A high common-mode rejection ratio isolated voltage probe for power devices

Abstract

The application discloses a high common-mode rejection ratio isolation voltage probe for a power device, comprising two implementation modes of an analog isolation voltage probe and a digital isolation voltage probe; the analog isolation voltage probe comprises a tip cable, an analog front-end circuit, an analog isolation and signal transmission module; the start and end of the tip cable are connected with a measured device and the analog front-end circuit through radio frequency connectors, and the analog isolation and signal transmission module is connected with the analog front-end circuit and an oscilloscope; the digital isolation voltage probe comprises a tip cable, a signal conditioning circuit, a signal acquisition and transmission module; the start and end of the tip cable are connected with a measured device and the signal conditioning circuit through radio frequency connectors, and the signal acquisition and transmission module is connected with the signal conditioning circuit and a PC end; the tip cable comprises a center conductor layer, a reference conductor layer and a shielding conductor layer, and the layers are electrically isolated through an insulating medium; a ferrite magnetic ring is sleeved outside the shielding conductor layer, and the ferrite magnetic ring is embedded between the reference conductor layer and the shielding conductor layer. The isolation voltage probe has high common-mode rejection ratio and integrability.

Description

Technical Field

[0001] This invention belongs to the field of power device switching voltage measurement technology, specifically a high common-mode rejection ratio isolation voltage probe for power devices. Background Technology

[0002] The switching characteristics of power devices are crucial for the development, optimization, reliable operation, and efficiency improvement of power conversion systems. As a primary parameter for analyzing the switching characteristics of power devices, accurate measurement of switching voltage is key to enabling device condition monitoring, loss calculation, junction temperature extraction, and lifetime prediction. However, with the switching times of wide-bandgap power devices such as SiC and GaN shrinking to the nanosecond level, their switching voltage measurements are affected by strong common-mode disturbances with high transients (hundreds of volts per nanosecond) and high amplitudes (kilovolts). Wideband, highly resistant, highly integrated, and low-intrusion voltage probes are widely used for measuring the switching voltage of power devices. These probes must possess attenuation or even common-mode interference elimination capabilities; otherwise, errors will increase, severely impacting the accuracy of the measurement results.

[0003] Currently, voltage probes are mainly divided into two types: differential voltage probes and optically isolated voltage probes. The common-mode rejection performance of differential voltage probes is highly dependent on the symmetry of the differential structure. Parasitic parameters will cause impedance mismatch in the differential path, thereby reducing the common-mode rejection ratio at high frequencies. Optically isolated voltage probes have excellent common-mode rejection performance, but they suffer from temperature drift and require repeated calibration during use. Their internal electro-optic crystals have defects such as strong aging effects and poor linearity, and they are also extremely expensive. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a high common-mode rejection ratio (CMRR) isolated voltage probe for power devices, specifically designed for measuring voltage signal fluctuations. This isolated voltage probe includes both analog and digital isolation voltage probes. While meeting performance requirements such as bandwidth, withstand voltage, noise immunity, and invasiveness, it offers advantages such as high CMRR, low cost, integrability, and real-time measurement, making it suitable for high-performance testing and applications of voltage signals from wide-bandgap power devices such as SiC MOSFETs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high common-mode rejection ratio isolation voltage probe for power devices is characterized by including two implementation methods: an analog isolation voltage probe and a digital isolation voltage probe.

[0007] The analog isolation voltage probe includes a tip cable, an analog front-end circuit, and an analog isolation and signal transmission module. The beginning and end of the tip cable are connected to the device under test and the analog front-end circuit respectively through radio frequency connectors. The analog isolation and signal transmission module is connected to both the analog front-end circuit and the oscilloscope.

[0008] The analog front-end circuit includes a choke circuit, an attenuation circuit, a buffer circuit, and a filter circuit. The choke circuit includes a first common-mode choke coil, the attenuation circuit includes voltage-dividing resistors R1 and R2 and voltage-dividing capacitors C1 and C2, the buffer circuit includes resistors R3, R4, and R5 and a first operational amplifier, and the filter circuit includes a first filter. The first common-mode choke coil is connected to the end of a pointed cable via an RF connector. One coil of the first common-mode choke coil is connected to the input path of the differential-mode signal, and the other coil is connected to the return path of the differential-mode signal. One end of resistor R1 connected in parallel with voltage divider capacitor C1 is connected to one of the coils of the first common-mode choke and the differential-mode signal input path, and the other end is connected to one end of resistor R3; one end of voltage divider resistor R2 connected in parallel with voltage divider capacitor C2 is grounded, and the other end is connected to one end of resistor R3, and the other end of resistor R3 is connected to the non-inverting input of the first operational amplifier; the two ends of resistor R4 are connected to the inverting input and output of the first operational amplifier, respectively, and the two ends of resistor R5 are connected to the output of the first operational amplifier and the input of the first filter.

[0009] Furthermore, the digital isolation voltage probe includes a tip cable, a signal conditioning circuit, and a signal acquisition and transmission module; the beginning and end of the tip cable are connected to the device under test and the signal conditioning circuit respectively through RF connectors, and the signal acquisition and transmission module is connected to both the signal conditioning circuit and the PC.

[0010] The signal conditioning circuit includes a choke circuit, an attenuation circuit, a buffer circuit, a bias circuit, a gain circuit, a filter circuit, and an analog-to-digital conversion circuit. The choke circuit includes a second common-mode choke coil; the attenuation circuit includes voltage-dividing resistors R6 and R7 and voltage-dividing capacitors C3 and C4; the buffer circuit includes resistors R8 and R9 and a second operational amplifier; and the bias circuit includes an input resistor R... i Reference resistor R ref and grounding resistance R g The gain circuit includes resistor R 10 R 11 The circuit includes a third operational amplifier, a second filter, and an analog-to-digital converter circuit including an analog-to-digital converter and an isolation power supply circuit.

[0011] The second common-mode choke is connected to the end of the tip cable via an RF connector. One coil of the second common-mode choke is connected to the input path of the differential-mode signal, and the other coil is connected to the return path of the differential-mode signal. One end of the parallel connection of voltage divider resistor R6 and voltage divider capacitor C3 is connected to one coil of the second common-mode choke and the input path of the differential-mode signal, and the other end is connected to one end of resistor R8. One end of the parallel connection of voltage divider resistor R7 and voltage divider capacitor C4 is grounded, and the other end is connected to one end of resistor R8. The other end of resistor R8 is connected to the non-inverting input of the second operational amplifier. The two ends of resistor R9 are connected to the inverting input and output of the second operational amplifier, respectively. The input resistor R... i One end is connected to the output of the second operational amplifier, and the other end is connected to the non-inverting input of the third operational amplifier; reference resistor R ref One end is connected to the reference voltage, and the other end is connected to the non-inverting input of the third operational amplifier; grounding resistor R g One end is grounded, and the other end is connected to the non-inverting input of the third operational amplifier; resistor R 10 One end of the resistor is grounded, and the other end is connected to the inverting input of the third operational amplifier; resistor R 11 The two ends of the first filter are connected to the inverting input and output of the third operational amplifier; one end of the second filter is connected to the output of the third operational amplifier, and the other end is connected to the input of the analog-to-digital converter; the upper limit port and lower limit port of the analog-to-digital converter are connected to the isolation power supply circuit.

[0012] Furthermore, the tip cable includes a center conductor layer, a reference conductor layer, and a shielding conductor layer, with each layer electrically isolated from the others by an insulating medium; a ferrite magnetic ring is sleeved on the outside of the shielding conductor layer, and a ferrite magnetic ring is embedded between the reference conductor layer and the shielding conductor layer.

[0013] Furthermore, the first filter and the second filter are one of a low-pass filter, a Bessel filter, and a Butterworth filter.

[0014] Furthermore, the signal acquisition and transmission module includes a digital isolator, an FPGA, a gigabit Ethernet network, and a host computer; the FPGA is connected to the digital isolator and also connected to the host computer via gigabit Ethernet.

[0015] Furthermore, the analog isolation and signal transmission module includes an analog isolator and a lossless transmission line; the analog isolator is connected to a filter and is also connected to the analog input port of an oscilloscope via the lossless transmission line.

[0016] Compared with existing technologies, the advantages of this invention are:

[0017] 1. Based on the isolation method of breaking the grounding loop, the analog isolation voltage probe uses an analog isolator, and the digital isolation voltage probe uses a digital isolator. This eliminates the direct electrical connection between the measurement signal input and output, achieving current isolation between the front and rear stages, and eliminating the impedance path through which common-mode current is directly coupled to ground. Compared to differential voltage probes based on balanced circuits, the isolation voltage probe of this invention has certain advantages in common-mode rejection performance. Ferrite rings are inserted outside the shielding conductor layer of the tip cable and between the reference conductor layer and the shielding conductor layer, thereby introducing common-mode impedance to attenuate and filter out common-mode signals. Simultaneously, common-mode signals are further suppressed through choke circuits and more compact analog front-end circuits, thereby improving the common-mode rejection ratio of the isolation voltage probe.

[0018] 2. The isolation voltage probe of this invention employs an isolation method based on the principle of magnetic coupling using an RF balun coupler or a digital isolator. Compared to the optical isolation voltage probe, which is based on the principle of single-stage electro-optic modulation, this invention offers significant cost advantages and temperature stability. It avoids the temperature drift and aging problems associated with optical isolation voltage probes during use, making it suitable for large-scale applications. The isolation voltage probe of this invention uses a PCB printed circuit board as its primary carrier, and since the circuitry containing power devices typically also requires a PCB, this invention exhibits high integrability.

[0019] 3. The digital isolation voltage probe of this invention can visualize measurement results without relying on an oscilloscope. The digital isolation voltage probe achieves the conversion of the measured signal from the analog domain to the digital domain through a signal conditioning circuit, and realizes the acquisition and transmission of digital signals through a field-programmable gate array (FPGA) and Gigabit Ethernet, and visualizes the measurement results on a host PC. Existing differential voltage probes and optically isolated voltage probes transmit the measured voltage signal in the analog domain. Due to the influence of parasitic factors in the signal transmission line, the length of the signal transmission line connecting to the oscilloscope is significantly limited. However, the measured voltage signal of the digital isolation voltage probe is transmitted in the digital domain, and the length of the Gigabit Ethernet cable can be adjusted according to the usage requirements of different application scenarios. Attached Figure Description

[0020] Figure 1 Schematic diagram for simulating an isolation voltage probe;

[0021] Figure 2 This is a schematic diagram of a digital isolation voltage probe.

[0022] Figure 3 This is a structural diagram of a tip cable;

[0023] Figure 4 The topology diagram of the analog front-end circuit for simulating an isolation voltage probe;

[0024] Figure 5 The topology diagram of the signal conditioning circuit for a digital isolation voltage probe;

[0025] Figure 6 This is a structural diagram of the signal acquisition and transmission module for a digital isolation voltage probe. Detailed Implementation

[0026] Specific embodiments will be given below with reference to the accompanying drawings. These specific embodiments are only used to illustrate the technical solution of the present invention in detail, but are not intended to limit the scope of protection of this application.

[0027] This invention proposes a high common-mode rejection ratio isolation voltage probe for power devices (hereinafter referred to as isolation voltage probe, see [link]). Figures 1-6 It includes two implementation methods: analog isolated voltage probe and digital isolated voltage probe. While meeting the performance requirements of wide bandwidth, strong anti-interference, low interference and high withstand voltage, it has the advantages of high common mode rejection ratio, low cost, integrability and real-time measurement, and is suitable for voltage measurement of power devices such as SiC MOSFET.

[0028] like Figure 1 As shown, the analog isolation voltage probe comprises three parts: a tip cable, an analog front-end circuit, and an analog isolation and signal transmission module. The tip cable is connected to the device under test (DUT) and the analog front-end circuit via RF connectors. The analog isolation and signal transmission module is connected to both the analog front-end circuit and the oscilloscope. The voltage signal from the DUT is transmitted to the tip cable via the RF connector. The tip cable attenuates and filters the common-mode signal in the DUT signal. The analog front-end circuit further processes the DUT signal. The analog isolation and signal transmission module performs analog isolation on the DUT signal after it has been processed by the analog front-end circuit, and simultaneously transmits the processed DUT signal to the oscilloscope to visualize the DUT signal.

[0029] like Figure 3As shown, the tip cable includes a center conductor layer, a reference conductor layer, and a shielding conductor layer, each made of metal, and electrically isolated from each other using an insulating medium. At the beginning and end of the tip cable, the reference conductor layer and the shielding conductor layer are connected to the ground terminals of the corresponding RF connectors. A ferrite core is sleeved over the shielding conductor layer to insert common-mode impedance, and multiple single-turn ferrite cores are connected in series to avoid magnetic saturation of the ferrite cores. The sleeve length is four-fifths of the tip cable length, ensuring that the isolation voltage probe can be bent during use while minimizing common-mode current. A ferrite core is embedded between the reference conductor layer and the shielding conductor layer to increase the common-mode impedance of the reference conductor layer relative to the shielding conductor layer, further decoupling common-mode and differential-mode signals. The tip cable structure includes, but is not limited to, the optimized tri-coaxial tip cable structure of this invention. It aims to achieve a flow path where the central conductor layer serves as the outflow path for differential-mode signals, the reference conductor layer as the return path for differential-mode signals, and the shielding conductor layer as the flow path for common-mode signals. This minimizes the common-mode current introduced by the device under test while establishing shunt paths for both common-mode and differential-mode currents, allowing the common-mode current to be attenuated and filtered out as it passes through the tip cable. Theoretically, the common-mode signal will be attenuated by A when passing through a single-turn ferrite core. f times (0 < A) f <1), corresponding to the common-mode attenuation factor A of the measurement system. CM It will be reduced to A f A CM Attenuation coefficient A f Depending on the permeability of the ferrite core, its core shape parameters, and the signal frequency, using the tip cable of this invention, the common-mode rejection ratio (CMRR) of the measurement system will theoretically be improved by -20 nlgA. f dB, where n represents the number of turns of the ferrite magnetic ring.

[0030] like Figure 4 As shown, the analog front-end circuit uses a PCB printed circuit board as a carrier and includes four parts: a choke circuit, an attenuation circuit, a buffer circuit, and a filter circuit. The choke circuit includes a first common-mode choke CMC1, the attenuation circuit includes voltage divider resistors R1 and R2 and voltage divider capacitors C1 and C2, the buffer circuit includes resistors R3, R4, and R5 and a first operational amplifier OPA1, and the filter circuit includes a first filter.

[0031] The first common-mode choke CMC1 is connected to the end of the tip cable via an RF connector. One coil of CMC1 is connected to the input path of the differential-mode signal, and the other coil is connected to the return path of the differential-mode signal, filtering out residual common-mode signals flowing from the tip cable to the analog front-end circuit. One end of the parallel connection of voltage divider resistor R1 and voltage divider capacitor C1 is connected to one coil of the first common-mode choke CMC1 connected to the input path of the differential-mode signal, and the other end is connected to one end of resistor R3. One end of the parallel connection of voltage divider resistor R2 and voltage divider capacitor C2 is grounded, and the other end is connected to one end of resistor R3. The voltage division ratio of the probe is R1 / R2 or C1 / C2. The non-inverting input of the first operational amplifier OPA1 is connected to the other end of resistor R3. Resistor R3 is used to eliminate noise signals generated by the first operational amplifier OPA1. Resistor R4 is a feedback resistor, with its two ends connected to the inverting input and output of the first operational amplifier OPA1, respectively, to reduce the impact of subsequent circuitry on signal attenuation. Resistor R5 is a damping resistor, connected at both ends to the output of the first operational amplifier OPA1 and the input of the first filter. It dampens the resonance between the probe's grounding capacitance and the parasitic inductance of the transmission line in the probe at high frequencies, thus smoothing the probe's amplitude-frequency response curve. The first filter can be one of a low-pass filter, Bessel filter, or Butterworth filter, used to filter out high-frequency signals. It is worth noting that parasitic capacitance still exists between the analog front-end circuitry of this isolated voltage probe and ground, providing a coupling path for common-mode interference. Therefore, the PCB layout must maintain the compactness of the analog front-end circuitry.

[0032] like Figure 4 As shown, the analog isolation and signal transmission module includes an analog isolator and a lossless transmission line. The analog isolator is connected to a filter and also to the analog input port of the oscilloscope via the lossless transmission line. The analog isolator provides analog isolation for the measured voltage signal processed by the analog front-end circuit, and the lossless transmission line transmits the measured voltage signal processed by the analog isolator to the oscilloscope. The analog isolator includes, but is not limited to, an RF balun coupler, whose structure can be equivalent to an ideal transformer with a 1:1 turns ratio. The primary side (PRI) of the RF balun coupler is connected to the filter, and the secondary side (SEC) is connected to the oscilloscope via the lossless transmission line. The RF balun coupler achieves matching, conversion, and isolation of unbalanced signals to balanced signals, and physically isolates the common-mode current loop caused by common ground. The lossless transmission line uses an SMA to BNC RF signal line to transmit the measured voltage signal processed by the analog isolator to the oscilloscope, realizing the visualization of the voltage signal. The measured voltage signal is always transmitted in the probe in the form of an analog signal.

[0033] like Figure 2As shown, the digital isolated voltage probe comprises three parts: a tip cable, a signal conditioning circuit, and a signal acquisition and transmission module. The beginning and end of the tip cable are connected to the device under test (DUT) and the signal conditioning circuit, respectively, via RF connectors. The signal acquisition and transmission module is connected to both the signal conditioning circuit and the PC. The voltage signal of the DUT is transmitted to the tip cable via the RF connector. The tip cable attenuates and filters the common-mode signal in the DUT signal. The signal conditioning circuit converts the DUT signal from an analog signal to a digital signal. The signal acquisition and transmission module transmits the DUT signal processed by the signal conditioning circuit to the PC, thus realizing the visualization of the DUT signal.

[0034] The difference between digital and analog isolated voltage probes lies in the conversion of the measured voltage signal into the digital domain. Digital isolation is achieved through wireless transmission, digital isolators, or digital fiber optics. The advantages of digital isolated voltage probes are that they avoid distortion caused by parasitic parameters in long-distance analog transmission and allow visualization of measurement results without the need for an oscilloscope. However, prior to digital isolation, the measured voltage signal in a digital isolated voltage probe requires signal conditioning circuitry to adjust and convert the analog signal to a digital signal.

[0035] like Figure 5 As shown, the signal conditioning circuit uses a PCB printed circuit board as its carrier and includes a choke circuit, an attenuation circuit, a buffer circuit, a bias circuit, a gain circuit, a filter circuit, and an analog-to-digital converter circuit. The choke circuit includes a second common-mode choke CMC2, the attenuation circuit includes voltage divider resistors R6 and R7 and voltage divider capacitors C3 and C4, the buffer circuit includes resistors R8 and R9 and a second operational amplifier OPA2, and the bias circuit includes an input resistor R... i Reference resistor R ref and grounding resistance R g The gain circuit is used to adjust the magnitude of the voltage signal to suit the voltage input range of the analog-to-digital converter (ADC), and includes resistor R. 10 R 11 And the third operational amplifier OPA3; the filtering circuit includes a second filter, the analog-to-digital conversion circuit includes an analog-to-digital converter ADC and an isolation power supply circuit;

[0036] The second common-mode choke CMC2 is connected to the end of the tip cable via an RF connector. One coil of CMC2 is connected to the input path of the differential-mode signal, and the other coil is connected to the return path of the differential-mode signal to filter out residual common-mode signals in the measured voltage signal. One end of the parallel connection of voltage divider resistor R6 and voltage divider capacitor C3 is connected to one coil of the second common-mode choke CMC2 connected to the input path of the differential-mode signal, and the other end is connected to one end of resistor R8. One end of the parallel connection of voltage divider resistor R7 and voltage divider capacitor C4 is grounded, and the other end is connected to one end of resistor R8. The voltage division ratio of the probe is R6 / R7 or C3 / C4. The non-inverting input of the second operational amplifier OPA2 is connected to the other end of resistor R8. Resistor R8 is used to eliminate noise signals generated by the second operational amplifier OPA2. Resistor R9 is a feedback resistor, with its two ends connected to the inverting input and output of the second operational amplifier OPA2, respectively, to reduce the impact of subsequent circuitry on signal attenuation. Input resistor R... i One end is connected to the output of the second operational amplifier OPA2, and the other end is connected to the non-inverting input of the third operational amplifier OPA3. The input resistor R i It acts as a damping resistor to prevent resonance between the probe's grounding capacitance and the transmission line's parasitic inductance at high frequencies; the reference resistor R ref One end is connected to the reference voltage V ref Reference voltage V ref Powered by a regulated power supply module with its own independent power supply, the other end of which is connected to the non-inverting input of the third operational amplifier OPA3; grounding resistor R g One end is grounded, and the other end is connected to the non-inverting input of the third operational amplifier, OPA3. Resistor R 10 One end of the resistor is grounded, and the other end is connected to the inverting input of the third operational amplifier OPA3; resistor R 11 One end is connected to the inverting input of the third operational amplifier OPA3, and the other end is connected to the output of the third operational amplifier OPA3. The second filter uses one of the following: a low-pass filter, a Bessel filter, or a Butterworth filter. One end is connected to the output of the third operational amplifier OPA3, and the other end is connected to the input of the analog-to-digital converter (ADC) to filter out high-frequency signals. The upper limit reference voltage port V of the ADC... RB and the lower limit port of the reference voltage V RT Each is connected to an isolation power supply circuit, which provides a stable reference voltage for the analog-to-digital converter (ADC).

[0037] The signal conditioning circuit obtains the measured voltage V in The analog voltage V input to the analog-to-digital converter (ADC) ADC The transitive relationship is as follows:

[0038]

[0039] In the formula, G i G ref G g The input resistances R are respectively i Reference resistor R ref and grounding resistance R g The electrical conductivity;

[0040] The analog-to-digital converter (ADC) will convert the analog voltage V ADC When converted to a digital signal, the conversion relationship is as follows:

[0041]

[0042] In the formula, V out denoted as , where is the output voltage of the analog-to-digital converter (ADC), and n is the number of bits in the ADC.

[0043] Because converting the measured voltage into an analog signal easily causes signal distortion, digital isolated voltage probes adopt a design approach that integrates digital signal acquisition, transmission, and display. For example... Figure 6 As shown, the signal acquisition and transmission module includes a digital isolator, a field-programmable gate array (FPGA), a gigabit Ethernet (GbE) port, and a host computer (PC). The multiple isolation channels of the digital isolator are connected one by one to the binary output ports D0-D7 of the analog-to-digital converter (ADC) (taking an 8-bit ADC as an example). The FPGA is connected to the digital isolator and also to the host computer (PC) via gigabit Ethernet (GbE). High-speed data acquisition is performed through the FPGA, and high-speed digital signal real-time transmission is achieved with the help of gigabit Ethernet (GbE), which is then displayed in real time on the host computer (PC).

[0044] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A high common mode rejection ratio isolated voltage probe for power devices, characterized by, The analog isolated voltage probe and the digital isolated voltage probe are two implementation manners; The analog isolated voltage probe comprises a tip cable, an analog front-end circuit, and an analog isolation and signal transmission module; the start and end of the tip cable are connected with a measured device and the analog front-end circuit through radio frequency connectors, and the analog isolation and signal transmission module is connected with the analog front-end circuit and an oscilloscope; The analog front-end circuit comprises a choke circuit, an attenuation circuit, a buffer circuit and a filter circuit; the choke circuit comprises a first common-mode choke coil, the attenuation circuit comprises voltage dividing resistors R 1、 R 2 and voltage dividing capacitors C 1、 C 2, the buffer circuit comprises resistors R 3、 R 4 、R 5 and a first operational amplifier, and the filter circuit comprises a first filter; wherein the first common-mode choke coil is connected to the end of the tip cable through a radio frequency connector, one coil of the first common-mode choke coil is connected to the input path of the differential mode signal, and the other coil is connected to the return path of the differential mode signal; one end of the voltage dividing resistors R 1 and the voltage dividing capacitors C 1 in parallel is connected to the coil of the first common-mode choke coil and the input path of the differential mode signal, and the other end is connected to one end of the resistors R 3; one end of the voltage dividing resistors R 2 and the voltage dividing capacitors C 2 in parallel is grounded, and the other end is connected to one end of the resistors R 3, and the other end of the resistors R 3 is connected to the non-inverting input terminal of the first operational amplifier; the two ends of the resistors R 4 are respectively connected to the inverting input terminal and the output terminal of the first operational amplifier, and the two ends of the resistors R 5 are connected to the output terminal of the first operational amplifier and the input terminal of the first filter. The digital isolated voltage probe comprises a tip cable, a signal conditioning circuit, and a signal acquisition and transmission module; the start and end of the tip cable are connected with a measured device and the signal conditioning circuit through radio frequency connectors, and the signal acquisition and transmission module is connected with the signal conditioning circuit and a PC end; The signal conditioning circuit comprises a choke circuit, an attenuation circuit, a buffer circuit, a bias circuit, a gain circuit, a filter circuit and an analog-digital conversion circuit; the choke circuit comprises a second common-mode choke coil, the attenuation circuit comprises a voltage dividing resistor R 6、 R 7 and a voltage dividing capacitor C 3、 C 4, the buffer circuit comprises a resistor R 8、 R 9 and a second operational amplifier, the bias circuit comprises an input resistor R i , a reference resistor R ref and a ground resistor R g , the gain circuit comprises a resistor R 10 、 R 11 and a third operational amplifier, the filter circuit comprises a second filter, and the analog-digital conversion circuit comprises an analog-digital converter and an isolated power supply circuit; The second common mode choke is connected with the end of the tip cable through the radio frequency connector, one coil of the second common mode choke is connected with the input path of the differential mode signal, and the other coil is connected with the return path of the differential mode signal; the voltage dividing resistor R 6 is connected with the voltage dividing capacitor C 3 in parallel, one end of the parallel connection is connected with the coil of the second common mode choke connected with the input path of the differential mode signal, and the other end is connected with one end of the resistor R 8; the voltage dividing resistor R 7 is connected with the voltage dividing capacitor C 4 in parallel, one end of the parallel connection is grounded, and the other end is connected with one end of the resistor R 8, and the other end of the resistor R 8 is connected with the non-inverting input terminal of the second operational amplifier; the two ends of the resistor R 9 are respectively connected with the inverting input terminal and the output terminal of the second operational amplifier, and the input resistor R i is connected with the output terminal of the second operational amplifier at one end and with the non-inverting input terminal of the third operational amplifier at the other end; the reference resistor R ref is connected with the reference voltage ， at one end and with the non-inverting input terminal of the third operational amplifier at the other end; the grounding resistor R g is connected with the non-inverting input terminal of the third operational amplifier at one end and with the inverting input terminal of the third operational amplifier at the other end; the resistor R 10 is grounded at one end and connected with the inverting input terminal of the third operational amplifier at the other end; the resistor R 11 is connected with the inverting input terminal and the output terminal of the third operational amplifier at the two ends; one end of the second filter is connected with the output terminal of the third operational amplifier, and the other end is connected with the input terminal of the analog-to-digital converter; the reference voltage upper limit port and the reference voltage lower limit port of the analog-to-digital converter are connected with the isolation power supply circuit.

2. The high common-mode rejection ratio isolated voltage probe for power devices of claim 1, wherein, The tip cable comprises a center conductor layer, a reference conductor layer, and a shielding conductor layer, and the layers are electrically isolated through an insulating medium; an iron oxide magnetic ring is sleeved outside the shielding conductor layer, and an iron oxide magnetic ring is embedded between the reference conductor layer and the shielding conductor layer.

3. The high common-mode rejection ratio isolated voltage probe for power devices of claim 1, wherein, The first filter and the second filter are one of a low-pass filter, a Bessel filter, and a Butterworth filter.

4. The high common-mode rejection ratio isolated voltage probe for power devices of claim 1, wherein, The signal acquisition and transmission module comprises a digital isolator, an FPGA, a gigabit Ethernet, and a host computer; the FPGA is connected with the digital isolator and is connected with the host computer through the gigabit Ethernet.

5. The high common-mode rejection ratio isolated voltage probe for power devices of claim 1, wherein, The analog isolation and signal transmission module comprises an analog isolator and a lossless transmission line; the analog isolator is connected with the filter and is connected with an analog input port of the oscilloscope through the lossless transmission line.

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