Radio frequency probe circuit

Abstract

A radio frequency probe circuit comprises an alternating current extraction module, an impedance conversion module, a voltage amplification module and an output module, the alternating current extraction module extracts alternating current components of a preset frequency band in a signal to be detected, so that the frequency of the signal to be detected can be selected; voltage amplitude amplification is carried out on a first alternating current signal in signals to be detected through the voltage amplification module so as to offset signal gain attenuation caused in the coaxial cable signal transmission process, in addition, in order to not affect signal amplification of the voltage amplification module, the output impedance of the voltage amplification module is adjusted to be matched with the voltage amplification module through the impedance conversion module, and the output impedance of the voltage amplification module is adjusted to be matched with the output impedance. The output impedance is adjusted in the output module to be matched with the characteristic impedance of the coaxial cable, so that the characteristic impedance is matched with the input impedance of the radio frequency equipment; therefore, the radio frequency probe circuit provided by the utility model not only can transmit the to-be-detected signal of the predetermined frequency band under the condition that the gain is not changed, but also can perform impedance adjustment.

Description

Technical Field

[0001] This application relates to the technical field of probes, and specifically relates to a radio frequency probe circuit. Background Art

[0002] When radio frequency devices such as spectrum analyzers and network analyzers measure a circuit under test, a coaxial cable is usually used to connect to the circuit under test. However, for some circuits under test of DC power supplies or amplifiers, since the coaxial cable cannot adjust the input impedance and output impedance, a low input impedance will bring a load effect to the circuit under test. After connecting the radio frequency device, it will affect the working state of the circuit under test and accurate measurement results cannot be obtained. In addition, the coaxial cable transmits all-frequency signals to be measured of the circuit under test to the radio frequency device. However, for some circuits under test, only the signals to be measured in a predetermined frequency band need to be input to the radio frequency device. In summary, for some circuits under test such as DC power supplies or amplifiers, a coaxial cable cannot be directly used to connect the circuit under test and the radio frequency device. Utility Model Content

[0003] Considering the above problems, this application provides a radio frequency probe circuit.

[0004] According to one aspect of this application, in one embodiment, a radio frequency probe circuit is provided for connecting a circuit under test and one end of a coaxial cable, and the other end of the coaxial cable is connected to the radio frequency device. The radio frequency probe circuit includes: an AC extraction module, an impedance conversion module, a voltage amplification module, and an output module;

[0005] The AC extraction module is connected to the circuit under test. The AC extraction module is configured to obtain the signal to be measured output by the circuit under test and extract the AC component in the signal to be measured in a predetermined frequency band, and obtain and output a first AC signal;

[0006] The impedance conversion module is connected between the AC extraction module and the voltage amplification module. The impedance conversion module is configured to provide an output impedance matching the voltage amplification module and transmit the first AC signal output by the AC extraction module to the voltage amplification module;

[0007] The voltage amplification module is connected to the output module. The voltage amplification module is configured to amplify the voltage amplitude of the first AC signal by a predetermined amplification factor, and obtain and output a second AC signal;

[0008] The output module is connected to the coaxial cable. The output module is configured to provide an output impedance matching the characteristic impedance of the coaxial cable and output the second AC signal to the coaxial cable, so that the coaxial cable transmits the second AC signal to the radio frequency device.

[0009] In one embodiment, the predetermined frequency band in the signal to be measured is a frequency band greater than the first frequency.

[0010] In one embodiment, the AC extraction module includes a capacitor C1. One end of the capacitor C1 is used to receive the signal to be measured, and the other end of the capacitor C1 is used to output a first AC signal.

[0011] In one embodiment, the impedance conversion module includes: a first RF follower circuit, a first bias current providing circuit, and a first bias voltage providing circuit;

[0012] The first RF follower circuit is used to provide a first output impedance and transmit the first AC signal output by the AC extraction module to the voltage amplification module; wherein, the first output impedance is the input impedance required by the voltage amplification module;

[0013] The first bias current providing circuit is used to provide a first bias current to the first RF follower circuit;

[0014] The first bias voltage providing circuit is used to provide a first bias voltage to the first RF follower circuit.

[0015] In one embodiment, the first RF follower circuit includes: a switching transistor Q2, a resistor R3, and a resistor R4. The control electrode of the switching transistor Q2 receives the first AC signal output by the AC extraction module through the resistor R3. The first electrode of the switching transistor Q2 is connected to the first voltage supply terminal VCC through the resistor R4, and the second electrode of the switching transistor Q2 is used to output the first AC signal;

[0016] And / or, the first bias voltage providing circuit includes: a resistor R1 and a resistor R2. One end of the resistor R1 is connected to the first voltage supply terminal VCC, the other end of the resistor R1 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the second voltage supply terminal VEE; wherein, the connected end of the resistor R1 and the resistor R2 is used to provide the first bias voltage to the first RF follower circuit;

[0017] And / or, the first bias current providing circuit includes: a switching transistor Q3, a resistor R7, a resistor R10, and a resistor R11. The first electrode of the switching transistor Q3 is connected to the output terminal of the first RF follower circuit. The second electrode of the switching transistor Q3 is connected to the second voltage supply terminal VEE through the resistor R7. The control electrode of the switching transistor Q3 is connected to the first voltage supply terminal VCC through the resistor R10, and the control electrode of the switching transistor Q3 is also connected to the second voltage supply terminal VEE through the resistor R11.

[0018] In one embodiment, the voltage amplification module includes: a switching transistor Q1, a resistor R5, and a resistor R6. The second pole of the switching transistor Q1 is connected to one end of the resistor R5, and the other end of the resistor R5 is used to receive the first AC signal output by the impedance conversion module. The first pole of the switching transistor Q1 is connected to one end of the resistor R6, and the other end of the resistor R6 is used to output a second AC signal. The control pole of the switching transistor Q1 is connected to the second voltage supply terminal VEE.

[0019] In one embodiment, the voltage amplification module further includes: a resistor R14, a resistor R15, a resistor R17, a capacitor C4, and a capacitor C5;

[0020] One end of the capacitor C5 is connected to one end of the resistor R5, and the other end of the capacitor C5 is connected to the other end of the resistor R5;

[0021] One end of the resistor R15 is connected to the control pole of the switching transistor Q1, the other end of the resistor R15 is connected to the first voltage supply terminal VCC, one end of the resistor R14 is connected to the control pole of the switching transistor Q1, the other end of the resistor R14 is connected to the second voltage supply terminal VEE, one end of the capacitor C4 is connected to the control pole of the switching transistor Q1, and the other end of the capacitor C4 is connected to the second voltage supply terminal VEE;

[0022] One end of the resistor R17 is connected to the first pole of the switching transistor Q1, and the other end of the resistor R17 is used to receive a predetermined DC voltage.

[0023] In one embodiment, the output module includes: a second RF follower circuit, an output impedance adjustment circuit, and a second bias current supply circuit;

[0024] The second RF follower circuit is used to provide a second output impedance, and at the same time receive the second AC signal output by the voltage amplification module and output the second AC signal to the coaxial cable;

[0025] The output impedance adjustment circuit is used to adjust the second output impedance to a third output impedance, and the third output impedance matches the characteristic impedance of the coaxial cable;

[0026] The second bias current supply circuit is used to provide a second bias current to the second RF follower circuit.

[0027] In one embodiment, the second RF follower circuit includes: a switching transistor Q4, a resistor R6, and a resistor R8. The control pole of the switching transistor Q4 receives the second AC signal output by the voltage amplification module through the resistor R6. The first pole of the switching transistor Q4 is connected to the first voltage supply terminal VCC through the resistor R8, and the second pole of the switching transistor Q4 is used to output the second AC signal;

[0028] And / or, the output impedance adjustment circuit includes a resistor R16, one end of the resistor R16 is connected to the output end of the second radio frequency follower circuit, and the other end of the resistor R16 is used to connect to the coaxial cable;

[0029] And / or, the second bias current providing circuit includes a switching transistor Q5, a resistor R9, a resistor R12, and a resistor R13. The first pole of the switching transistor Q5 is connected to the output end of the second radio frequency follower circuit. The second pole of the switching transistor Q5 is connected to the second voltage supply terminal VEE through the resistor R9. The control pole of the switching transistor Q5 is connected to the first voltage supply terminal VCC through the resistor R12, and the control pole of the switching transistor Q5 is also connected to the second voltage supply terminal VEE through the resistor R13.

[0030] In one embodiment, it further includes:

[0031] A static voltage stabilization module, which is connected to the output module, is used to obtain the second AC signal output by the output module, take the second AC signal as a feedback signal, and adjust the static voltage in the second AC signal output by the voltage amplification module based on the feedback signal, so that the static voltage in the second AC signal output by the output module is a predetermined value;

[0032] And / or, a power supply module, which is used to provide a predetermined voltage for each module of the radio frequency probe circuit.

[0033] According to the radio frequency probe circuit of the above embodiment, including an AC extraction module, an impedance conversion module, a voltage amplification module, and an output module. Since the AC extraction module extracts the AC component in the predetermined frequency band of the signal to be measured, the frequency of the signal to be measured can be selected. And, the voltage amplitude of the first AC signal in the signal to be measured is amplified by the voltage amplification module to offset the signal gain attenuation caused by the coaxial cable during signal transmission. In addition, in order not to affect the signal amplification of the voltage amplification module, the output impedance is adjusted to match the voltage amplification module through the impedance conversion module, and then the output impedance is adjusted in the output module to match the characteristic impedance of the coaxial cable, so as to match the input impedance of the radio frequency device. Thus, the radio frequency probe circuit provided by the present invention can not only transmit the signal to be measured in the predetermined frequency band without change in gain, but also perform impedance adjustment to achieve that the radio frequency probe circuit has a high input impedance and an output impedance matching the radio frequency device. Description of the Drawings

[0034] Figure 1 A schematic diagram of the connection between the circuit under test and the radio frequency device as an example;

[0035] Figure 2 A schematic diagram of the structure of the radio frequency probe circuit in one embodiment;

[0036] Figure 3 Schematic structural diagram of a radio frequency probe circuit according to another embodiment;

[0037] Figure 4 Schematic circuit diagram of a radio frequency probe circuit according to an embodiment;

[0038] Figure 5 Schematic circuit diagram of a power supply module according to an embodiment. Detailed implementation manners

[0039] The present application will be further described in detail below in conjunction with the accompanying drawings through specific implementation manners. Similar elements in different implementation manners adopt related similar element numbers. In the following implementation manners, many detailed descriptions are provided to enable a better understanding of the present application. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification, which is to avoid the core part of the present application being overwhelmed by excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the descriptions in the specification and general technical knowledge in the art.

[0040] In addition, the features, operations, or characteristics described in the specification can be combined in any appropriate manner to form various implementation manners, and the operation steps involved in each embodiment can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the specification and the drawings are only for clearly describing a certain embodiment, and do not mean to be the necessary composition and / or sequence.

[0041] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the described objects and do not have any sequential or technical meaning. And the "connection" and "coupling" mentioned in the present application, unless otherwise specified, both include direct and indirect connection (coupling).

[0042] Please refer to Figure 1 , Figure 1 shows an example of the connection between the circuit under test and the radio frequency device. The circuit under test 10 is connected to the input end of the radio frequency probe circuit 20. The output end of the radio frequency probe circuit 20 is connected to one end of the coaxial cable 30, and the other end of the coaxial cable 30 is connected to the input interface of the radio frequency device 40. In this way, the signal to be measured output by the circuit under test 10 is transmitted to the radio frequency device 40 through the radio frequency probe circuit 20 and the coaxial cable 30 for measurement and analysis. In some embodiments, the circuit under test 10 can be a DC power supply circuit, an amplifier circuit, etc., and the radio frequency device 40 can be a radio frequency analysis instrument such as a spectrum analyzer or a network analyzer.

[0043] In some embodiments, the process of the RF device 40 measuring and analyzing the signal to be measured in the circuit under test 10 is as follows: The RF device 40 outputs a frequency-converted signal to the circuit under test 10. The circuit under test 10 outputs the signal to be measured under the excitation of the frequency-converted signal. The RF device 40 receives the signal to be measured and performs measurement and analysis to obtain the circuit network characteristics of the circuit under test. For example, it can be the trend of the impedance in the circuit under test changing with frequency.

[0044] Based on the above connection example of the circuit under test 10 and the RF device 40, an embodiment of the present application provides an RF probe circuit. Please refer to Figure 2 In some embodiments, the RF probe circuit 20 includes: an AC extraction module 201, an impedance conversion module 202, a voltage amplification module 203, and an output module 204. Among them, the input end of the AC extraction module 201 is connected to the measurement point of the circuit under test 10, the output end of the AC extraction module 201 is connected to the input end of the voltage amplification module 203, the output end of the voltage amplification module 203 is connected to the input end of the output module 204, and the output end of the output module 204 is connected to one end of the coaxial cable 30. The other end of the coaxial cable 30 is connected to the RF device 40.

[0045] The following will separately describe each module in the RF probe circuit 20.

[0046] The AC extraction module 201 is used to obtain the signal to be measured output by the circuit under test 10, extract the AC component in the signal to be measured in a predetermined frequency band, and obtain and output a first AC signal. Since the RF device 40 measures and analyzes the AC component in the signal to be measured, it is necessary to extract the AC component in the signal to be measured in a predetermined frequency band. In one embodiment, the measurement frequency of the RF device 40 is greater than the first frequency, so the predetermined frequency band is the frequency band greater than the first frequency. Usually, the first frequency is a frequency slightly greater than 0. For example, the first frequency can be 5 Hz.

[0047] The impedance conversion module 202 is used to provide an output impedance matching the voltage amplification module 203 and transmit the first AC signal output by the AC extraction module 201 to the voltage amplification module 203.

[0048] Since the voltage amplification module 203 needs to ensure that it has zero input impedance or near-zero input impedance when amplifying the voltage amplitude of a signal, so that it can amplify the voltage amplitude at a predetermined amplification factor. However, the output impedance of the circuit under test 10 is often relatively large, that is, the input impedance of the RF probe circuit 20 is large. Therefore, the impedance conversion module 202 is required to transform the impedance, so that the impedance output by the impedance conversion module 202 to the next-stage circuit (voltage amplification module 203) is close to or equal to 0, thereby ensuring that the voltage amplification module 203 can amplify the voltage amplitude of the signal at a predetermined amplification factor. Thus, in some embodiments, the output impedance provided by the impedance conversion module 202 that matches the voltage amplification module 203 is an output impedance close to or equal to 0.

[0049] In addition, in addition to performing impedance transformation to provide an output impedance that matches the voltage amplification module 203, the impedance conversion module 202 also needs to transmit the input first AC signal to the voltage amplification module 203 while maintaining the characteristics of the first AC signal.

[0050] The voltage amplification module 203 is used to amplify the voltage amplitude of the first AC signal at a predetermined amplification factor to obtain and output a second AC signal. Since the output impedance of the RF probe circuit 20 and the input impedance of the RF device 40 often need to be matched, resulting in some attenuation of the gain of the signal to be measured from the perspective of the circuit under test 10. For example, when the output impedance of the RF probe circuit 20 is the same as the input impedance of the RF device 40, from the perspective of the circuit under test 10, the gain of the signal to be measured will be attenuated by half. Therefore, it is necessary for the voltage amplification module 203 to amplify the voltage amplitude of the first AC signal at a predetermined amplification factor, and the predetermined amplification factor is related to the output impedance of the RF probe circuit 20 and the input impedance of the RF device 40. In one embodiment, the predetermined amplification factor can be 2.

[0051] The output module 204 is used to provide an output impedance that matches the characteristic impedance of the coaxial cable 30 and output the second AC signal to the coaxial cable 30, so that the coaxial cable 30 transmits the second AC signal to the RF device 40. The function of the output module 204 is similar to that of the impedance conversion module 202, both of which are to transform the impedance. In one embodiment, the final output impedance of the output module 204 is the same as the characteristic impedance of the coaxial cable 30. For example, if the characteristic impedance of the coaxial cable 30 is 50Ω, then the output impedance of the output module 204 is also 50Ω. It should be noted that the output impedance of the output module 204 is the output impedance of the RF probe circuit 20.

[0052] In some embodiments, when each module in the RF probe circuit 20 is working, it also needs to provide a stable static operating voltage and a power supply voltage. Please refer to Figure 3, the RF probe circuit of some embodiments further includes: a static voltage stabilization module 205 and a power supply module 206, where:

[0053] The static voltage stabilization module 205 is connected to the output module 204 and the voltage amplification module 203, and is configured to obtain the second AC signal output by the output module 204, use the second AC signal as a feedback signal, and adjust the static voltage in the second AC signal output by the voltage amplification module 203 based on the feedback signal, so that the static voltage in the second AC signal output by the output module 204 is a predetermined value. For example, the predetermined value can be 0 or a value close to 0.

[0054] The power supply module 206 is configured to supply a predetermined voltage to each module of the RF probe circuit 20.

[0055] The above are some descriptions of each module of the RF probe circuit 20.

[0056] In some embodiments, an example of the specific circuit structure of each module in the RF probe circuit 20 is also provided. Please refer to Figure 4 , which will be described in detail below.

[0057] It should be noted that a first voltage supply terminal VCC and a second voltage supply terminal VEE are provided in the RF probe circuit 20, where the first voltage provided by the first voltage supply terminal VCC is greater than the second voltage provided by the second voltage supply terminal VEE.

[0058] The AC extraction module 201 includes a capacitor C1. One end of the capacitor C1 is used to receive the signal to be measured, and the other end of the capacitor C1 is used to output a first AC signal. The first AC signal is a signal in a predetermined frequency band, and the predetermined frequency band is a frequency band greater than the first frequency. The first frequency is determined by the capacitance value of the capacitor C1.

[0059] The impedance conversion module 202 includes: a first RF follower circuit 2021, a first bias current supply circuit 2022, and a first bias voltage supply circuit 2023.

[0060] The first RF follower circuit 2021 is configured to provide a first output impedance and transmit the first AC signal output by the AC extraction module 201 to the voltage amplification module 203; the first output impedance is the input impedance required by the voltage amplification module 203. The first RF follower circuit 2021 has the characteristics of high input impedance and low output impedance, and can keep the original waveform and phase information of the signal unchanged, and then can keep the original characteristics of the signal, so that the first AC signal output by the AC extraction module 201 can be transmitted to the voltage amplification module 203 while keeping the original characteristics. In one embodiment, the first output impedance is 0 or an output impedance close to 0.

[0061] When the first radio frequency follower circuit 2021 operates, it needs to provide a constant bias voltage and bias current. Therefore, in the embodiments of the present application, a first bias current providing circuit 2022 and a first bias voltage providing circuit 2023 are respectively provided to provide a constant bias voltage and bias current to the first radio frequency follower circuit 2021. Among them, the first bias current providing circuit 2022 is used to provide a first bias current to the first radio frequency follower circuit 2021. The first bias voltage providing circuit 2023 is used to provide a first bias voltage to the first radio frequency follower circuit 2021.

[0062] The following is an example of the specific circuit of the impedance conversion module 202:

[0063] The first radio frequency follower circuit 2021 includes: a switching transistor Q2, a resistor R3, and a resistor R4. The control electrode of the switching transistor Q2 receives the first AC signal output by the AC extraction module 201 through the resistor R3. The first electrode of the switching transistor Q2 is connected to the first voltage supply terminal VCC through the resistor R4. The second electrode of the switching transistor Q2 is used to output the first AC signal to the voltage amplification module 203. In one embodiment, the switching transistor Q2 is a junction field effect transistor. The control electrode of the switching transistor Q2 is the gate, the first electrode of the switching transistor Q2 is the drain, and the second electrode of the switching transistor Q2 is the source.

[0064] The first bias voltage providing circuit 2023 includes: a resistor R1 and a resistor R2. One end of the resistor R1 is connected to the first voltage supply terminal VCC. The other end of the resistor R1 is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the second voltage supply terminal VEE. Among them, the connected end of the resistor R1 and the resistor R2 is used to provide a first bias voltage to the first radio frequency follower circuit 2021. Among them, the voltage provided by the first voltage supply terminal VCC is greater than the voltage provided by the second voltage supply terminal VEE. After the resistor R1 and the resistor R2 are voltage-divided according to their respective resistance values, the voltage after voltage division is used as the bias voltage of the first radio frequency follower circuit 2021.

[0065] The first bias current providing circuit 2022 includes: a switching transistor Q3, a resistor R7, a resistor R10, and a resistor R11. The first electrode of the switching transistor Q3 is connected to the output terminal of the first radio frequency follower circuit. The second electrode of the switching transistor Q3 is connected to the second voltage supply terminal VEE through the resistor R7. The control electrode of the switching transistor Q3 is connected to the first voltage supply terminal VCC through the resistor R10. The control electrode of the switching transistor Q3 is also connected to the second voltage supply terminal VEE through the resistor R11. In the embodiments of the present application, the switching transistor Q3, the resistor R7, the resistor R10, and the resistor R11 form a constant current source circuit, which can provide a constant bias current to the first radio frequency follower circuit 2021. Among them, the switching transistor Q3 can be a triode. The control electrode of the switching transistor O3 is the base, the first electrode of the switching transistor O3 is the collector, and the second electrode of the switching transistor O3 is the emitter.

[0066] The voltage amplification module 203 includes: a switching transistor Q1, a resistor R5, and a resistor R6. The second pole of the switching transistor Q1 is connected to one end of the resistor R5, and the other end of the resistor R5 is used to receive the first AC signal output by the impedance conversion module. The first pole of the switching transistor Q1 is connected to one end of the resistor R6, and the other end of the resistor R6 is used to output the second AC signal. The control pole of the switching transistor Q1 is connected to the second voltage supply terminal VEE. Among them, the amplification factor of the signal voltage amplitude of the voltage amplification module 203 is determined by the resistors R5 and R6, and the resistance value ratio of the resistor R6 to the resistor R5 is the predetermined amplification factor of the voltage amplification module 203. For example, if the resistor R6 is 100 Ω and the resistor R5 is 50 ohms, the predetermined amplification factor is 2. In an embodiment, the switching transistor Q1 is a triode, the control pole of the switching transistor Q1 is the base, the first pole of the switching transistor Q1 is the collector, and the second pole of the switching transistor Q2 is the emitter.

[0067] The above circuit of the voltage amplification module 203 also requires a constant bias voltage and bias current, as well as some compensation processing during operation. Therefore, the voltage amplification module 203 further includes: a resistor R14, a resistor R15, a resistor R17, a capacitor C4, and a capacitor C5, where:

[0068] One end of the capacitor C5 is connected to one end of the resistor R5, and the other end of the capacitor C5 is connected to the other end of the resistor R5. The capacitor C5 is used to compensate the high-frequency gain in the first AC signal.

[0069] One end of the resistor R15 is connected to the control pole of the switching transistor Q1, the other end of the resistor R15 is connected to the first voltage supply terminal VCC, one end of the resistor R14 is connected to the control pole of the switching transistor Q1, the other end of the resistor R14 is connected to the second voltage supply terminal VEE, and one end of the capacitor C4 is connected to the control pole of the switching transistor Q1, and the other end of the capacitor C4 is connected to the second voltage supply terminal VEE. Among them, the circuit composed of the resistor R15, the resistor R14, and the capacitor C4 provides a stable bias voltage for the switching transistor Q1.

[0070] One end of the resistor R17 is connected to the first pole of the switching transistor Q1, and the other end of the resistor R17 is used to receive a predetermined DC voltage. The resistor R17 is used to provide a stable bias current for the switching transistor Q1.

[0071] The output module 204 includes: a second radio frequency follower circuit 2041, an output impedance adjustment circuit 2042, and a second bias current supply circuit 2043.

[0072] The second radio frequency follower circuit 2041 is used to provide a second output impedance, receive the second AC signal output by the voltage amplification module 203 at the same time, and output the second AC signal to the coaxial cable 30. Similar to the first radio frequency follower circuit 2021, the second radio frequency follower circuit 2041 has the characteristics of high input impedance and low output impedance, and can keep the original waveform and phase information of the signal unchanged. Subsequently, it can maintain the original characteristics of the signal, so that the second AC signal output by the voltage amplification module 203 can be output to the coaxial cable 30 while maintaining the original characteristics. In one embodiment, the second output impedance is an output impedance of 0 or close to 0.

[0073] The output impedance adjustment circuit 2042 is used to adjust the second output impedance to a third output impedance, and the third output impedance matches the characteristic impedance of the coaxial cable 30. In one embodiment, the characteristic impedance of the coaxial cable 30 is 50Ω. Therefore, the third output impedance is 50Ω.

[0074] The second bias current supply circuit 2043 is used to provide a second bias current to the second radio frequency follower circuit.

[0075] The following is an example of the specific circuit of the output module 204:

[0076] The second radio frequency follower circuit 2041 includes: a switching transistor Q4, a resistor R6, and a resistor R8. The control electrode of the switching transistor Q4 receives the second AC signal output by the voltage amplification module 203 through the resistor R6. The first electrode of the switching transistor Q4 is connected to the first voltage supply terminal VCC through the resistor R8. The second electrode of the switching transistor Q4 is used to output the second AC signal. The switching transistor Q4 is a triode. The control electrode of the switching transistor Q4 is the base. The first electrode of the switching transistor Q4 is the collector. The second electrode of the switching transistor Q4 is the emitter.

[0077] The output impedance adjustment circuit 2042 includes a resistor R16. One end of the resistor R16 is connected to the output terminal of the second radio frequency follower circuit, and the other end of the resistor R16 is used to connect to the coaxial cable 30. The resistor R16 is used to adjust the second output impedance output by the second radio frequency follower circuit 2041 to a third output impedance as the output impedance of the output module 204. Since the second output impedance is an output impedance of 0 or close to 0, the resistance value of the resistor R16 is the resistance value of the third output impedance. For example, when the third output impedance is 50Ω, the resistance value of the resistor R16 is also 50Ω.

[0078] The second bias current supply circuit 2043 includes a switching transistor Q5, a resistor R9, a resistor R12, and a resistor R13. The first pole of the switching transistor Q5 is connected to the output terminal of the second RF follower circuit 2041. The second pole of the switching transistor Q5 is connected to the second voltage supply terminal VEE through the resistor R9. The control pole of the switching transistor Q5 is connected to the first voltage supply terminal VCC through the resistor R12, and the control pole of the switching transistor Q5 is also connected to the second voltage supply terminal VEE through the resistor R13. In this embodiment, the switching transistor Q5, the resistor R9, the resistor R12, and the resistor R13 form a constant current source circuit, which can provide a constant bias current for the second RF follower circuit 2041. Among them, the switching transistor Q5 can be a triode. The control pole of the switching transistor O5 is the base, the first pole of the switching transistor O5 is the collector, and the second pole of the switching transistor O5 is the emitter.

[0079] The static voltage stabilization module 205 includes a resistor R18, an operational amplifier U1, a capacitor C2, and a capacitor C3. Among them, one end of the resistor R18 is connected to the end where the output impedance adjustment circuit 2042 and the output terminal of the second RF follower circuit 2041 are connected. The other end of the resistor R18 is connected to the negative-phase input terminal of the operational amplifier U1. The output terminal of the operational amplifier U1 is connected to the resistor R17 for providing a stable bias current for the switching transistor Q1. The output terminal of the operational amplifier U1 is connected to the ground through the capacitor C3. The positive-phase input terminal of the operational amplifier U1 is connected to the ground. The negative-phase input terminal of the operational amplifier U1 is also connected to its output terminal through the capacitor C2. In addition, the positive power supply terminal of the operational amplifier U1 is connected to the first voltage supply terminal VCC, and the negative power supply terminal of the operational amplifier U1 is connected to the second voltage supply terminal VEE.

[0080] Please refer to Figure 5 , an example of the circuit of the power supply module 206 is: the power supply module 206 includes a first DC power supply V1 and a second DC power supply V2. The negative pole of the first DC power supply V1 is connected to the positive pole of the second DC power supply V2. The negative pole of the first DC power supply V1 and the positive pole of the second DC power supply V2 are also connected to the ground. The positive pole of the first DC power supply V1 is used to connect to the first voltage supply terminal VCC, and the negative pole of the second DC power supply V2 is used to connect to the second voltage supply terminal VEE.

[0081] The above uses specific examples to elaborate on the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For those skilled in the technical field to which the present invention belongs, according to the idea of the present invention, several simple deductions, deformations or substitutions can also be made.

Claims

1. A radio frequency probe circuit, used to connect a circuit under test and one end of a coaxial cable, wherein the other end of the coaxial cable is connected to a radio frequency device, characterized in that: include: AC extraction module, impedance conversion module, voltage amplification module and output module; The AC extraction module is connected to the circuit under test, and is used to obtain the signal under test output by the circuit under test, and extract the AC component of a predetermined frequency band in the signal under test, to obtain and output a first AC signal; The impedance conversion module is connected between the AC extraction module and the voltage amplification module, and is used to provide an output impedance matching the voltage amplification module, and transmit the first AC signal output by the AC extraction module to the voltage amplification module; The voltage amplification module is connected to the output module, and the voltage amplification module is used to amplify the voltage amplitude of the first AC signal according to a predetermined amplification factor to obtain and output a second AC signal; The output module is connected to the coaxial cable, and is used to provide an output impedance matching the characteristic impedance of the coaxial cable, and output the second AC signal to the coaxial cable, so that the coaxial cable transmits the second AC signal to the radio frequency device.

2. The radio frequency probe circuit according to claim 1, characterized in that: The predetermined frequency band in the signal to be tested is a frequency band having a frequency greater than the first frequency.

3. The radio frequency probe circuit according to claim 1 or 2, characterized in that: The AC extraction module includes a capacitor C1 , one end of the capacitor C1 is used to receive the signal to be measured, and the other end of the capacitor C1 is used to output a first AC signal.

4. The radio frequency probe circuit according to claim 1, characterized in that: The impedance conversion module includes: a first radio frequency follower circuit, a first bias current providing circuit and a first bias voltage providing circuit; The first RF follower circuit is used to provide a first output impedance and transmit the first AC signal output by the AC extraction module to the voltage amplification module; wherein the first output impedance is the input impedance required by the voltage amplification module; The first bias current providing circuit is used to provide a first bias current to the first RF follower circuit; The first bias voltage providing circuit is used to provide a first bias voltage to the first RF follower circuit.

5. The radio frequency probe circuit as claimed in claim 4, characterized in that: The first RF follower circuit includes: a switch tube Q2, a resistor R3 and a resistor R4, the control electrode of the switch tube Q2 receives the first AC signal output by the AC extraction module through the resistor R3, the first electrode of the switch tube Q2 is connected to the first voltage supply terminal VCC through the resistor R4, and the second electrode of the switch tube Q2 is used to output the first AC signal; And / or, the first bias voltage providing circuit includes: a resistor R1 and a resistor R2, one end of the resistor R1 is connected to the first voltage providing terminal VCC, the other end of the resistor R1 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the second voltage providing terminal VEE; wherein, the end connected to the resistor R1 and the resistor R2 is used to provide the first bias voltage to the first RF follower circuit; And / or, the first bias current providing circuit includes: a switch tube Q3, a resistor R7, a resistor R10 and a resistor R11, the first electrode of the switch tube Q3 is connected to the output end of the first RF follower circuit, the second electrode of the switch tube Q3 is connected to the second voltage providing end VEE through the resistor R7, the control electrode of the switch tube Q3 is connected to the first voltage providing end VCC through the resistor R10, and the control electrode of the switch tube Q3 is also connected to the second voltage providing end VEE through the resistor R11.

6. The radio frequency probe circuit according to claim 1, characterized in that: The voltage amplification module includes: a switch tube Q1, a resistor R5 and a resistor R6, the second electrode of the switch tube Q1 is connected to one end of the resistor R5, and the other end of the resistor R5 is used to receive the first AC signal output by the impedance conversion module, the first electrode of the switch tube Q1 is connected to one end of the resistor R6, and the other end of the resistor R6 is used to output a second AC signal, and the control electrode of the switch tube Q1 is connected to the second voltage providing end VEE.

7. The radio frequency probe circuit according to claim 6, characterized in that: The voltage amplification module further includes: a resistor R14, a resistor R15, a resistor R17, a capacitor C4 and a capacitor C5; One end of the capacitor C5 is connected to one end of the resistor R5, and the other end of the capacitor C5 is connected to the other end of the resistor R5; One end of the resistor R15 is connected to the control electrode of the switch tube Q1, and the other end of the resistor R15 is connected to the first voltage supply terminal VCC; one end of the resistor R14 is connected to the control electrode of the switch tube Q1, and the other end of the resistor R14 is connected to the second voltage supply terminal VEE; one end of the capacitor C4 is connected to the control electrode of the switch tube Q1, and the other end of the capacitor C4 is connected to the second voltage supply terminal VEE; One end of the resistor R17 is connected to the first electrode of the switch tube Q1 , and the other end of the resistor R17 is used to receive a predetermined DC voltage.

8. The radio frequency probe circuit according to claim 1, characterized in that: The output module includes: a second RF follower circuit, an output impedance adjustment circuit and a second bias current providing circuit; The second RF follower circuit is used to provide a second output impedance, receive a second AC signal output by the voltage amplification module, and output the second AC signal to the coaxial cable; The output impedance adjustment circuit is used to adjust the second output impedance to a third output impedance, and the third output impedance matches the characteristic impedance of the coaxial cable; The second bias current providing circuit is used to provide a second bias current to the second RF follower circuit.

9. The radio frequency probe circuit according to claim 8, characterized in that: The second RF follower circuit includes: a switch tube Q4, a resistor R6 and a resistor R8, the control electrode of the switch tube Q4 receives the second AC signal output by the voltage amplification module through the resistor R6, the first electrode of the switch tube Q4 is connected to the first voltage supply terminal VCC through the resistor R8, and the second electrode of the switch tube Q4 is used to output the second AC signal; And / or, the output impedance adjustment circuit comprises a resistor R16, one end of the resistor R16 is connected to the output end of the second RF follower circuit, and the other end of the resistor R16 is used to connect to the coaxial cable; And / or, the second bias current providing circuit includes a switch tube Q5, a resistor R9, a resistor R12 and a resistor R13, the first electrode of the switch tube Q5 is connected to the output end of the second RF follower circuit, the second electrode of the switch tube Q5 is connected to the second voltage providing end VEE through the resistor R9, the control electrode of the switch tube Q5 is connected to the first voltage providing end VCC through the resistor R12, and the control electrode of the switch tube Q5 is also connected to the second voltage providing end VEE through the resistor R13.

10. The radio frequency probe circuit according to claim 1, characterized in that: Also includes: a static voltage stabilization module, which is connected to the output module and is used to obtain a second AC signal output by the output module, use the second AC signal as a feedback signal, and adjust the static voltage in the second AC signal output by the voltage amplification module based on the feedback signal so that the static voltage in the second AC signal output by the output module is a predetermined value; And / or, a power supply module, used to provide a predetermined voltage to each module of the radio frequency probe circuit.

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