC includes a plurality of current sources 202_1 to 202_N and a plurality of current sources 204_1 to 204_N, and the plurality of current sources 202_1 to 202_N pass through a plurality of switches SW1_1 To SW1_N are selectively connected to the output node N _{DAC of the} DAC 112 , and the plurality of current sources 204_1 to 204_N are selectively connected to the output node N _{DAC of the} DAC 112 via the plurality of switches SW2_1 to SW2_N. FIG. 3 shows a capacitor DAC according to one embodiment of the present invention, wherein the capacitor DAC includes a plurality of capacitors C11_1 to C11_N and a plurality of capacitors C12_1 to C12_N, the plurality of capacitors C11_1 to C11_N are selectively via a plurality of switches SW1_1 to SW1_N The ground is connected to the output node N _{DAC of the} DAC 112 , and the plurality of capacitors C12_1 to C12_N are selectively connected to the output node N _{DAC of the} DAC 112 via the plurality of switches SW2_1 to SW2_N. FIG. 4 shows a resistor DAC according to an embodiment of the present invention, wherein the resistor DAC includes a plurality of resistors R11_1 to R11_N and a plurality of resistors R12_1 to R12_N, and the plurality of resistors R11_1 to R11_N are connected via a plurality of resistors R11_1 to R11_N. The switches SW1_1 to SW1_N are selectively connected to the output node N _{DAC of the} DAC 112 , and the plurality of resistors R12_1 to R12_N are selectively connected to the output node N _{DAC of the} DAC 112 via the plurality of switches SW2_1 to SW2_N.

In this embodiment, the frequency of the transmitter signal generated by the ETI transmitter 110 is higher than the ECG Signal. For example, the ECG signal frequency may be below a few hundred hertz, but the transmitter signal generated by the ETI transmitter 110 may be several kilohertz.

Referring next to FIG. 1, a filter 114 filters the analog ETI input signal to remove harmonic tones to generate a transmitter signal. FIG. 5 is a schematic diagram illustrating filter 114 according to one embodiment of the present invention. As shown in FIG. 5, filter 114 includes a capacitor C _F1 and a resistor R _F1 connected to a first output node of DAC 112, and filter 114 also includes a second output node connected to DAC 112 (eg, When the DAC 112 has a differential output signal, it may have a first output node and a second output node) capacitor C _F2 and resistor R _F2 . In the embodiment shown in Figure 5, if DAC 112 is implemented as a current DAC, capacitors C _F1 and C _{F2 are} used to remove higher order harmonics of the transmitter signal, and resistors R _F1 and R _{F2 are} used to convert the current signal Converted to a voltage signal. FIG. 6 is a schematic diagram illustrating a filter 114 according to another embodiment of the present invention. As shown in FIG. 6, the filter 114 is an active filter that includes an input resistor R _F4 , a feedback resistor R _F3 , a feedback capacitor _CF and an amplifier 610, wherein the input resistor R _{F4 is} connected between the DAC 112 and the amplifier between the input terminals of amplifier 610 , and the feedback resistor R _F3 and the feedback capacitor _CF are coupled in parallel between the input terminal and the output terminal of amplifier 610 .

Next, the filtered transmitter signal is received by the ETI receiver 130 after passing through capacitors C1 and C2. The ETI receiver 130 then receives the filtered transmitter signal to generate the ETI. Specifically, the ETI receiver 130 includes an in-phase path and a quadrature path, the in-phase path includes a first amplifier 132_1 with a mixer and a first low-pass filter 134_1, and the quadrature path includes a second amplifier 132_2 with a mixer and a first low-pass filter 134_1 The second low-pass filter 134_2. The first amplifier with mixer 132_1 is configured to mix the transmitter signal with the oscillating signal to generate a first mixed signal (low frequency or DC), and then the low pass filter 134_1 filters the first mixed signal to generate first filtered signal. The second amplifier 132_2 with the mixer is configured to mix the transmitter signal with the oscillating signal to generate a second mixed signal (low frequency or DC), then low The pass filter 134_2 filters the second mixed signal to generate a second filtered signal. The first filtered signal and the second filtered signal are then processed by multiplexer 136 and ADC 138 to generate ETI. In addition, since the operation of the ETI receiver 130 is known to those skilled in the art, and the present invention focuses on the ETI transmitter 110, the first capacitor C1 and the second capacitor C2, the ETI receiver 130 is omitted here. A detailed description.

Designing the first capacitor C1 and the second capacitor C2 between the input node of the biopotential acquisition system 100 and the ETI transmitter 110 can make the measurement of the ECG more accurate, and the input range of the _{input signals V IP} and V _{IN will not} narrow. Specifically, because the first capacitor C1 and the second capacitor C2 have large capacitances at lower frequencies, only a small fraction of the low frequency noise generated by the DAC 112 is delivered to the input node of the biopotential acquisition system 100, ie, The input signals V _IP and V _IN are only slightly affected by the low frequency noise generated by the DAC 112 . Furthermore, since the first capacitor C1 and the second capacitor C2 have large capacitances at lower frequencies, the input impedance (high impedance) of the ECG receiver 120 will not be affected by the ETI transmitter 110 . Additionally, since the first capacitor C1 and the second capacitor C2 have smaller capacitances at higher frequencies, the filtered transmitter signal can be sent to the ETI receiver 130 without suffering excessive losses. Further, since the input node of the biopotential acquisition system 100 is connected to the first capacitor C1 and the second capacitor C2, so the input signal V _IP and V _IN having a rail-to-rail range (rail-to-rail range) , i.e., biopotential acquisition The input range of the system 100 will not be affected.

In brief overview, in the biopotential acquisition system of the present invention, by designing a capacitor between the ETI transmitter and the input node of the biopotential acquisition system, the measurement of the ECG signal is not affected when ETI is measured. Therefore, the biopotential acquisition system can accurately measure ECG signal and ETI simultaneously.

Those skilled in the art will readily recognize that various modifications and variations can be made in the apparatus and method while maintaining the teachings of the present invention. Accordingly, the above disclosure should be construed as being limited only by the limits of the scope of the appended claims.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

100: Biopotential Acquisition System

102,104: Electrodes

110: ETI transmitter

120: ECG receiver

130: ETI receiver

112:DAC

114: Filter

122: Low Noise Amplifier

124: low pass filter

126: ADC

132_1: First amplifier

132_2: Second amplifier

134_1: first low pass filter

134_2: Second low pass filter

136: Multiplexer

138: ADC

Claims (10)

A circuit of a biopotential acquisition system, comprising: an input node configured to receive an input signal from an electrode of the biopotential acquisition system; an electrode tissue impedance (ETI) transmitter configured to generate a transmitter signal; and a capacitor, wherein the a first node of a capacitor coupled to the ETI transmitter, a second node of the capacitor coupled to the input node; and an ETI receiver coupled to the input node configured to receive via the capacitor the transmitter signal to generate the ETI. The circuit of claim 1, further comprising an electrocardiogram (ECG) receiver configured to receive the input signal to generate an ECG signal, wherein the ECG receiver and the ETI receiver operate simultaneously. The circuit of claim 1, wherein the transmitter signal is a voltage signal. The circuit of claim 1, wherein the frequency of the transmitter signal is higher than the frequency of the input signal. The circuit of claim 1, wherein the ETI transmitter comprises: a digital-to-analog converter (DAC) configured to receive a digital ETI input signal to generate an analog ETI input signal; and a filter configured to The analog ETI input signal is filtered to generate the transmitter signal to the first node of the capacitor. The circuit of claim 5, wherein the DAC is a current DAC and the filter filters and converts the analog ETI input signal to a voltage signal as the transmitter signal. The circuit of claim 6, wherein the filter comprises: a first resistor coupled between the output node of the DAC and a reference voltage; and a first capacitor coupled between the output node of the DAC and the reference voltage between the reference voltages. The circuit of claim 5, wherein the DAC is a capacitor DAC or a resistor DAC, and the filter filters the analog ETI input signal to generate the transmitter signal. The circuit of claim 5, wherein the filter is configured to filter out higher order harmonics of the transmitter signal. The circuit of claim 4, wherein the capacitance of the capacitor at the frequency of the transmitter signal is less than the capacitance of the capacitor at the frequency of the input signal.

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