A suspended electrode automatic zeroing circuit for contactless ECG monitoring

Abstract

The invention discloses a suspension electrode automatic zeroing circuit for contactless ECG monitoring, which includes a high-pass input stage circuit, an action interference suppression stage circuit and a switch zeroing circuit; the high-pass input stage circuit includes a suspension electrode, a low bias current operational amplifier circuit A1 and an active low-pass feedback module; the action interference suppression stage includes an operational amplifier A3, a resistor R2 and a capacitor C2, and its output end is connected to the reference level pin REF of the operational amplifier A1; the switch zeroing circuit includes a positive comparator A4, an inverting comparator A5, a zeroing switch S1 and a zeroing switch S2; the output end of the operational amplifier A3 is connected to the in-phase input end of the positive comparator A4 and the inverting input end of the inverting comparator A5; the output of the positive comparator A4 is connected to the control end of the zeroing switch S1, and the output end of the inverting comparator A5 is connected to the control end of the zeroing switch S2. When the output signal of the input stage of the measuring circuit is continuously saturated for a period of time, the invention can automatically zero and ensure the continuous ECG monitoring.

Description

[Technical field]

[0001] The invention belongs to the technical field of electrocardiogram monitoring circuits, and in particular relates to a suspension electrode automatic zeroing circuit for contactless electrocardiogram monitoring. [Background technology]

[0002] Dynamic ECG is a commonly used screening method for cardiovascular diseases in clinical practice. By recording the ECG signals of suspected patients in their natural living state for more than 24 hours, arrhythmia events and abnormal ST segment changes that are not easy to be found by conventional ECG can be found, and important diagnostic evaluation basis can be obtained. The ECG signal acquisition electrodes used in traditional ECG measurement are Ag / AgCl wet electrodes with conductive glue. This wet electrode needs to be cleaned with alcohol before use. The electrode is pressed against the human skin. It is not suitable for people with skin allergies, and cannot be reused. It is not suitable for long-term dynamic monitoring of human ECG signals, and the cost of long-term monitoring is high. Non-contact ECG monitoring avoids many problems of traditional lead contact, especially in terms of wearing comfort and applicability. Non-contact ECG monitoring is an innovative method for wearable and continuous ECG monitoring. Most non-contact ECG monitoring circuits use suspended electrodes to perform inductive measurement of ECG signals. The suspended electrodes form a capacitor with the ECG signal source to AC couple the ECG signal to the measurement circuit. The suspended electrode is generally connected to the input of the measurement circuit through a high-resistance path. Affected by the bias current, its potential will accumulate a large drift after the measurement circuit has been working for a period of time. When the drift exceeds the common-mode voltage range of the measurement circuit, the measurement circuit will enter saturation or cutoff, and ECG monitoring will be forced to stop.

[0003] At present, most circuits use a relatively simple zeroing method, that is, the zeroing switch is controlled by measuring the output voltage of the circuit itself. If the output is saturated, the switch is turned on to zero the voltage accumulated by the floating electrode drift. This method is not conducive to automation on the one hand. On the other hand, during the ECG monitoring process, the output voltage will be saturated with the movement of the human body, which leads to frequent zeroing of the floating electrode. Since the zeroing process will sacrifice the monitoring of one cardiac cycle, the frequent zeroing method is not conducive to continuous monitoring.

[0004] Therefore, it is necessary to provide a new automatic zeroing circuit for suspended electrodes used in contactless ECG monitoring to solve the above technical problems. [Summary of the invention]

[0005] The main purpose of the present invention is to provide a floating electrode automatic zeroing circuit for contactless ECG monitoring, which can automatically clear the output signal of the input stage of the measuring circuit after being saturated for a period of time, thereby ensuring the continuous ECG monitoring.

[0006] The present invention achieves the above-mentioned object through the following technical scheme: a suspended electrode automatic zeroing circuit for contactless ECG monitoring, which includes a high-pass input stage circuit, an action interference suppression stage circuit and a switch zeroing circuit;

[0007] The high-pass input stage circuit includes a floating electrode, a low bias current operational amplifier circuit A1, and an active low-pass feedback module;

[0008] The motion interference suppression stage circuit is an inverting integration circuit and includes an operational amplifier A3, a resistor R2, and a capacitor C2, and its output end is connected to the reference level pin REF of the low bias current operational amplifier circuit A1;

[0009] The switch clearing circuit includes a positive phase comparator A4, a negative phase comparator A5, a clearing switch S1 and a clearing switch S2;

[0010] The output end of the operational amplifier A3 is respectively connected to the non-inverting input end of the positive phase comparator A4 and the inverting input end of the inverting comparator A5; the output of the positive phase comparator A4 is connected to the control end of the zeroing switch S1, and the output end of the inverting comparator A5 is connected to the control end of the zeroing switch S2.

[0011] Furthermore, the active low-pass feedback module includes a low bias current operational amplifier A2, a resistor R1, and a capacitor C1, and the floating electrode is divided into two paths respectively connected to the non-inverting input terminal of the low bias current operational amplifier circuit A1 and the non-inverting input terminal of the low bias current operational amplifier A2.

[0012] Furthermore, the output end of the low bias current operational amplifier A2 is electrically connected to the inverting input end; one end of the resistor R1 is connected to the output end of the low bias current operational amplifier A2, and the other end is respectively connected to the inverting input end of the low bias current operational amplifier circuit A1 and the capacitor C1; the other end of the capacitor C1 is grounded.

[0013] Furthermore, the output end of the low bias current operational amplifier circuit A1 is connected to the inverting input end of the operational amplifier A3, and the resistor R2 is arranged on the connection line; one end of the capacitor C2 is connected to the inverting input end of the operational amplifier A3, and the other end is connected to the output end of the operational amplifier A3; the non-inverting input end of the operational amplifier A3 is grounded, and the output end is connected to the reference level pin REF of the low bias current operational amplifier circuit A1.

[0014] Furthermore, one end of the reset switch S1 and the reset switch S2 are both connected to the non-inverting input terminal of the low bias current operational amplifier circuit A1; the positive threshold voltage Vh+ is input to the inverting input terminal of the positive phase comparator A4; and the negative threshold voltage Vh- is input to the non-inverting input terminal of the inverting comparator A5.

[0015] Furthermore, the other ends of the reset switch S1 and the reset switch S2 are grounded.

[0016] Compared with the prior art, the beneficial effect of the automatic zeroing circuit of the suspended electrode for contactless ECG monitoring of the present invention is that when the output signal of the input stage of the measurement circuit is continuously saturated for a period of time, it can be automatically zeroed to ensure the continuation of ECG monitoring. The output signal is used to control the zeroing action of the suspended electrode, and it is necessary to distinguish the types of output signal exceeding the limit. The signal jitter caused by human body movement can be effectively identified to avoid unnecessary zeroing, and while suppressing the interference of human body movement, the continuous monitoring of ECG signals is guaranteed; for the case where the potential of the suspended electrode exceeds the common mode voltage range, this scheme can effectively identify and realize automatic and rapid zeroing to ensure the long-term stable operation of the circuit.

Brief Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of an embodiment of the present invention. [Specific implementation method]

[0018] Embodiment 1:

[0019] Please refer to Figure 1 This embodiment is a floating electrode automatic zeroing circuit 100 for contactless ECG monitoring, which includes a high-pass input stage circuit 1, a motion interference suppression stage circuit 2 and a switch zeroing circuit 3.

[0020] The high-pass input stage circuit 1 includes a floating electrode 11, a low bias current operational amplifier circuit A1, and an active low-pass feedback module. The active low-pass feedback module includes a low bias current operational amplifier A2, a resistor R1, and a capacitor C1. The floating electrode 11 is divided into two paths, which are respectively connected to the non-inverting input terminal of the low bias current operational amplifier circuit A1 and the non-inverting input terminal of the low bias current operational amplifier A2. The output terminal of the low bias current operational amplifier A2 is electrically connected to the inverting input terminal; one end of the resistor R1 is connected to the output terminal of the low bias current operational amplifier A2, and the other end is respectively connected to the inverting input terminal of the low bias current operational amplifier circuit A1 and the capacitor C1; the other end of the capacitor C1 is grounded. The output terminal of the active low-pass feedback module is formed between the resistor R1 and the capacitor C1, and is connected to the inverting input terminal of the low bias current operational amplifier circuit A1. The low bias current operational amplifier A2, the resistor R1 and the capacitor C1 form a low-pass filter, whose output enters the low bias current operational amplifier circuit A1, is subtracted from the ECG signal collected by the floating electrode 11, and is differentially amplified in the low bias current operational amplifier circuit A1, thereby achieving a high-pass effect. The typical value of the low-pass cut-off frequency is 0.1Hz to 1Hz.

[0021] The action interference suppression stage circuit 2 is an inverting integration circuit, and its output end is connected to the reference level pin REF of the low bias current operational amplifier circuit A1. The action interference suppression stage circuit 2 includes an operational amplifier A3, a resistor R2, and a capacitor C2. The output end of the low bias current operational amplifier circuit A1 is connected to the inverting input end of the operational amplifier A3, and the resistor R2 is arranged on the connection line; one end of the capacitor C2 is connected to the inverting input end of the operational amplifier A3, and the other end is connected to the output end of the operational amplifier A3; the same-direction input end of the operational amplifier A3 is grounded, and the output end is connected to the reference level pin REF of the low bias current operational amplifier circuit A1. The low bias current operational amplifier circuit A1 adopts a differential amplification structure, which mainly realizes two functions, one is to realize low bias current, and the other is to have a fixed gain of 10 times to 100 times. Multiple amplifiers can be used to form an instrument amplifier circuit structure, and a single-chip instrument amplifier can also be used to realize it. The bias current of the low bias current operational amplifier circuit A1 and the low bias current operational amplifier A2 is 10fA to 90fA.

[0022] The switch clearing circuit 3 includes a positive comparator A4, an inverting comparator A5, a clearing switch S1 and a clearing switch S2. The output end of the operational amplifier A3 in the inverting integration circuit is connected to the non-inverting input end of the positive comparator A4 and the inverting input end of the inverting comparator A5; the output of the positive comparator A4 is connected to the control end of the clearing switch S1, and the output of the inverting comparator A5 is connected to the control end of the clearing switch S2. One end of the clearing switch S1 and the clearing switch S2 are both connected to the non-inverting input end of the low bias current operational amplifier circuit A1; the positive threshold voltage Vh+ is input to the inverting input end of the positive comparator A4; the negative threshold voltage Vh- is input to the non-inverting input end of the inverting comparator A5. The other ends of the clearing switch S1 and the clearing switch S2 are grounded.

[0023] When the potential of the floating electrode 11 exceeds the positive upper limit of the common mode voltage of the low bias current operational amplifier circuit A1, the output of the low bias current operational amplifier circuit A1 continues to be positively saturated, and the capacitor C2 continues to integrate. When the output of the operational amplifier A3 is lower than the negative threshold voltage Vh-, the inverting comparator A5 output turns on the reset switch S2, and the floating electrode 11 is reset through the reset switch S2. The low bias current operational amplifier circuit A1 instantaneously outputs zero, the capacitor C2 discharges, the output of the operational amplifier A3 is higher than Vh-, the reset switch S2 is disconnected, the resetting of the floating electrode 11 is completed, and the monitoring of the electrocardiographic induction signal continues.

[0024] When the potential of the floating electrode 11 exceeds the negative upper limit of the common mode voltage of the low bias current operational amplifier circuit A1, the output of the low bias current operational amplifier circuit A1 continues to be negatively saturated, and the capacitor C2 continues to integrate. When the output of the operational amplifier A3 is higher than the positive threshold voltage Vh+, the positive comparator A4 output turns on the reset switch S1, and the floating electrode 11 is reset through the reset switch S1. The low bias current operational amplifier circuit A1 instantaneously outputs zero, the capacitor C2 discharges, the output of the operational amplifier A3 is lower than Vh+, the reset switch S1 is disconnected, the floating electrode 11 is reset, and the electrocardiographic induction signal continues to be monitored.

[0025] For abnormal jitter interference signals caused by human body movements, the jitter signals superimposed on the ECG signals will cause the output of the high-pass input stage circuit 1 to rise sharply in positive or negative phase, and the output voltage of the corresponding motion interference suppression stage circuit 2 will rise sharply in negative phase or positive phase. The output of the motion interference suppression stage circuit 2 is then fed back to the high-impedance amplifier A1 as a reference voltage, so that the output of the high-pass input stage circuit 1 tends to be stable, thereby suppressing the interference of the jitter signal caused by abnormal human body movements on the ECG signal; therefore, the potential of the floating electrode 11 will not exceed the common mode voltage range, and the jitter caused by human body movements will not trigger the zeroing action, thereby ensuring the effective and continuous ECG monitoring.

[0026] The present embodiment is a suspended electrode automatic zeroing circuit 100 for contactless ECG monitoring, which uses an output signal to control the zeroing action of the suspended electrode, and needs to distinguish the types of output signal exceeding the limit. Signal jitters generated by human body movements can be effectively identified to avoid unnecessary zeroing, and while suppressing human body movement interference, continuous monitoring of ECG signals is ensured; for situations where the potential of the suspended electrode exceeds the common mode voltage range, this solution can effectively identify and achieve automatic and rapid zeroing, ensuring long-term stable operation of the circuit.

[0027] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A floating electrode automatic zeroing circuit for non-contact ECG monitoring, characterized in that: It includes a high-pass input stage circuit, an action interference suppression stage circuit and a switch clearing circuit; The high-pass input stage circuit includes a floating electrode, a low bias current operational amplifier circuit A1, and an active low-pass feedback module; The motion interference suppression stage circuit is an inverting integration circuit and includes an operational amplifier A3, a resistor R2, and a capacitor C2, and its output end is connected to the reference level pin REF of the low bias current operational amplifier circuit A1; The switch clearing circuit includes a positive phase comparator A4, a negative phase comparator A5, a clearing switch S1 and a clearing switch S2; The output end of the operational amplifier A3 is connected to the non-inverting input end of the positive phase comparator A4 and the inverting input end of the inverting comparator A5 respectively; the output of the positive phase comparator A4 is connected to the control end of the zeroing switch S1, and the output end of the inverting comparator A5 is connected to the control end of the zeroing switch S2; The active low-pass feedback module includes a low bias current operational amplifier A2, a resistor R1, and a capacitor C1. The floating electrode is divided into two paths and connected to the non-inverting input terminal of the low bias current operational amplifier A1 and the non-inverting input terminal of the low bias current operational amplifier A2 respectively; the output terminal of the low bias current operational amplifier A2 is electrically connected to the inverting input terminal; one end of the resistor R1 is connected to the output terminal of the low bias current operational amplifier A2, and the other end is respectively connected to the inverting input terminal of the low bias current operational amplifier A1 and the capacitor C1; the other end of the capacitor C1 is grounded; the output terminal of the low bias current operational amplifier A1 is connected to the inverting input terminal of the operational amplifier A3, and the resistor R2 is arranged on the connection line; one end of the capacitor C2 is connected to the inverting input terminal of the operational amplifier A3, and the other end is connected to the output terminal of the operational amplifier A3; the non-inverting input terminal of the operational amplifier A3 is grounded, and the output terminal is connected to the reference level pin REF of the low bias current operational amplifier A1.

2. The automatic zeroing circuit of the floating electrode for non-contact ECG monitoring according to claim 1, characterized in that: One end of the reset switch S1 and the reset switch S2 are both connected to the non-inverting input terminal of the low bias current operational amplifier circuit A1; the inverting input terminal of the positive phase comparator A4 inputs the positive threshold voltage Vh+; the non-inverting input terminal of the inverting comparator A5 inputs the negative threshold voltage Vh-.

3. The automatic zeroing circuit of the floating electrode for contactless ECG monitoring according to claim 2, characterized in that: The other ends of the reset switch S1 and the reset switch S2 are grounded.

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