Directional coupler circuits, circuit boards and RF measurement equipment

Abstract

This application provides a directional coupler circuit, circuit board, and radio frequency measurement device, relating to the field of electronic circuit technology. It solves the problem that radio frequency measurement devices in related technologies are difficult to adapt to low-frequency and high-frequency signals. The directional coupler circuit of this application can expand its operating frequency range by using DC, low-frequency, and high-frequency signals. It adopts a high-low frequency separation method, amplifies the high and low frequencies separately, and merges them at the third port. Moreover, each port is a port to ground, which helps to extract signals and enables the directional coupler circuit to have better passband flatness and high-frequency characteristics.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a directional coupler circuit, circuit board, and radio frequency measurement device. Background Technology

[0002] Radio frequency (RF) measurement equipment in the field of RF measurement, such as network analyzers and signal source analyzers, all have a core functional unit: the directional coupler. The function of the directional coupler is to couple only the reverse wave signal while isolating the forward wave signal, thereby measuring the energy of the reflected wave.

[0003] Two commonly used directional coupler structures in related technologies are transmission line couplers and bridge couplers. Transmission line couplers utilize the signal wave transmission characteristics, so their signal bandwidth is related to the length L of the coupling line. However, their effective bandwidth is ineffective near DC or near twice the center frequency. Bridge couplers can transmit DC, but because one of their ports is not grounded, the signal cannot be directly extracted and must be converted using a differential amplifier or a balun (a type of transformer). However, differential amplifiers generally have bandwidths below 10 GHz and significant noise, while baluns typically operate at frequencies above 50 MHz and cannot simultaneously measure high and low frequencies. Therefore, RF measurement equipment in related technologies has significant limitations and is difficult to adapt to both low and high frequency signals. Summary of the Invention

[0004] This application provides a directional coupler circuit, circuit board, and radio frequency measurement device, which solves the problem that radio frequency measurement devices in related technologies are difficult to adapt to low-frequency and high-frequency signals. The directional coupler circuit of this solution has an operating frequency range from DC to high frequency, and has better passband flatness and high-frequency characteristics.

[0005] In a first aspect, this application provides a directional coupler circuit, which has a grounded first port, a second port and a third port. The directional coupler circuit includes a signal input module, an RF amplification module, a low-frequency amplification module and a signal output module.

[0006] The first access terminal of the signal access module is connected to the first port through the first resistor, and the first access terminal of the signal access module is also connected to the second port. The second access terminal of the signal access module is connected to the first port through the second resistor, and the second access terminal of the signal access module is also grounded through the third resistor. The signal access module is used to provide input impedance and to separate DC and low-frequency signals and high-frequency signals in the input signal to be measured.

[0007] The input terminal of the RF amplifier module is connected to the high-frequency output terminal of the signal input module. The RF amplifier module is used to amplify high-frequency signals.

[0008] The first input terminal of the low-frequency amplifier module is connected to the second input terminal of the signal access module, and the second input terminal of the low-frequency amplifier module is connected to the impedance output terminal of the signal access module. The low-frequency amplifier module is used to amplify DC and low-frequency signals, and the amplification factor of the low-frequency amplifier module is matched with the amplification factor of the radio frequency amplifier module.

[0009] The first input terminal of the signal output module is connected to the output terminal of the low-frequency amplifier module, the second input terminal of the signal output module is connected to the output terminal of the radio frequency amplifier module, and the output terminal of the signal output module is connected to the third port.

[0010] Secondly, this application also provides a circuit board that includes the directional coupler circuit described in the first aspect.

[0011] Thirdly, this application also provides a radio frequency measurement device, which includes the circuit board as described in the second aspect.

[0012] The directional coupler circuit of this application can accept DC, low-frequency and high-frequency signals, thus expanding its operating frequency range. It adopts a high-low frequency separation method, amplifies the high and low frequencies separately and merges them at the third port. Moreover, each port is a ground port, which helps to extract signals and enables the directional coupler circuit to have better passband flatness and high-frequency characteristics. Attached Figure Description

[0013] Figure 1 A schematic diagram of a transmission line coupler provided for related technologies;

[0014] Figure 2 A schematic diagram of a bridge coupler provided for related technologies;

[0015] Figure 3 A schematic block diagram of a directional coupler circuit provided in an embodiment of this application;

[0016] Figure 4 An equivalent circuit diagram of a signal access module provided in an embodiment of this application;

[0017] Figure 5 This is a schematic diagram of the circuit structure of a directional coupler circuit provided in an embodiment of this application. Detailed Implementation

[0018] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the embodiments of this application and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, the accompanying drawings only show the parts related to the embodiments of this application, not all structures. Those skilled in the art, after reading this specification, should be able to conceive that any combination of technical features can constitute an optional implementation method, provided that the technical features do not contradict each other.

[0019] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects, not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship. In the description of this application, "multiple" means two or more, and "several" means one or more.

[0020] As a core functional unit of RF measurement equipment in the field of RF measurement, such as network analyzers and signal source analyzers, the directional coupler's function is to couple only the reverse wave signal while isolating the forward wave signal, thereby measuring the energy of the reflected wave.

[0021] In related technologies, transmission line couplers or bridge couplers are typically used as directional couplers, see reference. Figure 1 and Figure 2 ,in, Figure 1 A schematic diagram of a transmission line coupler provided for related technologies. Figure 2 This is a schematic diagram of a bridge coupler provided for related technologies. It is understandable that transmission line couplers are designed using the wave characteristics of radio frequency signals. Due to the wave characteristics on a transmission line, a signal can only be received at the near signal source end and not at the far signal source end. Therefore, port P3 is isolated from port P1 and can only couple to the signal transmitted from port P2. The bridge coupler uses the bridge balance principle. When resistors R1', R2', R3', and R4' are all equal to the target characteristic impedance, the voltage across resistor R3', which is the voltage Vr3 at port P3, is only related to the signal transmitted from port P2 and has no relation to the signal transmitted from port P1.

[0022] Therefore, transmission line couplers utilize the signal wave transmission characteristics, so their signal bandwidth is related to the length L of the coupled line. For example, if the propagation delay of the signal on this length is t, then its effective bandwidth is within the frequency range of one end where the center frequency is 1 / (4t). It is ineffective near DC or near twice the center frequency. While bridge couplers can transmit DC, because its port P3 is not a ground port, the signal cannot be directly extracted and must be converted using a differential amplifier or balun. However, differential amplifiers generally have bandwidths below 10GHz and significant noise. Baluns typically have low frequencies above 50MHz and cannot simultaneously measure high and low frequencies.

[0023] In response, this application provides a directional coupler circuit that is applicable to DC signals, thereby enabling its operating frequency range to extend from DC to high frequencies. Figure 3 A schematic block diagram of a directional coupler circuit provided in one embodiment of this application is shown below. Figure 3 As shown, the directional coupler circuit is provided with a grounded first port, a second port and a third port. The directional coupler circuit includes a signal input module 101, an RF amplification module 102, a low-frequency amplification module 103 and a signal output module 104.

[0024] The first port, the second port, and the third port are all grounded. The first access terminal of the signal access module 101 is connected to the first port through the first resistor R1, and the first access terminal of the signal access module 101 is also connected to the second port. The second access terminal of the signal access module 101 is connected to the first port through the second resistor R2, and the second access terminal of the signal access module 101 is also grounded through the third resistor R3.

[0025] The input terminal of the RF amplifier module 102 is connected to the high-frequency output terminal of the signal access module 101. The first input terminal of the low-frequency amplifier module 103 is connected to the second input terminal of the signal access module 101, and the second input terminal of the low-frequency amplifier module 103 is connected to the impedance output terminal of the signal access module 101.

[0026] The first input terminal of the signal output module 104 is connected to the output terminal of the low-frequency amplifier module 103, the second input terminal of the signal output module 104 is connected to the output terminal of the radio frequency amplifier module 102, and the output terminal of the signal output module 104 is connected to the third port.

[0027] Understandably, the signal input module 101 provides input impedance and separates the DC, low-frequency, and high-frequency signals in the input measured signal. The high-frequency signal then enters the radio frequency (RF) amplification module 102, which amplifies it; while the DC and low-frequency signals enter the low-frequency amplification module 103, which amplifies them. It is noteworthy that the amplification factor of the low-frequency amplification module 103 matches that of the RF amplification module 102, meaning their amplification factors are equal, thus amplifying the DC, low-frequency, and high-frequency signals by the same factor.

[0028] Therefore, the directional coupler circuit of this application can expand its operating frequency range by using DC, low-frequency and high-frequency signals. It adopts a high-low frequency separation method, amplifies the high and low frequencies separately and merges them at the third port. Moreover, each port is a port to ground, which helps to extract signals and enables the directional coupler circuit to have better passband flatness and high-frequency characteristics.

[0029] In one embodiment, the signal access module includes a first capacitor, a fourth resistor, and a first transformer. Specifically, the first terminal of the first capacitor is connected to the second and third resistors, and the second terminal of the first capacitor is connected to the first input terminal of the first transformer. The first terminal of the fourth resistor is connected to the first terminal of the first capacitor, and the second terminal of the fourth resistor is connected to the second terminal of the first capacitor, meaning the fourth resistor is connected in parallel with the first capacitor. Furthermore, the first terminal of the fourth resistor serves as the second input terminal of the signal access module, and the second terminal of the fourth resistor serves as the impedance output terminal of the signal access module. The resistance value of the fourth resistor is matched to the equivalent input resistance of the RF amplification module, ensuring impedance matching of the directional coupler circuit.

[0030] In addition, the second input terminal of the first transformer is connected to the first resistor, the first output terminal of the first transformer is grounded, the second input terminal of the first transformer serves as the first input terminal of the signal access module, the second output terminal of the first transformer serves as the signal output terminal of the signal access module, and the equivalent inductance of the first transformer is equal to the product of the capacitance of the first capacitor and the square of the resistance of the fourth resistor, so that the signal access module can be further equivalent to a resistor with a fixed resistance value (i.e., the fourth resistor).

[0031] It is understandable that, after performing an equivalent transformation on the first transformer, the following can be obtained: Figure 4 The equivalent circuit diagram shown is as follows. Figure 4This is an equivalent circuit diagram of a signal access module provided in one embodiment of this application. Resistor R10 is the equivalent input resistance of the RF amplification module to ground, which is equivalent to a resistor connected in parallel with the parasitic inductance of the first transformer. In the diagram, the parasitic inductance L2 is connected in series with the first capacitor C1, the fourth resistor R4 is connected in parallel with the first capacitor C1, and resistor R10 is connected in parallel with the parasitic inductance L2. Furthermore, the resistance values ​​of the fourth resistor R4 and the resistor R10 are equal, thus making the input impedance of the circuit equivalent to the resistance value of the fourth resistor R4. This also makes the signal access module equivalent to a resistor with a fixed resistance value relative to the signal to be measured, thereby better matching the system and facilitating more accurate signal measurement.

[0032] Therefore, after the signal to be measured enters the signal access module, under the action of the first capacitor C1, high-frequency signals will pass through the first capacitor C1, while DC and low-frequency signals will enter the low-frequency amplification module through the fourth resistor R4. Additionally, under the action of the parasitic inductance L2, DC and low-frequency signals will pass through the parasitic inductance L2, while high-frequency signals will enter the RF amplification module through resistor R10. When the fourth resistor R4 and the tenth resistor R10 are equal, and the equivalent inductance of the first transformer is equal to the product of the capacitance of the first capacitor and the square of the resistance of the fourth resistor, the signal to be measured entering the signal access module is equivalent to being connected to a resistor of a fixed value. The resistance values ​​of the fourth resistor R4 and the tenth resistor R10 can be matched to the required equivalent resistance; for example, if the required equivalent resistance is 50Ω, then the resistance values ​​of both the fourth resistor R4 and the tenth resistor R10 are 50Ω. Therefore, the signal access module can use the first capacitor and the first transformer to isolate high-frequency signals from the low-frequency amplification module and DC and low-frequency signals from the radio frequency amplification module, thereby enabling the measurement of DC and low-frequency signals and high-frequency signals, which helps to expand the operating frequency range of the circuit.

[0033] It should be noted that, in one embodiment, the ratio of the input impedance to the output impedance of the first transformer is 1:1. For example, a 1:1 balun is used as the transformer in the signal access module to transmit high-frequency signals to the radio frequency amplification module.

[0034] In one embodiment, the low-frequency amplification module includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, and an operational amplifier. Specifically, the first terminal of the fifth resistor is connected to the second input terminal of the signal access module, the second terminal of the fifth resistor is connected to the first terminal of the sixth resistor, the second terminal of the fifth resistor is connected to the non-inverting input terminal of the operational amplifier, and the second terminal of the sixth resistor is grounded. The first terminal of the seventh resistor is connected to the impedance output terminal of the signal access module, the second terminal of the seventh resistor is connected to the inverting input terminal of the operational amplifier, the first terminal of the eighth resistor is connected to the second terminal of the seventh resistor, the second terminal of the eighth resistor is connected to the output terminal of the operational amplifier, and the first terminal of the ninth resistor is connected to the output terminal of the operational amplifier.

[0035] Among them, the first end of the fifth resistor serves as the first input terminal of the low-frequency amplifier module, the first end of the seventh resistor serves as the second input terminal of the low-frequency amplifier module, the second end of the ninth resistor serves as the output terminal of the low-frequency amplifier module, and the resistance value of the ninth resistor is matched with the equivalent output resistance of the radio frequency amplifier module.

[0036] It should be noted that, in one embodiment, the input impedance provided by the signal access module includes a fourth resistor. Correspondingly, the fifth and seventh resistors in the low-frequency amplification module are much larger than the fourth resistor. For example, the ratio of the resistance of the fifth resistor to the resistance of the fourth resistor and the ratio of the resistance of the seventh resistor to the resistance of the fourth resistor are both greater than or equal to 100, that is, the resistance of the fifth resistor and the resistance of the seventh resistor are both 100 times or more of the resistance of the fourth resistor.

[0037] In one embodiment, the signal output module includes a first inductor and a second capacitor. Specifically, the first end of the first inductor is connected to the output terminal of the low-frequency amplification module, the first end of the second capacitor is connected to the output terminal of the radio frequency amplification module, and the second end of the first inductor is connected to the second end of the second capacitor. The first inductor is used to conduct the amplified DC and low-frequency signals, the second capacitor is used to conduct the amplified high-frequency signals, and the reactance ratio of the first inductor and the second capacitor matches the reactance ratio of the signal input module.

[0038] Understandably, by utilizing the characteristics of the second capacitor and the first inductor, the signal output module can further separate the input signal. The signal passing through the first inductor retains the DC and low-frequency signals, while the signal passing through the second capacitor retains the high-frequency signals. Therefore, the first inductor is connected to the output of the low-frequency amplification module, and the second capacitor is connected to the output of the RF amplification module, thus enabling the input and output of the amplified signal. Therefore, through the signal output module, the front-end amplification circuit can receive amplified DC, low-frequency, and high-frequency signals, thereby providing the amplified measurement signal to the subsequent circuits, achieving a better signal-to-noise ratio and voltage standing wave ratio.

[0039] Figure 5 The figure shows a schematic diagram of the circuit structure of a directional coupler circuit provided in an embodiment of this application. In one embodiment, ports P1, P2 and P3 in the directional coupler circuit are respectively used as the first port, the second port and the third port, and are all grounded.

[0040] Port P1 is connected to port P2 via a first resistor R1, and port P1 is connected to a grounded third resistor R3 via a second resistor R2. The signal input module in the directional coupler circuit includes a first capacitor C1, a fourth resistor R4, and a first transformer B1. Specifically, the first terminal of the first capacitor C1 is connected to the second resistor R2 and the third resistor R3, and the second terminal of the first capacitor C1 is connected to the first input terminal of the first transformer B1. The first terminal of the fourth resistor R4 is connected to the first terminal of the first capacitor C1, and the second terminal of the fourth resistor R4 is connected to the second terminal of the first capacitor C1; that is, the fourth resistor R4 is connected in parallel with the first capacitor C1.

[0041] Furthermore, the first terminal of the fourth resistor R4 serves as the second input terminal of the signal input module, and the second terminal of the fourth resistor R4 serves as the impedance output terminal of the signal input module. The resistance value of the fourth resistor R4 is matched to the equivalent input resistance of the RF amplifier module, ensuring impedance matching of the directional coupler circuit.

[0042] In addition, the second input terminal of the first transformer B1 is connected to the first resistor R1, the first output terminal of the first transformer B1 is grounded, the second input terminal of the first transformer B1 serves as the first input terminal of the signal access module, and the second output terminal of the first transformer B1 serves as the signal output terminal of the signal access module.

[0043] The low-frequency amplification module includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, and an operational amplifier U1. Specifically, the first terminal of the fifth resistor R5 is connected to the first terminal of the fourth resistor R4, the second terminal of the fifth resistor R5 is connected to the first terminal of the sixth resistor R6, the second terminal of the fifth resistor R5 is connected to the non-inverting input terminal of the operational amplifier U1, and the second terminal of the sixth resistor R6 is grounded.

[0044] The first end of the seventh resistor R7 is connected to the second end of the fourth resistor R4. The second end of the seventh resistor R7 is connected to the inverting input of the operational amplifier U1. The first end of the eighth resistor R8 is connected to the second end of the seventh resistor R7. The second end of the eighth resistor R8 is connected to the output of the operational amplifier U1. The first end of the ninth resistor R9 is connected to the output of the operational amplifier U1.

[0045] Additionally, the RF amplifier module is marked with a dashed box in the figure. This part represents the equivalent input resistance (i.e., resistance R10) and equivalent output resistance (i.e., resistance R11) of the RF amplifier module.

[0046] The signal output module includes a first inductor L1 and a second capacitor C2. Specifically, the first end of the first inductor L1 is connected to the second end of R9, the first end of the second capacitor C2 is connected to the resistor R11, and the second end of the first inductor L1 is connected to the second end of the second capacitor C2.

[0047] Among them, the fifth resistor R5 and the seventh resistor R7 are both much larger than the fourth resistor R4, that is, the resistance values ​​of the fifth resistor R5 and the seventh resistor R7 are 100 times or more than the resistance value of the fourth resistor R4. The fourth resistor R4 is matched with resistor R10, and the ninth resistor R9 is matched with resistor R11. The equivalent inductance value of the first transformer is equal to the product of the capacitance value of the first capacitor and the square of the resistance value of the fourth resistor. The reactance ratio corresponding to the first inductor L1 and the second capacitor C2 is the first reactance ratio value, which is the product of the ninth resistor R9 and the equivalent output resistance of the RF amplifier module (i.e., resistor R11). Moreover, the equivalent reactance ratio corresponding to the first transformer and the first capacitor is the second reactance ratio value, which is equal to the first reactance ratio value.

[0048] Understandably, under the influence of the first capacitor C1, high-frequency signals pass through it, while DC and low-frequency signals enter the low-frequency amplification module through the fourth resistor R4. Additionally, under the influence of the parasitic inductance of the first transformer B1, DC and low-frequency signals pass through it, while high-frequency signals enter the radio frequency (RF) amplification module through resistor R10. The operational amplifier U1 and the differential amplifier circuit formed by the corresponding resistors further amplify the DC and low-frequency signals before they pass through the RF amplification module. Similarly, based on the characteristics of the first inductor L1 and the second capacitor C2, the first inductor L1 is connected to the output terminal of the low-frequency amplification module (i.e., the second end of the ninth resistor R9), and the second capacitor C2 is connected to the output terminal of the RF amplification module (one end of resistor R11 in the figure), thereby realizing the input and output of the amplified signals.

[0049] Therefore, the directional coupler circuit of this application can replace the resistor located between ports P2 and P3 in the bridge coupler with a first transformer, a first capacitor, and a fourth resistor, thereby converting the third port from a differential port to a single-ended port to ground. This makes each port a ground port, which helps in signal extraction. The directional coupler circuit thus exhibits better passband flatness and high-frequency characteristics. Furthermore, this circuit employs a high-low frequency separation method, amplifying high and low frequencies separately and converging them at the third port. This prevents DC signals from entering the RF amplifier module and affecting its operation, allowing DC and low-frequency signals to enter the low-frequency amplifier module. Consequently, the operating frequency range of the circuit is expanded, enabling it to operate from DC to high frequencies.

[0050] It should be noted that in some embodiments, the RF amplification module can use an RF amplification circuit, such as an operational amplifier in-phase RF amplification circuit or a low-noise amplification circuit, to amplify high-frequency signals; in addition, the RF amplification module can also use an RF amplifier to amplify high-frequency signals.

[0051] This application embodiment also provides a circuit board including the directional coupler circuit provided in the above embodiment. The circuit board can separate and amplify DC, low-frequency and high-frequency signals, and ground each port, which helps to extract signals. The signals are then combined at the third port, thereby expanding the operating frequency range of the circuit and enabling it to operate from DC to high frequency.

[0052] This application also provides an RF measurement device, which includes the circuit board provided in the above embodiments. This RF measurement device is capable of measuring DC, low-frequency, and high-frequency signals, and also has better passband flatness and high-frequency characteristics. Furthermore, the operating frequency range of this RF measurement device is expanded, enabling it to operate from DC to high frequencies.

[0053] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0054] Note that the above are merely preferred embodiments and the technical principles employed in this application. Those skilled in the art will understand that this application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of this application, the scope of which is determined by the scope of the appended claims.

Claims

1. A directional coupler circuit, characterized in that, The directional coupler circuit is provided with a grounded first port, a second port, and a third port, and the directional coupler circuit includes: A signal access module, wherein the first access terminal of the signal access module is connected to the first port through a first resistor, and the first access terminal of the signal access module is also connected to the second port; the second access terminal of the signal access module is connected to the first port through a second resistor, and the second access terminal of the signal access module is also grounded through a third resistor; the signal access module is used to provide input impedance and to separate DC and low-frequency signals and high-frequency signals in the input signal to be measured. An RF amplifier module, wherein the input terminal of the RF amplifier module is connected to the high-frequency output terminal of the signal access module, and the RF amplifier module is used to amplify the high-frequency signal; A low-frequency amplification module, wherein the first input terminal of the low-frequency amplification module is connected to the second input terminal of the signal access module, and the second input terminal of the low-frequency amplification module is connected to the impedance output terminal of the signal access module; the low-frequency amplification module is used to amplify the DC and low-frequency signals, and the amplification factor of the low-frequency amplification module is matched with the amplification factor of the radio frequency amplification module. A signal output module, wherein the first input terminal of the signal output module is connected to the output terminal of the low-frequency amplification module, the second input terminal of the signal output module is connected to the output terminal of the radio frequency amplification module, and the output terminal of the signal output module is connected to the third port; The signal output module includes a first inductor and a second capacitor. The first end of the first inductor is connected to the output end of the low-frequency amplification module, the first end of the second capacitor is connected to the output end of the radio frequency amplification module, and the second end of the first inductor is connected to the second end of the second capacitor. The first inductor is used to conduct amplified DC and low-frequency signals, and the second capacitor is used to conduct amplified high-frequency signals. The reactance ratio of the first inductor and the second capacitor is matched with the reactance ratio of the signal input module. Wherein, when the output resistance of the low-frequency amplification module is the ninth resistance, the reactance ratio corresponding to the first inductor and the second capacitor is the first reactance ratio value, and the value of the first reactance ratio value is the product of the resistance of the ninth resistance and the equivalent output resistance of the radio frequency amplification module. Furthermore, when the signal access module includes a first transformer and a first capacitor connected in series, the equivalent reactance ratio corresponding to the first transformer and the first capacitor is a second reactance ratio value, and the second reactance ratio value is equal to the first reactance ratio value.

2. The directional coupler circuit according to claim 1, characterized in that, The signal access module includes a first capacitor, a fourth resistor, and a first transformer; The first terminal of the first capacitor is connected to the second resistor and the third resistor. The second terminal of the first capacitor is connected to the first input terminal of the first transformer. The first terminal of the fourth resistor is connected to the first terminal of the first capacitor. The second terminal of the fourth resistor is connected to the second terminal of the first capacitor. The first terminal of the fourth resistor serves as the second input terminal of the signal access module. The second terminal of the fourth resistor serves as the impedance output terminal of the signal access module. The resistance value of the fourth resistor is matched with the equivalent input resistance of the RF amplifier module. The second input terminal of the first transformer is connected to the first resistor, the first output terminal of the first transformer is grounded, the second input terminal of the first transformer serves as the first input terminal of the signal access module, the second output terminal of the first transformer serves as the signal output terminal of the signal access module, and the equivalent inductance of the first transformer is equal to the product of the capacitance of the first capacitor and the square of the resistance of the fourth resistor.

3. The directional coupler circuit according to claim 2, characterized in that, The ratio of the input impedance to the output impedance of the first transformer is 1:

1.

4. The directional coupler circuit according to claim 1, characterized in that, The low-frequency amplification module includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, and an operational amplifier; The first end of the fifth resistor is connected to the second input terminal of the signal access module, the second end of the fifth resistor is connected to the first end of the sixth resistor, the second end of the fifth resistor is connected to the non-inverting input terminal of the operational amplifier, and the second end of the sixth resistor is grounded. The first end of the seventh resistor is connected to the impedance output terminal of the signal access module, the second end of the seventh resistor is connected to the inverting input terminal of the operational amplifier, the first end of the eighth resistor is connected to the second end of the seventh resistor, the second end of the eighth resistor is connected to the output terminal of the operational amplifier, and the first end of the ninth resistor is connected to the output terminal of the operational amplifier. Wherein, the first end of the fifth resistor serves as the first input terminal of the low-frequency amplification module, the first end of the seventh resistor serves as the second input terminal of the low-frequency amplification module, the second end of the ninth resistor serves as the output terminal of the low-frequency amplification module, and the resistance value of the ninth resistor is matched with the equivalent output resistance of the radio frequency amplification module.

5. The directional coupler circuit according to claim 4, characterized in that, When the input impedance provided by the signal access module includes a fourth resistor, the ratio of the resistance of the fifth resistor to the resistance of the fourth resistor and the ratio of the resistance of the seventh resistor to the resistance of the fourth resistor are both greater than or equal to 100.

6. A circuit board, characterized in that, The circuit board is a directional coupler circuit as described in any one of claims 1-5.

7. A radio frequency measurement device, characterized in that, The radio frequency measurement device includes the circuit board as described in claim 6.

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