Skin impedance detection circuit and radio frequency treatment equipment

Abstract

The invention relates to a skin impedance detection circuit and radio frequency treatment equipment, and the circuit comprises a detection electrode module which is used for making contact with human skin to form a current detection loop; the differential current acquisition circuit is connected in series in the current detection loop and is configured to convert the excitation current flowing through the detection electrode module into a differential voltage signal; the amplifying circuit capable of digitally controlling gain is connected to the output end of the differential current acquisition circuit and is configured to receive the differential voltage signal, switch gain gears according to a digital control signal and output an amplified analog signal; and the main control module is connected to the amplifying circuit capable of digitally controlling the gain, and is configured to collect the amplified analog signal, calculate a skin impedance value by combining the current gain gear and the known excitation parameter, and generate an equipment control instruction according to the skin impedance value. The skin impedance detection circuit can detect impedance in real time and set a safety threshold value, and when the impedance exceeds a normal range, the equipment can immediately pause output or reduce power.

Description

Technical Field

[0001] This invention relates to the field of radiofrequency therapy technology, and more specifically, to a radiofrequency therapy device. Background Technology

[0002] Radiofrequency (RF) therapy devices utilize radiofrequency energy to act on the skin and subcutaneous tissue, thereby generating a thermal effect. Chinese Patent CN221750753U discloses an RF therapy handpiece and an RF therapy device. The RF therapy handpiece includes an RF therapy head, a housing, and a first circuit board. The RF therapy head is designed for contact with the skin to perform RF therapy. The housing has the RF therapy head and an external power supply device at its two ends, respectively. The first circuit board is located inside the housing, extending axially along the housing, and its two ends are electrically connected to the RF therapy head and the external power supply device, respectively. This solution discloses the basic components of an RF therapy device and details the configuration of the relevant circuit board.

[0003] During radiofrequency ablation, skin contact impedance is a key variable in energy transfer and is directly related to safety risks. If poor skin contact occurs (e.g., air gaps, sweat, or dirt between the electrode and skin), the contact impedance will increase sharply. In this case, the radiofrequency energy cannot effectively penetrate to the target subcutaneous tissue and will instead concentrate on the skin surface, causing a sudden rise in local temperature and potentially leading to epidermal burns, blistering, and other injuries. Summary of the Invention

[0004] The purpose of this invention is to provide a skin impedance detection circuit and a radiofrequency treatment device to solve the problems existing in the prior art.

[0005] The objective of this invention is achieved as follows: a skin impedance detection circuit, applied in a radiofrequency therapy device, comprising:

[0006] The detection electrode module is used to form a current detection circuit by contacting human skin.

[0007] A differential current acquisition circuit, connected in series in the current detection loop, is configured to convert the excitation current flowing through the detection electrode module into a differential voltage signal;

[0008] A digitally gain-controlled amplifier circuit is connected to the output of the differential current acquisition circuit, configured to receive the differential voltage signal and switch the gain level according to the digital control signal, outputting an amplified analog signal; and

[0009] The main control module is connected to the digitally controllable gain amplifier circuit and is configured to acquire the amplified analog signal, calculate the skin impedance value by combining the current gain level and known excitation parameters, and generate device control commands based on the skin impedance value.

[0010] Furthermore, the differential current acquisition circuit includes:

[0011] A sampling resistor is connected in series in the current detection circuit, and a differential voltage is generated across the sampling resistor when the excitation current flows through it.

[0012] A filtering unit is connected between the two ends of the sampling resistor and the input terminal of the digitally controllable gain amplifier circuit to filter out high-frequency interference signals.

[0013] Furthermore, the filtering unit is an RC low-pass filter, including resistors connected in series between the two ends of the sampling resistor and the input terminal of the amplifier circuit, and a capacitor connected across the two input terminals of the amplifier circuit.

[0014] Furthermore, the digitally controllable gain amplifier circuit includes:

[0015] An instrumentation amplifier has a first input terminal, a second input terminal, an output terminal, a reference voltage terminal, and a gain setting terminal;

[0016] A variable resistor network, connected to the gain setting terminal, is used to set the amplification factor of the instrumentation amplifier;

[0017] An electronic switch, controlled by the digital control signal, is configured to be turned on or off to change the equivalent resistance of the variable resistor network;

[0018] When the electronic switch is in the off state, the variable resistor network exhibits a first resistance value, corresponding to a first gain level; when the electronic switch is in the on state, the variable resistor network exhibits a second resistance value, corresponding to a second gain level; the first resistance value is greater than the second resistance value, making the first gain level less than the second gain level.

[0019] Furthermore, the variable resistor network includes:

[0020] A basic resistor branch contains at least one basic resistor;

[0021] An additional resistor branch, which includes at least one additional resistor;

[0022] The additional resistor branch and the basic resistor branch are connected in series between the gain setting terminals;

[0023] The electronic switch is connected in parallel with the additional resistor branch;

[0024] When the electronic switch is turned off, the additional resistor branch is connected to the circuit, and the equivalent resistance of the variable resistor network is the sum of the resistance values ​​of the basic resistor branch and the additional resistor branch.

[0025] When the electronic switch is turned on, the additional resistor branch is short-circuited by the electronic switch, and the equivalent resistance of the variable resistor network is the resistance of the basic resistor branch.

[0026] Furthermore, the electronic switch is an optocoupler, the output terminal of which includes a MOSFET, the drain and source of which are connected in parallel across the additional resistor branch, and the input terminal of the optocoupler receives the digital control signal.

[0027] Furthermore, the digitally controllable gain amplifier circuit also includes a DC bias unit, which is connected to the reference voltage terminal of the instrumentation amplifier to provide a stable DC reference level so that the output signal is superimposed on a preset DC bias voltage.

[0028] Furthermore, the main control module is configured to execute the following security control logic:

[0029] The calculated skin impedance value is compared with a preset safety threshold range;

[0030] If the skin impedance value exceeds the safety threshold range, a control command is generated to reduce the radio frequency output power or stop the radio frequency output.

[0031] If the skin impedance value is within the safe threshold range, the current operating state is maintained or power increase is allowed.

[0032] Furthermore, the excitation current is a radio frequency alternating current, the frequency of which is consistent with the operating frequency of the radio frequency therapy device or is a specific detection frequency.

[0033] As another aspect of the present invention, a radiofrequency therapy device is provided, comprising a radiofrequency energy generation module and the skin impedance detection circuit described above.

[0034] The radio frequency energy generation module is configured to provide excitation current to the detection electrode module;

[0035] The device control commands generated by the main control module of the skin impedance detection circuit are connected to the control terminal of the radio frequency energy generation module to adjust the output of radio frequency energy.

[0036] The beneficial effects of this invention are as follows:

[0037] 1. The number of core components is relatively small. The entire signal path consists of an instrumentation amplifier, a small number of external resistors and capacitors, and a relay. There are no complex multi-stage amplification, filtering, or modulation / demodulation circuits.

[0038] 2. The control logic is simple; gain fine-tuning can be achieved by controlling a relay with just a digital signal, without the need for complex programming or digital potentiometers. The instrumentation amplifier naturally possesses a high common-mode rejection ratio, effectively suppressing 50Hz / 60Hz power frequency interference and other common-mode noise carried by the human body. This is crucial for extracting weak bioelectrical signals from the human body surface (whose impedance changes modulate the signal).

[0039] 3. The load effect on the human body being measured is minimal, avoiding the problem of inaccurate impedance measurement caused by factors of the measuring equipment itself. By extracting the voltage difference across the skin through a dedicated differential amplifier, common-mode interference (such as environmental electromagnetic noise and electrode contact noise) can be effectively suppressed. Compared with traditional mechanical switches or ordinary analog switches, its on-resistance is small and its switching noise is low, avoiding signal distortion and significantly improving the accuracy of impedance measurement.

[0040] 4. Simultaneously, without altering the core architecture, signal attenuation caused by differences in sensor (electrode) contact with the skin can be compensated by switching the gain. It can automatically switch the amplification factor based on skin impedance, using low gain at low impedance to avoid signal saturation and high gain at high impedance to ensure measurability, thus solving the problem of "either inaccurate measurement or no measurement at all" in existing technologies. Attached Figure Description

[0041] Figure 1 This is a circuit diagram of a high-precision instrument amplifier with digitally controllable gain, as described in this invention.

[0042] Figure 2 This is the differential current acquisition circuit diagram of the present invention. Detailed Implementation

[0043] The following will refer to the appendices in the embodiments of the present invention. Figure 1-2 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] like Figure 1-2 As shown, a skin contact impedance detection circuit is proposed to address the problems arising in existing technologies. By adding this circuit to a radiofrequency therapy device, impedance can be detected in real time and a safety threshold can be set. When the impedance exceeds the normal range (too high or too low), the device can immediately pause output or reduce power.

[0045] The skin impedance detection circuit consists of three modules: a differential current acquisition circuit (part one), a high-precision instrumentation amplifier circuit with digitally controllable gain (part two), and an MCU. In the circuit, NT+ and NT- are the detection electrodes, which need to be in direct contact with the skin to form a current loop. When the excitation current flows through the skin, a voltage difference V_skin will be generated between NT+ and NT- due to the skin impedance.

[0046] like Figure 2 As shown, the first part is a differential current acquisition scheme based on a shunt resistor, which adopts a design of "current-to-voltage conversion + differential filtering". The current to be measured flows through R187 (0.1Ω), generating a differential voltage V_skin=I×R187 across it; R188 and R189 limit the current and match the impedance of the differential voltage, and together with C148 form a differential RC low-pass filter to filter out high-frequency interference signals; the processed differential voltage is output from MI+ and MI-, and enters the amplifier for analog-to-digital conversion or amplification, ultimately achieving accurate current measurement.

[0047] like Figure 1 As shown, the second part utilizes the AD8421ARMZ high-precision instrumentation amplifier, characterized by low noise and high common-mode rejection ratio. Its design features are perfectly suited to the high-precision requirements of skin detection scenarios. In skin detection, the signals acquired by the electrodes are typically in the microvolt range (μV), such as voltage fluctuations caused by changes in skin impedance (typically ranging from 10μV to 1mV) or bioelectrical signals (such as mV-level signals from ECG). The AD8421ARMZ amplifies the differential input signals (MI+ / MI-) and outputs MI_OUT, which is used to switch the resistor network to change the amplifier gain.

[0048] The second part of the circuit implementation: The operational amplifier amplifies the differential input signal and outputs MI_OUT to the MCU, while referencing +1.5VREF (used to set the DC bias or reference level).

[0049] When K3 is off (MJ_GAIN_SEL is invalid, optocoupler is not conducting), the MOSFET inside the optocoupler is off, R199 is in the pass state, and the current flows through R200 (9.31kΩ), R198 (100Ω), and R199 (487Ω) connected in series to form a gain resistor network. The total resistance is relatively large. The calculation formula is G=1+9.9kΩ / RG, RG=R200+R198+R199=9.897kΩ, so the gain is about 2 times (gain is inversely proportional to resistance, the larger the resistance, the smaller the gain).

[0050] When K3 is closed (MJ_GAIN_SEL is active, optocoupler is on), the MOSFET inside the optocoupler is on, and the current flows directly through R199. At this time, the calculation formula is G=1+9.9kΩ / RG, RG=R199=487Ω, so the gain is about 20 times (the smaller the resistance, the greater the gain).

[0051] The ±15V power supply provides the operating voltage for the instrumentation amplifier. Filter capacitors C150, C151, C152, and C153 filter out power supply noise, ensuring the stability and accuracy of the amplifier circuit. R201 and R202 limit the power supply current to prevent overcurrent damage to the chips. +1.5VREF provides the DC reference level for the instrumentation amplifier, used to set the DC bias of the output signal. C153 is a decoupling capacitor that filters high-frequency noise on +1.5VREF, ensuring the stability of the reference voltage. A stable reference level prevents noise from being introduced into the output signal, ensuring amplification accuracy. In summary, this circuit, by providing a stable DC reference voltage, achieves both DC bias control of the output signal and suppresses noise interference from the reference voltage, making it a crucial element in ensuring the amplifier's output characteristics.

[0052] The above technical solution can be summarized as follows: This skin impedance detection circuit works collaboratively through three core components: excitation signal application, impedance signal acquisition, and high-precision amplification and gain adaptation. The differential current acquisition circuit (R187, R188, R189, C148) is used to generate or condition the excitation signal applied to the skin (such as a small-amplitude AC current / voltage). Skin impedance is a resistive load. By applying an excitation signal with known characteristics to the skin, the excitation current is provided by the front-end circuit (such as a constant current source). When flowing through the skin, the skin impedance generates a voltage difference V_skin between NT+ and NT-, which is input as a differential signal through MI+ / MI- to the high-precision instrumentation amplifier U11 (AD8421ARMZ), and U11 achieves ×2 / ×20 gain switching. The amplified skin voltage signal is output through NT_OUT and enters the MCU's ADC sampling pin. Impedance inversion: The MCU performs calculations on the digital quantity sampled by the ADC, combining the known excitation current I and the amplifier circuit parameters. The corresponding calculation formula is: Z_skin = V_skin × gain / I.

[0053] The advantages of the above scheme are as follows:

[0054] 4. The number of core components is relatively small. The entire signal path consists of an instrumentation amplifier (AD8421ARMZ), a small number of external resistors and capacitors, and a relay. There are no complex multi-stage amplification, filtering, or modulation / demodulation circuits.

[0055] 5. The control logic is simple, requiring only a single digital signal (MJ_GAIN_SEL) to control a relay, enabling fine-tuning of the gain without complex programming or the use of digital potentiometers. The AD8421 instrumentation amplifier inherently possesses a high common-mode rejection ratio (CMRR), effectively suppressing 50Hz / 60Hz power frequency interference and other common-mode noise carried by the human body. This is crucial for extracting weak bioelectrical signals from the human body surface (whose impedance changes modulate the signal).

[0056] 6. The load effect on the human body being tested is minimal, avoiding the problem of inaccurate impedance measurement caused by factors of the measuring equipment itself. The voltage difference across the skin is extracted by a dedicated differential amplifier (U11), which can effectively suppress common-mode interference (such as environmental electromagnetic noise and electrode contact noise); the AQY221N2S is used, which has low on-resistance and low switching noise compared to traditional mechanical switches or ordinary analog switches, avoiding signal distortion and significantly improving the accuracy of impedance measurement, far exceeding the error level of existing technologies.

[0057] 7. Simultaneously, without altering the core architecture, signal attenuation caused by differences in sensor (electrode) contact with the skin can be compensated by switching the gain. It can automatically switch the amplification factor based on skin impedance, using low gain at low impedance to avoid signal saturation and high gain at high impedance to ensure measurability, thus solving the problem of "either inaccurate measurement or no measurement at all" in existing technologies.

[0058] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. In this invention, it should also be noted that the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, an integrally formed connection, a mechanical connection, or an indirect connection through intermediate connecting parts. The specific meaning of the terms in this utility model can be understood according to the specific circumstances.

[0059] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0060] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A skin impedance detection circuit, applied in a radiofrequency therapy device, characterized in that, include: The detection electrode module is used to form a current detection circuit by contacting human skin. A differential current acquisition circuit, connected in series in the current detection loop, is configured to convert the excitation current flowing through the detection electrode module into a differential voltage signal; A digitally controllable gain amplifier circuit is connected to the output terminal of the differential current acquisition circuit, configured to receive the differential voltage signal and switch the gain level according to the digital control signal, and output the amplified analog signal. as well as The main control module is connected to the digitally controllable gain amplifier circuit and is configured to acquire the amplified analog signal, calculate the skin impedance value by combining the current gain level and known excitation parameters, and generate device control commands based on the skin impedance value.

2. The skin impedance detection circuit according to claim 1, characterized in that, The differential current acquisition circuit includes: A sampling resistor is connected in series in the current detection circuit, and a differential voltage is generated across the sampling resistor when the excitation current flows through it. A filtering unit is connected between the two ends of the sampling resistor and the input terminal of the digitally controllable gain amplifier circuit to filter out high-frequency interference signals.

3. The skin impedance detection circuit according to claim 2, characterized in that, The filtering unit is an RC low-pass filter, which includes resistors connected in series between the two ends of the sampling resistor and the input terminal of the amplifier circuit, and a capacitor connected across the two input terminals of the amplifier circuit.

4. The skin impedance detection circuit according to claim 1, characterized in that, The digitally controllable gain amplifier circuit includes: An instrumentation amplifier has a first input terminal, a second input terminal, an output terminal, a reference voltage terminal, and a gain setting terminal; A variable resistor network, connected to the gain setting terminal, is used to set the amplification factor of the instrumentation amplifier; An electronic switch, controlled by the digital control signal, is configured to be turned on or off to change the equivalent resistance of the variable resistor network; When the electronic switch is in the off state, the variable resistor network exhibits a first resistance value, corresponding to a first gain level; when the electronic switch is in the on state, the variable resistor network exhibits a second resistance value, corresponding to a second gain level; the first resistance value is greater than the second resistance value, making the first gain level less than the second gain level.

5. The skin impedance detection circuit according to claim 4, characterized in that, The variable resistor network includes: A basic resistor branch contains at least one basic resistor; An additional resistor branch, which includes at least one additional resistor; The additional resistor branch and the basic resistor branch are connected in series between the gain setting terminals; The electronic switch is connected in parallel with the additional resistor branch; When the electronic switch is turned off, the additional resistor branch is connected to the circuit, and the equivalent resistance of the variable resistor network is the sum of the resistance values ​​of the basic resistor branch and the additional resistor branch. When the electronic switch is turned on, the additional resistor branch is short-circuited by the electronic switch, and the equivalent resistance of the variable resistor network is the resistance of the basic resistor branch.

6. The skin impedance detection circuit according to claim 5, characterized in that, The electronic switch is an optocoupler, the output terminal of which includes a MOSFET, the drain and source of which are connected in parallel across the two ends of the additional resistor branch, and the input terminal of which receives the digital control signal.

7. The skin impedance detection circuit according to claim 4, characterized in that, The digitally controllable gain amplifier circuit also includes a DC bias unit, which is connected to the reference voltage terminal of the instrumentation amplifier to provide a stable DC reference level so that the output signal is superimposed on a preset DC bias voltage.

8. The skin impedance detection circuit according to claim 1, characterized in that, The main control module is configured to execute the following security control logic: The calculated skin impedance value is compared with a preset safety threshold range; If the skin impedance value exceeds the safety threshold range, a control command is generated to reduce the radio frequency output power or stop the radio frequency output. If the skin impedance value is within the safe threshold range, the current operating state is maintained or power increase is allowed.

9. The skin impedance detection circuit according to claim 1, characterized in that, The excitation current is a radio frequency alternating current, the frequency of which is the same as the operating frequency of the radio frequency therapy device or is a specific detection frequency.

10. A radiofrequency therapy device, characterized in that, Includes a radio frequency energy generation module and a skin impedance detection circuit as described in any one of claims 1 to 9; The radio frequency energy generation module is configured to provide excitation current to the detection electrode module; The device control commands generated by the main control module of the skin impedance detection circuit are connected to the control terminal of the radio frequency energy generation module to adjust the output of radio frequency energy.

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