A wide frequency response electrocardio filter circuit

Abstract

The wide frequency response electrocardio filter circuit provided by the application sets an ESD static protection circuit, a first-stage signal low-pass circuit and a reverse voltage follower circuit through a signal stabilization module, prevents external static electricity from being introduced into the circuit through the ESD static protection circuit, stabilizes the signal through the first-stage signal low-pass circuit and the reverse voltage follower circuit, ensures that the subsequent circuit can process the voltage and frequency response range of the stable signal, and improves the practicability of the equipment.

Description

Technical Field

[0001] This utility model relates to the field of medical device technology, specifically to a wide-frequency response electrocardiogram filter circuit. Background Technology

[0002] Frequency response range refers to the frequency range of ECG signals that a device can effectively capture. Common portable Holter monitors typically have a frequency response range of 0.67~40Hz, which is sufficient for routine diagnostic needs and most patients. However, for some patients with specific conditions, this range is insufficient, and the acquired ECG signals cannot help doctors make accurate judgments. For example, in ECG signals related to ST segment depression and ventricular late potentials (VLPs), ST segment depression requires a lower frequency (0.05Hz) to ensure the complete preservation of the ST segment depression, while VLPs require a higher frequency (300Hz) to ensure more details of the ECG wave are preserved. Clearly, if a patient needs to be diagnosed with ST segment depression or VLPs, the circuit's frequency response range needs to be sufficiently wide. Furthermore, because common portable Holter monitors are carried around, static electricity generated during activity or electromagnetic interference from mobile phones can lead to signal instability, especially in the dry autumn and winter months in northern regions, which can easily cause abnormal data acquisition. These issues limit the application scenarios of portable dynamic electrocardiogram recorders. Summary of the Invention

[0003] To address the issues of common portable dynamic electrocardiogram (ECG) recorders' inability to capture ECG signals for certain specific diseases due to their limited frequency response range, as well as signal instability, this invention provides a wide-frequency-response ECG filtering circuit. This circuit can more stably capture ECG signals over a wider frequency response range, enabling the device to be applied in more scenarios.

[0004] The structure of this utility model is as follows: a wide frequency response electrocardiogram filter circuit, characterized in that it includes: a signal stabilization module, a preamplifier circuit, a high-pass filter circuit, and a main amplifier circuit; The signal stabilization module includes: an ESD electrostatic protection circuit, a first-stage low-pass circuit, and an inverted voltage follower circuit arranged sequentially; the signal stabilization module is located between the signal input terminal and the preamplifier circuit; the preamplifier circuit is based on an instrumentation amplifier, which amplifies the two input signals and then sends the signals to the high-pass filter circuit; the output terminal of the high-pass filter circuit is connected to the main amplifier circuit. The main amplification circuit includes a two-stage amplification circuit and a two-stage low-pass filter circuit. The two-stage amplification circuit is based on an operational amplifier. After the signal is amplified by the two-stage amplification circuit, it is filtered by the two-stage low-pass filter circuit and then output as a signal that meets the target frequency response range.

[0005] Its further features are: The signal stabilization module includes: diodes D1 and D2, capacitors C201 and C203, resistors R200~R205, and operational amplifier A200; The positive terminal of diode D1 is connected to AVSS, the negative terminal of diode D1 is connected to the signal input terminal of the first electrode plate and one end of resistor R200, the other end of resistor R200 is connected to one end of capacitor C201, one end of resistor R201, and pin 3 of operational amplifier 200, the other end of capacitor C201 is connected to one end of resistor R202 and then connected to digital ground, the other end of resistor R202 is connected to the other end of resistor R201, pin 13 of operational amplifier A200 is connected to AVSS1, pin 4 of operational amplifier A200 is connected to AVDD1, and pin 2 of operational amplifier A200 is connected to pin 1 of operational amplifier A200 and then connected to the first-stage amplification module; The anode of diode D2 is connected to AVSS, and the cathode of diode D2 is connected to the signal input terminal of the second electrode and one end of resistor R203. The other end of resistor R203 is connected to one end of capacitor C203, one end of resistor R204, and pin 5 of operational amplifier A200. The other end of capacitor C203 is connected to one end of resistor R205 and then to digital ground. The other end of resistor R205 is connected to the other end of resistor R204. Pin 6 of operational amplifier A200 is connected to pin 7 of operational amplifier A200 and then to the first-stage amplification module. The preamplifier circuit includes: instrumentation amplifier A121, resistors R121, R122, and R123; the high-pass filter circuit includes: capacitor C121 and resistor R124. Pin 2 of instrumentation amplifier A121 is connected to pin 1 of operational amplifier A200 via resistor R121. Pin 3 of instrumentation amplifier A121 is connected to pin 7 of operational amplifier A200 via resistor R122. Pin 4 of instrumentation amplifier A121 is connected to AVSS. Pin 7 of instrumentation amplifier A121 is connected to AVDD1. Pin 5 of instrumentation amplifier A121 is connected to one end of resistor R124 and then connected to digital ground. Pin 1 of instrumentation amplifier A121 is connected to one end of resistor R123. The other end of resistor R123 is connected to pin 8 of instrumentation amplifier A121. Pin 6 of instrumentation amplifier A121 is connected to one end of capacitor C121. The other end of capacitor C121 is connected to the other end of resistor R124 and then serves as the output of the high-pass filter circuit, which is connected to the main amplifier circuit. The main amplifier circuit includes: operational amplifier A122, capacitor C122, resistor R126 and resistor R127; Pin 3 of the operational amplifier A122 is connected to the input of the high-pass filter circuit. Pin 2 of the operational amplifier A122 is connected to one end of the capacitor C122, one end of the resistor R126, and one end of the resistor R127. Pin 8 of the operational amplifier A122 is connected to AVDD. The other end of the resistor R127 is connected to digital ground. The other end of the capacitor C122 is connected to the other end of the resistor R126 and then connected to pin 1 of the operational amplifier A122 as the signal output terminal of the main amplifier circuit. It also includes: a level conversion circuit, which includes: resistors R128 and R129; The output signal of the main amplifier circuit is fed into one end of the resistor R128. The other end of the resistor R128 is connected to pin 6 of the operational amplifier A122 and one end of the resistor R129. Pin 5 of the operational amplifier A122 is connected to AVEE. The other end of the resistor R129 is connected to pin 7 of the operational amplifier A122 and serves as the signal output terminal of the level conversion circuit. The instrumentation amplifier A121 is based on the INA333 instrumentation amplifier; the operational amplifier is based on the OPA2336E operational amplifier. The high-pass filter circuit and the main amplifier circuit are connected by the resistor R125; The capacitance of capacitor C121 in the high-pass filter circuit is 10 × 10 5 The resistor R126 in the main amplifier circuit is 24.9KΩ, and the capacitor C122 is 20 × 10⁻⁶ kΩ. 3 PF; In the high-pass filter circuit, resistor R123 is 24.9 kΩ; in the main amplifier circuit, resistor R126 is 24.9 kΩ and resistor R127 is 499 Ω.

[0006] This application provides a wide-frequency response ECG filtering circuit. It incorporates an ESD electrostatic protection circuit, a first-stage low-pass circuit, and an inverted voltage follower circuit through a signal stabilization module. The ESD electrostatic protection circuit prevents external static electricity from entering the circuit. The first-stage low-pass circuit and the inverted voltage follower circuit stabilize the signal, ensuring that subsequent circuits can process the voltage and frequency response range based on the stabilized signal, thus improving the practicality of the device. This application uses an instrumentation amplifier A121 in the preamplifier circuit to amplify the difference between voltage signals from two different electrode inputs, then sends it to a high-pass filter circuit for high-pass filtering. By controlling the values ​​of capacitor C121 and resistor R124, the cutoff frequency meets the requirement of 0.05Hz. This application also includes a second-stage amplifier... The main amplifier circuit and the secondary low-pass filter circuit are designed as a single unit. The amplifier circuit is formed by operational amplifier A122, resistors R126 and R127. The secondary amplification factor is adjusted by controlling the resistance values ​​of resistors R126 and R127. At the same time, the low-pass filter circuit is formed by resistor R126 and capacitor C122. By controlling the values ​​of resistor R126 and capacitor C122, the cutoff frequency meets the requirement of 300Hz. In this application, the secondary low-pass filter circuit and the secondary amplifier module are integrated together to achieve more functions with fewer components. It can amplify the voltage signal of the signal input from the two electrode plates and also amplify the signal frequency response range to 0.05Hz~300Hz, making the circuit more suitable for portable dynamic electrocardiogram recorder devices. Attached Figure Description

[0007] Figure 1 This is a structural diagram of the wide-frequency response ECG filter circuit of this application. Detailed Implementation

[0008] like Figure 1 As shown, this application discloses a wide-frequency response electrocardiogram (ECG) filter circuit, which includes: a signal stabilization module, a preamplifier circuit, a high-pass filter circuit, a main amplifier circuit, and a level conversion circuit.

[0009] This application supports two signal input terminals. The ECG signal is sent to the signal stabilization module via electrode pads LL and RA. The signal stabilization module includes, for each of the two signal input terminals, a sequentially connected ESD electrostatic protection circuit, a first-stage low-pass circuit, and an inverted voltage follower circuit. The signal stabilization module is positioned between the two signal input terminals and the preamplifier circuit. The preamplifier circuit, based on an instrumentation amplifier, amplifies the two signals and then sends them to a high-pass filter circuit. The output of the high-pass filter circuit is connected to the main amplifier circuit. The main amplifier circuit includes a second-stage amplifier circuit and a second-stage low-pass filter circuit. The second-stage amplifier circuit, based on an operational amplifier, amplifies the signal and then filters it before outputting a signal that conforms to the target frequency response range.

[0010] The signal stabilization module includes: diodes D1 and D2, capacitors C201 and C203, resistors R200~R205 and operational amplifier A200. D1 and D2 are based on diodes of model ESD5Z3.3T1.

[0011] The positive terminal of diode D1 is connected to AVSS, and the negative terminal of diode D1 is connected to the signal input terminal of the LA electrode and one end of resistor R200. The other end of resistor R200 is connected to one end of capacitor C201, one end of resistor R201, and pin 3 of operational amplifier A200. The other end of capacitor C201 is connected to one end of resistor R202 and then to digital ground. The other end of resistor R202 is connected to the other end of resistor R201. Pin 13 of operational amplifier A200 is connected to AVSS1, pin 4 of operational amplifier A200 is connected to AVDD1, and pin 2 of operational amplifier A200 is connected to pin 1 of operational amplifier A200 and then to the first-stage amplification module.

[0012] The positive terminal of diode D2 is connected to AVSS, and the negative terminal of diode D2 is connected to the signal input terminal of the RA electrode and one end of resistor R203. The other end of resistor R203 is connected to one end of capacitor C203, one end of resistor R204, and pin 5 of operational amplifier A200. The other end of capacitor C203 is connected to one end of resistor R205 and then to digital ground. The other end of resistor R205 is connected to the other end of resistor R204. Pin 6 of operational amplifier A200 is connected to pin 7 of operational amplifier A200 and then connected to a first-stage amplification module.

[0013] In the signal stabilization module, the SD electrostatic protection circuit: signals LA and RA are protected against ±30K ESD by two ESD protection diodes, D1 and D2. An active low-pass filter, composed of resistor R200 (10KΩ) and capacitor C201 (2200pF), serves as the first-stage signal low-pass circuit, performing preliminary screening of the signals input from the two LA and RA stage chips to eliminate abnormal signals. The cutoff frequency F0 of the first-stage signal low-pass circuit is calculated as follows: F0=1 / (2*PI*R200*C201)=1 / (2*3.14*10*10^3*2200*10^-12)=7237HZ.

[0014] The signal stabilization module uses a low-voltage, low-power (20μA / op-amp), full-amplitude output quad operational amplifier OPA4336E to form an inverting voltage follower circuit to drive all input signals, making the input signals more stable. Input impedance: >10MΩ. Independent capacitor decoupling filter circuits are used between each stage, while a common capacitor decoupling filter circuit is used within each stage.

[0015] The preamplifier circuit includes: instrumentation amplifier A121, resistors R121, R122 and R123; the high-pass filter circuit includes: capacitor C121 and resistor R124; the instrumentation amplifier A121 is based on the INA333 instrumentation amplifier. Pin 2 of instrumentation amplifier A121 is connected to pin 1 of A200 via resistor R121, providing one signal input; pin 3 of instrumentation amplifier A121 is connected to pin 7 of A200 via resistor R122, providing another signal input; pin 4 of instrumentation amplifier A121 is connected to AVSS; pin 7 of instrumentation amplifier A121 is connected to AVDD1; pin 5 of instrumentation amplifier A121 is connected to one end of resistor R124 and then connected to digital ground; pin 1 of instrumentation amplifier A121 is connected to one end of resistor R123; the other end of resistor R123 is connected to pin 8 of instrumentation amplifier A121; pin 6 of instrumentation amplifier A121 is connected to one end of capacitor C121; the other end of capacitor C121 is connected to the other end of resistor R124 and then used as the output of the high-pass filter circuit, which is then connected to the main amplifier circuit.

[0016] The main tasks of the preamplifier circuit are impedance matching and common-mode interference suppression. The operational amplifier is required to have low noise and a high common-mode rejection ratio (CMRR). In this embodiment, the INA333 instrumentation amplifier, characterized by low voltage, low noise, low power consumption (50μA), and full-amplitude output, is selected.

[0017] Input filtering: After the input signal is filtered by the first-stage low-pass circuit in the signal stabilization module, the input impedance can be improved, enhancing the circuit's anti-interference capability and signal integrity. In the preamplifier circuit, a 10KΩ resistor (R121 and R122) is connected in series with each of the two input terminals to balance the electrode-skin contact resistance, thereby improving the CMRR in actual use.

[0018] The gain G1 of the preamplifier circuit: G1 = 1 + (100kΩ / R) 123 =1 + [100 kΩ / (24.9 kΩ)] = 5, meaning the input signal is amplified by 5 times. CMRR: The CMRR of the INA333 reaches over 100dB.

[0019] This application incorporates a high-pass filter circuit after the preamplifier circuit. Using RC coupling (R124=3.92MΩ, C121=1μF), the high-pass filter circuit not only expands the frequency response range of the ECG signal but also blocks low-frequency electrode polarization voltages, improving signal stability. The filter cutoff frequency F1 is: F1=1 / (2*PI*R124*C121)=1 / (2*3.14*3.92*10^6*10*10^5*10^-12)=0.0406Hz.

[0020] The high-pass filter circuit and the main amplifier circuit are connected by a resistor R125.

[0021] The main amplifier circuit includes: operational amplifier A122, capacitor C122, resistors R126 and R127. The operational amplifier is based on the OPA2336E model. Pin 3 of operational amplifier A122 is connected to the input of the high-pass filter circuit. Pin 2 of operational amplifier A122 is connected to one end of capacitor C122, one end of resistor R126, and one end of resistor R127. Pin 8 of operational amplifier A122 is connected to AVDD. The other end of resistor R127 is connected to digital ground. The other end of capacitor C122 is connected to the other end of resistor R126 and then to pin 1 of operational amplifier A122 as the signal output terminal of the main amplifier circuit. In the main amplifier circuit, resistor R126 is 24.9KΩ, and capacitor C122 is 20 × 10⁻⁶Ω. 3 PF; In the main amplifier circuit, resistor R126 is 24.9 kΩ and resistor R127 is 499 Ω.

[0022] The main amplifier circuit includes a two-stage amplifier circuit and a two-stage low-pass filter circuit; its main tasks are amplification and low-pass filtering, and the output of the main amplifier circuit is the ECG signal. A dual operational amplifier OPA2336E is selected. The gain G2 of the two-stage amplifier circuit is: G2 = 1 + [R126 / R127] = 50 times.

[0023] In this application, after passing through the preamplifier circuit and the secondary amplifier circuit, the total amplification factor is G1*G2=5*50=250.

[0024] In the two-stage low-pass filter circuit, a feedback resistor R126 (33KΩ) and a feedback capacitor C122 (0.1μ) are connected in parallel to form an active low-pass filter, making the high-side cutoff frequency of the amplifier 48Hz (-3dB). The cutoff frequency F2 is calculated as follows: F2=1 / (2*PI*R126*C122)=1 / (2*3.14*24.9*10^3*20*10^3*10^-12)=318Hz.

[0025] After processing by a high-pass filter circuit and a two-stage low-pass filter circuit, the technical solution of this application adjusts the frequency response range of the existing dynamic electrocardiogram recorder from 0.67~40Hz to 0.0406Hz~318Hz, making it applicable to more application scenarios.

[0026] Since the gain of the preamplifier circuit is relatively small, the noise of the secondary amplifier circuit cannot be ignored. Because the OPA2336E has low noise and meets the requirements of the registration standard, the OPA2336E is selected to amplify the signal in the secondary amplifier circuit.

[0027] This application also utilizes operational amplifier A122 to construct a level conversion circuit, which converts the signal level output from pin 1 of operational amplifier A122 to ensure applicability to more scenarios. The level conversion circuit includes resistors R128 and R129. The output signal of the main amplifier circuit is fed into one end of resistor R128, and the other end of resistor R128 is connected to pin 6 of operational amplifier A122 and one end of resistor R129. Pin 5 of operational amplifier A122 is connected to AVEE, and the other end of resistor R129 is connected to pin 7 of operational amplifier A122, serving as the signal output terminal of the level conversion circuit.

[0028] In this application, the digital ground and the center level (circuit reference potential) of the battery share the same reference point. The battery voltage is 3.3V, therefore the battery center level is 1.65V. The output of the preamplifier circuit is 0-3.3V, with a center level of 1.65V. However, in this embodiment, the input of the MCU's ADC transistor is 0-2.5V, with a center level of 1.25V. Therefore, level conversion is necessary. A 1x gain op-amp circuit is used for level conversion. The level conversion formula is: AVE1 = (2.5V / 2 - 3.3V / 2) / 2 + 3.3V / 2 = 1.45V.

[0029] In this application, the power supply and ground lines in all preamplifier circuits and secondary amplifier circuits share an independent capacitor decoupling filter circuit. That is, in the preamplifier circuit, AVDD1 is connected to AVSS1 through capacitor C123; in the secondary amplifier circuit, AVDD1 is connected to AVSS1 through capacitor C124. The advantage of doing this is that it can filter out high-frequency or low-frequency interference.

[0030] After using the technical solution of this utility model, the voltage difference of the human body is amplified in one stage by the instrumentation operational amplifier, a high-pass filter is formed by capacitors and resistors, a low-pass amplifier circuit is formed by the operational amplifier circuit and resistors and capacitors, and then the signal is converted by the level conversion circuit before finally entering the MCU ADC for sampling and analysis.

Claims

1. A wide-frequency response electrocardiogram (ECG) filter circuit, characterized in that, It includes: Signal stabilization module, preamplifier circuit, high-pass filter circuit, and main amplifier circuit; The signal stabilization module includes: an ESD electrostatic protection circuit, a first-stage low-pass circuit, and an inverted voltage follower circuit arranged sequentially; the signal stabilization module is located between the signal input terminal and the preamplifier circuit; the preamplifier circuit is based on an instrumentation amplifier, which amplifies the two input signals and then sends the signals to the high-pass filter circuit; the output terminal of the high-pass filter circuit is connected to the main amplifier circuit. The main amplification circuit includes a two-stage amplification circuit and a two-stage low-pass filter circuit. The two-stage amplification circuit is based on an operational amplifier. After the signal is amplified by the two-stage amplification circuit, it is filtered by the two-stage low-pass filter circuit and then output as a signal that meets the target frequency response range.

2. The wide-frequency response ECG filter circuit according to claim 1, characterized in that: The signal stabilization module includes: diodes D1 and D2, capacitors C201 and C203, resistors R200~R205, and operational amplifier A200; The positive terminal of diode D1 is connected to AVSS, the negative terminal of diode D1 is connected to the signal input terminal of the first electrode plate and one end of resistor R200, the other end of resistor R200 is connected to one end of capacitor C201, one end of resistor R201, and pin 3 of operational amplifier 200, the other end of capacitor C201 is connected to one end of resistor R202 and then connected to digital ground, the other end of resistor R202 is connected to the other end of resistor R201, pin 13 of operational amplifier A200 is connected to AVSS1, pin 4 of operational amplifier A200 is connected to AVDD1, and pin 2 of operational amplifier A200 is connected to pin 1 of operational amplifier A200 and then connected to the first-stage amplification module; The positive terminal of diode D2 is connected to AVSS, and the negative terminal of diode D2 is connected to the signal input terminal of the second electrode plate and one end of resistor R203. The other end of resistor R203 is connected to one end of capacitor C203, one end of resistor R204, and pin 5 of operational amplifier A200. The other end of capacitor C203 is connected to one end of resistor R205 and then to digital ground. The other end of resistor R205 is connected to the other end of resistor R204. Pin 6 of operational amplifier A200 is connected to pin 7 of operational amplifier A200 and then to the first-stage amplification module.

3. The wide-frequency response ECG filter circuit according to claim 2, characterized in that: The preamplifier circuit includes: instrumentation amplifier A121, resistors R121, R122, and R123; the high-pass filter circuit includes: capacitor C121 and resistor R124. Pin 2 of instrumentation amplifier A121 is connected to pin 1 of operational amplifier A200 via resistor R121. Pin 3 of instrumentation amplifier A121 is connected to pin 7 of operational amplifier A200 via resistor R122. Pin 4 of instrumentation amplifier A121 is connected to AVSS. Pin 7 of instrumentation amplifier A121 is connected to AVDD1. Pin 5 of instrumentation amplifier A121 is connected to one end of resistor R124 and then connected to digital ground. Pin 1 of instrumentation amplifier A121 is connected to one end of resistor R123. The other end of resistor R123 is connected to pin 8 of instrumentation amplifier A121. Pin 6 of instrumentation amplifier A121 is connected to one end of capacitor C121. The other end of capacitor C121 is connected to the other end of resistor R124 and then serves as the output of the high-pass filter circuit, which is connected to the main amplifier circuit. The main amplifier circuit includes: operational amplifier A122, capacitor C122, resistor R126 and resistor R127; Pin 3 of the operational amplifier A122 is connected to the input of the high-pass filter circuit. Pin 2 of the operational amplifier A122 is connected to one end of the capacitor C122, one end of the resistor R126, and one end of the resistor R127. Pin 8 of the operational amplifier A122 is connected to AVDD. The other end of the resistor R127 is connected to digital ground. The other end of the capacitor C122 is connected to the other end of the resistor R126 and then connected to pin 1 of the operational amplifier A122 as the signal output terminal of the main amplifier circuit.

4. The wide-frequency response ECG filter circuit according to claim 3, characterized in that: It also includes: a level conversion circuit, which includes: resistors R128 and R129; The output signal of the main amplifier circuit is fed into one end of the resistor R128. The other end of the resistor R128 is connected to pin 6 of the operational amplifier A122 and one end of the resistor R129. Pin 5 of the operational amplifier A122 is connected to AVEE. The other end of the resistor R129 is connected to pin 7 of the operational amplifier A122 and serves as the signal output terminal of the level conversion circuit.

5. The wide-frequency response ECG filter circuit according to claim 1, characterized in that: The instrumentation amplifier A121 is based on the INA333 instrumentation amplifier; the operational amplifier is based on the OPA2336E operational amplifier.

6. The wideband response ECG filter circuit according to claim 1, characterized in that: The high-pass filter circuit and the main amplifier circuit are connected by the resistor R125.

7. The wide-frequency response ECG filter circuit according to claim 3, characterized in that: The capacitance of capacitor C121 in the high-pass filter circuit is 10 × 10 5 The resistor R126 in the main amplifier circuit is 24.9KΩ, and the capacitor C122 is 20 × 10⁻⁶ kΩ. 3 PF.

8. The wide-frequency response ECG filter circuit according to claim 3, characterized in that: In the high-pass filter circuit, resistor R123 is 24.9 kΩ; in the main amplifier circuit, resistor R126 is 24.9 kΩ and resistor R127 is 499 Ω.

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