A high-speed differential signal impedance matching circuit and its impedance matching method

Abstract

The present application belongs to the field of high-speed signal transmission technology, and specifically discloses a high-speed differential signal impedance matching circuit and an impedance matching method thereof. The circuit includes: a main resistance calibration module, a calibration signal circuit and a calibration circuit; the calibration signal circuit includes a secondary resistance calibration module; the first output end of the calibration circuit is respectively connected to the main resistance calibration module and the secondary resistance calibration module; the calibration signal circuit is connected to the calibration circuit; the calibration signal circuit is used to input a reference voltage and an adjustment voltage to the calibration circuit; the calibration circuit is used to adjust the first equivalent resistance value based on the reference voltage and the adjustment voltage until the target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistance, and the second equivalent resistance value of the main resistance calibration module matches the characteristic impedance of the differential signal transmission circuit. Through the present application, the effect of automatic calibration of impedance matching can be achieved, the efficiency of impedance matching can be improved, and the impedance calibration accuracy is high.

Description

Technical Field

[0001] The present application belongs to the technical field of high-speed signal transmission, and more specifically, relates to a high-speed differential signal impedance matching circuit and an impedance matching method thereof. Background Art

[0002] In high-speed differential signal transmission systems, such as High Definition Multimedia Interface (HDMI) systems and DisplayPort (DP) systems, high-speed signals will encounter transmission line reflection problems during transmission, resulting in signal integrity being compromised. Therefore, in order to achieve reflection-free transmission and maximum power transmission in the transmission system, it is necessary to add an impedance matching circuit to the system circuit to ensure that the signal avoids transmission line reflection during transmission and optimizes system performance.

[0003] In the prior art, when the integration of the signal transmission system is not high, technicians can match the impedance by manual adjustment. However, with the rapid development of high-speed signal transmission technology, the integration of the system is getting higher and higher, and the complexity of the circuit is getting higher and higher. The manual adjustment method becomes complicated and inefficient, and the impedance calibration accuracy that can be achieved is also low, which affects the transmission performance of the high-speed differential signal transmission system.

[0004] Therefore, how to better achieve impedance matching in high-speed differential signal transmission systems has become a technical problem that needs to be urgently solved in the industry. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present application is to better achieve impedance matching in a high-speed differential signal transmission system.

[0006] To achieve the above objectives, in a first aspect, the present application provides a high-speed differential signal impedance matching circuit, which is applied to a differential signal transmission circuit, comprising:

[0007] A main resistance calibration module, a calibration signal circuit and a calibration circuit; the calibration signal circuit includes a secondary resistance calibration module; the first output end of the calibration circuit is connected to the main resistance calibration module and the secondary resistance calibration module respectively; the calibration signal circuit is connected to the calibration circuit;

[0008] The calibration signal circuit is used to input a reference voltage and an adjustment voltage to the calibration circuit; the adjustment voltage is determined based on the first equivalent resistance value of the secondary resistor calibration module;

[0009] The calibration circuit is used to adjust the first equivalent resistance value based on the reference voltage and the adjustment voltage until a target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistance, and the second equivalent resistance value of the main resistance calibration module matches the characteristic impedance of the differential signal transmission circuit; the first equivalent resistance value is equal to the target multiple of the second equivalent resistance value.

[0010] Optionally, the calibration signal circuit further includes a mirror current source, a reference resistor and a first switch tube;

[0011] One end of the reference resistor and one end of the auxiliary resistor calibration module are both connected to a power supply, and the other end of the reference resistor, the source of the first switch tube and the first input end of the calibration circuit are connected in common, so that the first branch where the reference resistor is located inputs the reference voltage to the calibration circuit;

[0012] The drain of the first switch tube is connected to the first output end of the mirror current source, and the gate of the first switch tube is connected to the second output end of the calibration circuit;

[0013] The other end of the secondary resistor calibration module, the second input end of the calibration circuit and the second output end of the mirror current source are connected in common, so that the second branch where the secondary resistor calibration module is located inputs the adjustment voltage to the calibration circuit.

[0014] Optionally, the calibration circuit includes a comparator, an operational amplifier and a digital calibration module;

[0015] The positive input terminal of the comparator serves as the first input terminal of the calibration circuit, and the negative input terminal of the comparator serves as the second input terminal of the calibration circuit; the output terminal of the digital calibration module serves as the first output terminal of the calibration circuit, and the output terminal of the operational amplifier serves as the second output terminal of the calibration circuit;

[0016] The positive input terminal of the comparator is connected to the negative input terminal of the operational amplifier; the output terminal of the comparator is connected to the input terminal of the digital calibration module; the positive input terminal of the operational amplifier is used to input a reference voltage.

[0017] Optionally, the mirror current source is used to provide two identical currents, wherein one current flows through the first branch and the other current flows through the second branch;

[0018] The operational amplifier is used to provide the reference voltage and clamp the voltage on the first branch to the reference voltage;

[0019] The comparator is used to compare the reference voltage with the adjustment voltage;

[0020] The digital calibration module is used to output a calibration control signal to the auxiliary resistance calibration module according to a comparison result output by the comparator, so as to adjust the first equivalent resistance value.

[0021] Optionally, the reference voltage is provided by a bandgap reference circuit.

[0022] Optionally, the main resistance calibration module and the auxiliary resistance calibration module both include multi-way switch branches connected in parallel, and each of the switch branches includes a second switch tube and a resistor connected in sequence;

[0023] Among them, in the arrangement order of the switch branches, except the first switch branch, the other switch branches are switch control branches, and the resistance of each switch control branch is twice the resistance of the previous switch branch.

[0024] Optionally, each of the switch control branches includes an inverter, an output end of the inverter is connected to the gate of the second switch tube, and an input end of the inverter is used to input a calibration control signal output by the calibration circuit.

[0025] Optionally, the calibration circuit is specifically used for:

[0026] When the adjustment voltage is not greater than the reference voltage, the secondary resistor calibration module is controlled to be incorporated into the next switch control branch that is most recently incorporated into the switch control branch to adjust the first equivalent resistance value and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistor.

[0027] Optionally, the calibration circuit is further used for:

[0028] When the adjustment voltage is greater than the reference voltage, the secondary resistor calibration module is controlled to cancel the incorporation of the most recently incorporated switch control branch, and to incorporate the next switch control branch of the most recently incorporated switch control branch to adjust the first equivalent resistance value, and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistance.

[0029] In a second aspect, the present application provides an impedance matching method applied to any of the above-mentioned high-speed differential signal impedance matching circuits, comprising:

[0030] inputting a reference voltage and an adjustment voltage into the calibration circuit using the calibration signal circuit;

[0031] The calibration circuit is used to compare the reference voltage and the adjustment voltage, and the first equivalent resistance value of the secondary resistor calibration module is continuously adjusted according to the comparison result until a target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistor, and the second equivalent resistance value of the main resistor calibration module matches the characteristic impedance of the differential signal transmission circuit.

[0032] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art:

[0033] The present application provides a high-speed differential signal impedance matching circuit and an impedance matching method thereof. The circuit includes a main resistance calibration module, a calibration signal circuit and a calibration circuit. The calibration signal circuit includes a secondary resistance calibration module. By considering the characteristic that the characteristic impedance to be matched in the differential signal transmission circuit is relatively small, a calibration mechanism is designed to calibrate a large resistor to proportionally calibrate a small resistor. By comparing the reference voltage output by the calibration signal circuit and the adjustment voltage based on the output of the secondary resistance calibration module, the calibration circuit is triggered to continuously adjust the equivalent resistance value of the secondary resistance calibration module until a target calibration control signal is output so that the equivalent resistance value of the secondary resistance calibration module reaches the resistance value of the reference resistor. At this time, under the action of the target calibration control signal, the equivalent resistance value of the main resistance calibration module can be matched with the characteristic impedance of the differential signal transmission circuit, thereby achieving the effect of automatic calibration of impedance matching and improving the efficiency of impedance matching. The impedance calibration has high accuracy and effectively improves the transmission performance of the high-speed signal transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is one of the structural schematic diagrams of the high-speed differential signal impedance matching circuit provided in the embodiment of the present application;

[0035] Figure 2 It is a structural schematic diagram of a high-speed differential signal transmission system provided in an embodiment of the present application;

[0036] Figure 3 This is the second structural schematic diagram of the high-speed differential signal impedance matching circuit provided in the embodiment of the present application;

[0037] Figure 4 It is one of the circuit structure diagrams of the resistance calibration module provided in the embodiment of the present application;

[0038] Figure 5 This is the second circuit structure diagram of the resistance calibration module provided in the embodiment of the present application;

[0039] Figure 6 It is a flow chart of a method for calibrating a primary and secondary resistor calibration module by a calibration circuit provided in an embodiment of the present application;

[0040] Figure 7 It is a flow chart of the impedance matching method provided in the embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] The terms "first" and "second" in the specification and claims herein are used to distinguish different objects rather than to describe a specific order of objects. For example, the first equivalent resistance value and the second equivalent resistance value are used to distinguish the equivalent resistance values ​​of the main and auxiliary resistance calibration modules rather than to describe a specific order of equivalent resistance values; the first switch tube and the second switch tube are used to distinguish different switch tubes rather than to describe a specific order of switch tubes, etc.

[0043] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0044] In the description of the embodiments of the present application, unless otherwise specified, "multi-way" means two or more ways. For example, a multi-way switch branch refers to two or more switch branches.

[0045] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0046] Figure 1 This is one of the structural schematic diagrams of a high-speed differential signal impedance matching circuit provided in an embodiment of the present application. The circuit can be applied to a differential signal transmission circuit. The circuit includes:

[0047] A main resistance calibration module 1, a calibration signal circuit 2 and a calibration circuit 3; the calibration signal circuit 2 includes a secondary resistance calibration module 21; the first output end of the calibration circuit 3 is respectively connected to the main resistance calibration module 1 and the secondary resistance calibration module 21; the calibration signal circuit 2 is connected to the calibration circuit 3;

[0048] The calibration signal circuit 2 is used to input a reference voltage and an adjustment voltage to the calibration circuit 3; the adjustment voltage is determined based on the first equivalent resistance value of the secondary resistor calibration module 21;

[0049] The calibration circuit 3 is used to adjust the first equivalent resistance value based on the reference voltage and the adjustment voltage until a target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistance, and the second equivalent resistance value of the main resistance calibration module 1 matches the characteristic impedance of the differential signal transmission circuit; the first equivalent resistance value is equal to the second equivalent resistance value of the target multiple.

[0050] Specifically, the main resistance calibration module described in the embodiment of the present application refers to a module used to calibrate the resistance value of the matching resistor on the positive and negative differential signal transmission lines in the differential signal transmission circuit, so that the resistance value of the matching resistor is equal to the characteristic impedance Z0 on the transmission line, thereby achieving impedance matching.

[0051] Figure 2 is a schematic diagram of the structure of a high-speed differential signal transmission system provided in an embodiment of the present application, such as Figure 2 As shown, the high-speed differential signal transmission system includes a characteristic impedance Z0 on the differential signal transmission line, and selects the power supply VDD as the common mode level connected to the matching resistor R 主 To improve the driving capability of the circuit, a transient voltage suppressor diode (TVS) is selected and connected in parallel on the transmission line to enhance the electrostatic discharge (ESD) performance and ensure the signal integrity of high-speed signals. The characteristic impedance Z0 of the positive and auxiliary lines of the transmitting end is respectively matched with the matching resistor R 主 The resistance values ​​need to be as equal as possible to achieve impedance matching and suppress reflections at the load end.

[0052] It can be understood that the matching resistor R 主 The resistance value is the equivalent resistance value of the main resistance calibration module.

[0053] The secondary resistance calibration module described in the embodiment of the present application refers to a module used to assist in calibrating the equivalent resistance value of the main resistance calibration module.

[0054] In an embodiment of the present application, the main and auxiliary resistance calibration modules can adopt a parallel multi-channel resistance branch structure, and by selecting an external calibration control signal, resistors of different numbers of branches are incorporated to achieve adjustment of the equivalent resistance values ​​of the main and auxiliary resistance calibration modules.

[0055] The first equivalent resistance value described in the embodiment of the present application refers to the resistance value of the equivalent resistance of the secondary resistance calibration module.

[0056] The second equivalent resistance value described in the embodiment of the present application refers to the resistance value of the equivalent resistance of the main resistance calibration module.

[0057] It should be noted that impedance matching means that during the signal transmission process, all high-frequency signals can be transmitted to the load point, and there will be no signal reflection back to the source point, thereby improving the signal output efficiency of the transmission system.

[0058] In the embodiments of the present application, considering the small characteristic impedance Z0 that needs to be matched in the differential signal transmission circuit, the characteristic impedance Z0 is usually around tens of ohms. For example, the characteristic impedance on the transmission line in the HDMI system is generally 50Ω. The resulting resistance value has a small calibration range, and direct calibration will make it impossible to guarantee the calibration accuracy.

[0059] Therefore, in order to improve the calibration accuracy of impedance matching, the present application designs a calibration mechanism for calibrating a large resistor to calibrate a small resistor in proportion, using a secondary resistor calibration module with a larger equivalent resistance value and a secondary resistor calibration module with a smaller equivalent resistance value, and the equivalent resistance value of the secondary resistor calibration module is in a target multiple relationship with the equivalent resistance value of the main resistor calibration module. Among them, the target multiple can be set according to actual needs, for example, the value range that can be set is 100 to 1000 times.

[0060] Among them, the calibration signal circuit used to calibrate the equivalent resistance value of the auxiliary resistor calibration module can adopt a dual-branch circuit structure, one branch is a reference branch, and the other branch is a calibration branch connected in series with the auxiliary resistor calibration module.

[0061] The regulated voltage described in the embodiment of the present application refers to the voltage information on the branch where the secondary resistor calibration module is located, and its magnitude can be determined based on the equivalent resistance value of the secondary resistor calibration module.

[0062] The reference voltage described in the embodiment of the present application refers to a preset reference voltage information on a reference branch, which is used to calibrate the equivalent resistance value of the secondary resistor calibration module.

[0063] In the embodiment of the present application, the calibration signal circuit 2 is connected to the calibration circuit 3, and the calibration signal circuit 2 can adopt a dual-branch circuit structure, wherein a reference resistor is provided on the reference branch to generate a reference voltage, and the reference voltage is input to the calibration circuit 3; the calibration branch outputs a regulation voltage by voltage division through the auxiliary resistor calibration module 21. It can be understood that the magnitude of the regulation voltage changes with the change of the first equivalent resistance value of the auxiliary resistor calibration module 21.

[0064] In the embodiment of the present application, the first output end of the calibration circuit 3 is respectively connected to the main resistance calibration module 1 and the auxiliary resistance calibration module 21. After the calibration circuit 3 receives the reference voltage and the adjustment voltage signal transmitted by the calibration signal circuit 2, it can judge whether the equivalent resistance value of the auxiliary resistance calibration module 21 reaches the resistance value of the reference resistance based on the comparison between the reference voltage and the adjustment voltage, and then adjust the equivalent resistance value of the auxiliary resistance calibration module 21 until the target calibration control signal is output, so that the equivalent resistance value of the auxiliary resistance calibration module 21 reaches the resistance value of the reference resistance. At this time, under the action of the target calibration control signal, the main resistance calibration module 1 adjusts its own equivalent resistance value to match the characteristic impedance of the differential signal transmission circuit.

[0065] The high-speed differential signal impedance matching circuit of the embodiment of the present application includes a main resistance calibration module, a calibration signal circuit and a calibration circuit. The calibration signal circuit includes a secondary resistance calibration module. By considering the characteristic that the characteristic impedance to be matched in the differential signal transmission circuit is relatively small, a calibration mechanism is designed to calibrate the large resistance to proportionally calibrate the small resistance. By comparing the reference voltage output by the calibration signal circuit and the adjustment voltage based on the output of the secondary resistance calibration module, the calibration circuit is triggered to continuously adjust the equivalent resistance value of the secondary resistance calibration module until the target calibration control signal is output so that the equivalent resistance value of the secondary resistance calibration module reaches the resistance value of the reference resistance. At this time, under the action of the target calibration control signal, the equivalent resistance value of the main resistance calibration module can be matched with the characteristic impedance of the differential signal transmission circuit, thereby achieving the effect of automatic calibration of impedance matching and improving the efficiency of impedance matching. The impedance calibration has high accuracy and effectively improves the transmission performance of the high-speed signal transmission system.

[0066] Figure 3 FIG. 2 is a second structural diagram of a high-speed differential signal impedance matching circuit provided in an embodiment of the present application. Figure 3 As shown, the calibration signal circuit 2 further includes a mirror current source 22, a reference resistor 23 and a first switch tube 24;

[0067] One end of the reference resistor 23 and one end of the auxiliary resistor calibration module 21 are both connected to the power supply, and the other end of the reference resistor 23 and the source of the first switch tube 24 are connected to the first input end of the calibration circuit 3, so as to input the reference voltage Vref to the calibration circuit 3 through the first branch where the reference resistor 23 is located;

[0068] The drain of the first switch tube 24 is connected to the first output end of the mirror current source 22, and the gate of the first switch tube 24 is connected to the second output end of the calibration circuit 3;

[0069] The other end of the auxiliary resistor calibration module 21 , the second input end of the calibration circuit 3 and the second output end of the mirror current source 22 are connected in common, so that the second branch where the auxiliary resistor calibration module 21 is located inputs the adjustment voltage Vadj to the calibration circuit 3 .

[0070] Specifically, in the embodiment of the present application, the calibration signal circuit 2 adopts a dual-branch circuit structure, and specifically also includes a mirror current source 22, a reference resistor 23 and a first switch tube 24. Two identical currents provided by the mirror current source 22 flow through the two branches. Among them, the reference resistor 23 can be recorded as Rref, which can be determined in advance according to the equivalent resistance value multiple relationship between the main and auxiliary resistance calibration modules and the size of the characteristic impedance Z0 on the differential transmission line.

[0071] Optionally, in the embodiment of the present application, the first switch tube 24 may be a MOS switch tube, such as an NMOS tube.

[0072] Furthermore, one end of the reference resistor 23 and one end of the auxiliary resistor calibration module 21 are connected to the power supply, the other end of the reference resistor 23 and the source of the first switch tube 24 are connected in common with the first input end of the calibration circuit 3, and the reference voltage Vref can be input to the calibration circuit 3 through the first branch where the reference resistor 23 is located; the other end of the auxiliary resistor calibration module 21, the second input end of the calibration circuit 3 and the second output end of the mirror current source 22 are connected in common, and the adjustment voltage Vadj can be input to the calibration circuit 3 through the second branch where the auxiliary resistor calibration module 21 is located.

[0073] The circuit of the embodiment of the present application constructs a calibration signal circuit by utilizing a secondary resistor calibration module, a mirror current source, a reference resistor and a switch tube, and adopts a dual-branch calibration circuit structure. The branch where the reference resistor is located is used as a reference branch to calibrate the secondary resistor calibration module on the other branch. It can provide a reliable calibration voltage signal for the calibration circuit connected later, which is conducive to realizing automatic calibration of impedance matching and improving the efficiency of impedance matching.

[0074] Continue to refer to Figure 2 As an optional embodiment, the calibration circuit 3 includes a comparator 31, an operational amplifier 32 and a digital calibration module 33;

[0075] The positive input terminal of the comparator 31 is used as the first input terminal of the calibration circuit 3, and the negative input terminal of the comparator 31 is used as the second input terminal of the calibration circuit 3; the output terminal of the digital calibration module 33 is used as the first output terminal of the calibration circuit 3, and the output terminal of the operational amplifier 32 is used as the second output terminal of the calibration circuit 3;

[0076] The positive input terminal of the comparator 31 is connected to the negative input terminal of the operational amplifier 32 ; the output terminal of the comparator 31 is connected to the input terminal of the digital calibration module 33 ; the positive input terminal of the operational amplifier 32 is used to input a reference voltage Vref.

[0077] Specifically, in the embodiment of the present application, the calibration circuit 3 includes a comparator 31, an operational amplifier 32 and a digital calibration module 33, and calibrates the equivalent resistance value of the resistance calibration module by signal comparison.

[0078] More specifically, in the embodiment of the present application, the positive input terminal of the comparator 31 is used as the first input terminal of the calibration circuit 3, and the negative input terminal of the comparator 31 is used as the second input terminal of the calibration circuit 3. In this way, the other end of the reference resistor 23 in the calibration signal circuit 2 and the source of the first switch tube 24 are connected to the positive input terminal of the comparator 31, so that the first branch where the reference resistor 23 is located can input the reference voltage Vref to the positive input terminal of the comparator 31.

[0079] Furthermore, the other end of the auxiliary resistor calibration module 21, the negative input end of the comparator 31 and the second output end of the mirror current source 22 are connected in common. Therefore, the second branch where the auxiliary resistor calibration module 21 is located can input the adjustment voltage Vadj to the negative input end of the comparator 31. After receiving the signals of the reference voltage Vref and the adjustment voltage Vadj, the comparator 31 can compare the reference voltage Vref and the adjustment voltage Vadj for subsequent calibration.

[0080] In an embodiment of the present application, the output end of the operational amplifier 32 serves as the second output end of the calibration circuit 3, is connected to the gate of the first switch tube 24, and the positive input end of the comparator 31 is connected to the negative input end of the operational amplifier 32; the positive input end of the operational amplifier 32 is used to input the reference voltage Vref, so that the virtual short characteristic of the ideal operational amplifier can be utilized, that is, under ideal circumstances, the two input ends of the operational amplifier can be regarded as having the same potential. At this time, the voltage at the point on the first branch connected to the operational amplifier can be maintained at a stable Vref value.

[0081] Furthermore, in an embodiment of the present application, the output end of the comparator 31 is connected to the input end of the digital calibration module 33. The output end of the digital calibration module 33 serves as the first output end of the calibration circuit 3 and is respectively connected to the main resistance calibration module 1 and the auxiliary resistance calibration module 21. The main resistance calibration module 1 and the auxiliary resistance calibration module 21 can calibrate and adjust their own equivalent resistance values ​​under the digital control signal output by the digital calibration module 33.

[0082] The circuit of the embodiment of the present application can realize a digital signal circuit calibration mechanism by constructing a calibration circuit using a comparator, an operational amplifier and a digital calibration module, which is beneficial to further improve the calibration efficiency of impedance matching. At the same time, by adopting a method of cooperating between an analog circuit and a digital calibration circuit, it can reduce the workload of manual testing, reduce the complexity and difficulty of pure analog circuits, and facilitate the realization of more stable, more accurate and lower-cost high-speed signal impedance matching.

[0083] Based on the content of the above embodiment, as an optional embodiment, the reference voltage is provided by a bandgap reference circuit.

[0084] Specifically, the bandgap reference outputs a reference voltage Vref that is independent of temperature and process. In order to generate a constant variable that is independent of the temperature coefficient, it can be assumed that there is a pair of quantities with opposite temperature coefficients in the analog circuit, and the quantities with positive temperature coefficients and negative temperature coefficients are added with different weights to compensate each other and finally obtain a quantity with zero temperature coefficient, that is, two appropriate variables a1 and a2 are selected to make the following equation true:

[0085]

[0086] Furthermore, a constant voltage that is independent of temperature, namely the reference voltage Vref, can be obtained, and its expression can be expressed as:

[0087] V ref =a1V1+a2V2;

[0088] Wherein, V1 represents a voltage parameter that is positively correlated with temperature, and V2 represents a voltage parameter that is negatively correlated with temperature.

[0089] The circuit of the embodiment of the present application uses a reference voltage provided by a bandgap reference circuit to ensure that the provided reference voltage signal is a constant variable that is independent of the temperature coefficient and process, thereby effectively improving the accuracy of high-speed differential signal impedance matching.

[0090] Continue to refer to Figure 3 In the embodiment of the present application, the mirror current source 22 is used to provide two identical currents, wherein one current flows through a first branch and the other current flows through a second branch;

[0091] The operational amplifier 32 is used to provide a reference voltage and clamp the voltage on the first branch to the reference voltage;

[0092] The comparator 31 is used to compare the reference voltage and the adjustment voltage;

[0093] The digital calibration module 33 is used to output a calibration control signal to the auxiliary resistor calibration module 21 according to the comparison result output by the comparator 31 , so as to adjust the first equivalent resistance value.

[0094] Specifically, in an embodiment of the present application, the mirror current source 22 can use a bias circuit mirror to obtain two identical currents, one current flows through the first branch, and the other current flows through the second branch. In this way, a reference current Iref with a size ratio of 1:1 can flow through the reference resistor Rref and the auxiliary resistor calibration module.

[0095] Furthermore, by using the bandgap reference and the operational amplifier 32 to provide a reference voltage, the voltage on the first branch is clamped to a reference voltage of a constant value. In this way, the magnitude of the constant current Iref output by the mirror current source can be determined according to the reference resistor Rref and the reference voltage Vref. The power supply voltage VDD connected to the two branches is the same, such as 3.3V, and the only difference is the resistance in the branch. Therefore, by using the comparator 31 to compare the magnitude of the reference voltage Vref of the first branch where the reference resistor Rref is located and the magnitude of the adjustment voltage Vadj of the second branch where the auxiliary resistor calibration module is located, the magnitude of the equivalent resistance in the two branches can be compared.

[0096] In the embodiment of the present application, the voltages Vref and Vadj of the two branches are compared by a comparator 31. Generally, an ideal comparator can be regarded as a 1-bit analog-to-digital converter. When Vref-Vadj>0, the comparator 31 will output a logic "1"; when Vref-Vadj<0, the comparator 31 will output a logic "0".

[0097] In actual situations, the parameters of the comparator such as DC gain transmission delay, input common mode range, and input offset voltage are different from those in ideal situations. In order to meet the requirements of high precision and low offset voltage and reduce the requirements for response speed, the comparator 31 of the embodiment of the present application can adopt a two-stage amplifier cascade structure, followed by a multi-stage inverter to improve the load driving capability and shape the output signal at the same time.

[0098] Furthermore, in an embodiment of the present application, after the high and low levels of the comparator 31 are output to the digital calibration module 33, the digital calibration module 33 can output a calibration control signal to the secondary resistor calibration module 21 through an algorithm based on the comparison result output by the comparator 31, so as to adjust the first equivalent resistance value, that is, the equivalent resistance value of the secondary resistor calibration module 21, and at the same time, synchronously adjust the equivalent resistance value of the main resistor calibration module 1.

[0099] The circuit of the embodiment of the present application obtains two identical currents by utilizing a mirror current source, and then utilizes a bandgap reference and an operational amplifier to clamp the voltage of the reference branch at a constant value, and then utilizes a comparator to compare the voltages of the two branches, and determines the control signal output by the digital calibration module algorithm through the output high and low levels, and calibrates the resistance value of the positive and secondary resistor calibration modules, which can effectively optimize the response of the impedance matching circuit and make the transmission performance of high-speed differential signals more accurate and efficient.

[0100] Figure 4 is one of the circuit structure diagrams of the resistance calibration module provided in the embodiment of the present application, such as Figure 4 As shown, the main resistance calibration module 1 and the auxiliary resistance calibration module 21 both include multi-way switch branches connected in parallel, and each switch branch includes a second switch tube and a resistor connected in sequence;

[0101] Among them, in the arrangement order of the switch branches, except for the first switch branch, the other multiple switch branches are switch control branches (for the convenience of description, hereinafter referred to as SW branches), and the resistance of each SW branch is twice the resistance of the previous switch branch.

[0102] Specifically, in the embodiment of the present application, the main resistance calibration module 1 and the auxiliary resistance calibration module 21 both adopt a parallel multi-way switch branch structure to facilitate the adjustment and calibration of their own equivalent resistance values. Each switch branch includes a second switch tube and a resistor connected in sequence, wherein the second switch tube can be a MOS switch tube, such as a PMOS tube.

[0103] More specifically, in the embodiments of the present application, each resistance calibration module can be composed of n+1 resistors and PMOS tubes connected in parallel, and in the arrangement order of the switch branches, it includes a first switch branch and n SW branches. Among them, the first switch branch is in the on state; in each SW branch, the source end of the PMOS tube is connected to the power supply VDD, one end of each resistor is connected to the drain end of the PMOS tube, and the other end is connected to the Vadj end output by the second branch. The equivalent resistance value of the resistance calibration module is defined by the parallel value of these resistors. The digital calibration module 33 outputs n binary calibration control signals SW1-SWn to the PMOS switch tubes in the resistance calibration module, which respectively control the on and off of the n SW branches, thereby controlling the connection of each resistor to the resistance network.

[0104] In the embodiment of the present application, the resistance is calibrated by binary division, and the resistance of each SW branch is twice the resistance of the previous switch branch, that is, the resistance array is doubled. For example, the resistance of the first switch branch is R, the resistance of the first SW branch is 2R, and the resistance of the second SW branch is 4R.

[0105] Here, when the i-th branch resistor in each resistance calibration module is connected in parallel with the branch where the resistor R is located, the equivalent resistance value r of the resistance calibration module can be expressed as:

[0106]

[0107] It can be understood that the parallel connection of the resistor R with the first few branches is equivalent to coarse adjustment, and the parallel connection with the last few branches is equivalent to fine adjustment. The resistance calibration ratio between adjacent parallel branches is about 1 / 2, which conforms to the binary relationship.

[0108] It should be noted that in the embodiments of the present application, the resistor R is not only connected in parallel with each branch resistor individually, but can also be connected in parallel with different branches at the same time to expand the calibration amount. Therefore, by selecting a suitable R value, the resistance calibration range can meet the required calibration range.

[0109] The circuit of the embodiment of the present application utilizes multi-way switch branches in parallel, and each switch branch is composed of a switch tube in series with a resistor, so as to construct a main and auxiliary resistor calibration module. By selecting different switch branches in parallel, automatic calibration of the equivalent resistance values ​​of the main and auxiliary resistor calibration modules is achieved. The resistance calibration range is large, which can effectively improve the calibration accuracy of high-speed differential signal impedance matching.

[0110] Figure 5 FIG. 2 is a second circuit structure diagram of a resistance calibration module provided in an embodiment of the present application. Figure 5 As shown, each SW branch includes an inverter, the output end of the inverter is connected to the gate of the second switch tube, and the input end of the inverter is used to input the calibration control signal output by the calibration circuit.

[0111] Specifically, in the embodiment of the present application, the gate of the PMOS tube in each SW branch is connected to an inverter, and the n-way binary calibration control signal SW1-SWn output by the digital calibration module 33 is input to the inverter. In this way, by introducing an inverter before the PMOS tube, the inverter can be used as a buffer link to enhance the stability of the control signal or adjust the phase of the signal, so as to achieve more stable and accurate high-speed signal impedance matching.

[0112] Based on the content of the above embodiment, as an optional embodiment, the calibration circuit 3 is specifically used for:

[0113] When the adjustment voltage is not greater than the reference voltage, the auxiliary resistor calibration module 21 is controlled to be incorporated into the next SW branch of the most recently incorporated SW branch to adjust the first equivalent resistance value and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistor.

[0114] Specifically, in an embodiment of the present application, after the calibration circuit 3 inputs the adjustment voltage Vadj and the reference voltage Vref, if the calibration circuit 3 is constructed using the above-mentioned circuit composed of the comparator 31, the operational amplifier 32 and the digital calibration module 33, the comparator 31 outputs high and low levels, and then the digital calibration module 33 outputs n binary calibration control signals for calibration.

[0115] Among them, the calibration logic is related to the result output by the comparator 31. During the calibration process, the comparator 31 compares the values ​​of the adjustment voltage Vadj and the reference voltage Vref. If the adjustment voltage Vadj is not greater than the reference voltage Vref, the two are not equal. If the adjustment voltage Vadj is not greater than the reference voltage Vref, the comparator 31 outputs a high level. At this time, it means that the equivalent resistance value of the resistance calibration module is greater than the resistance value of the reference resistance Rref, indicating that the calibration is insufficient.

[0116] It should be noted that under-calibration and over-calibration can be compensated by calibrating the resistor parallel relationship of the resistor calibration module through the control signal of the calibration logic. Under-calibration requires continuing to connect more branches in parallel to increase the calibration amount, while over-calibration requires withdrawing some parallel branches to reduce the calibration amount.

[0117] In addition, it should be noted that before starting the calibration, all control signals on SW1-SWn need to be reset to zero (the specific number of paths used determines the calibration accuracy), and then all registers in the digital calibration module 33 are reset to clear the random data in the registers to avoid unknown errors.

[0118] Furthermore, after receiving the high level, the digital calibration module 33 outputs the corresponding calibration control signal according to the algorithm, controls the conduction state of the switch branch inside the auxiliary resistor calibration module 21, and makes the auxiliary resistor calibration module 21 merge into the next SW branch of the SW branch in sequence. For example, the switch branch currently merged by the auxiliary resistor calibration module 21 includes the first switch branch and the SW branch controlled by the signal SW1. It can be determined that the latest SW branch merged is the SW branch controlled by the signal SW1. At this time, the SW branch controlled by the signal SW2 is merged in sequence. Therefore, the adjustment of the equivalent resistance value of the auxiliary resistor calibration module 21 is realized, and then the adjustment voltage Vadj output by the second branch is changed, and the next round of comparison is entered in a cycle, and the above calibration process is repeated.

[0119] Through the above-mentioned iterative comparison, it is continuously determined whether the adjustment voltage Vadj is equal to the reference voltage Vref until it is determined that the two are equal, and then it is determined that the equivalent resistance value of the auxiliary resistor calibration module 21 reaches the resistance value of the reference resistor, so that the target calibration control signal output by the digital calibration module 33 at this time controls the equivalent resistance value of the main resistor calibration module 1 to match the characteristic impedance of the differential signal transmission circuit.

[0120] The circuit of the embodiment of the present application, when it is determined that the adjustment voltage is not greater than the reference voltage, controls the auxiliary resistor calibration module to be sequentially integrated into a SW branch, and gradually calibrates the equivalent resistance value of the auxiliary resistor calibration module. This can effectively implement a calibration mechanism for the resistor calibration module in an insufficient calibration scenario with high calibration accuracy.

[0121] Based on the content of the above embodiment, as an optional embodiment, the calibration circuit 3 is further used for:

[0122] When the adjustment voltage is greater than the reference voltage, the auxiliary resistor calibration module 21 is controlled to cancel the most recently incorporated SW branch and incorporate the next SW branch of the most recently incorporated SW branch to adjust the first equivalent resistance value and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistance.

[0123] Specifically, in an embodiment of the present application, after inputting the adjustment voltage Vadj and the reference voltage Vref, the calibration circuit 3 outputs high and low levels through its internal comparator 31, and controls the digital calibration module 33 to output n binary calibration control signals to calibrate the equivalent resistance value of the auxiliary resistor calibration module 21.

[0124] During the calibration process, the comparator 31 compares the values ​​of the adjustment voltage Vadj and the reference voltage Vref. If the adjustment voltage Vadj is greater than the reference voltage Vref and the two are not equal, the comparator 31 outputs a low level, which means that the equivalent resistance value of the resistance calibration module is less than the resistance value of the reference resistance Rref, indicating over-calibration.

[0125] Furthermore, after receiving the low level, the digital calibration module 33 outputs the corresponding calibration control signal according to the algorithm, controls the conduction state of the switch branch inside the auxiliary resistance calibration module 21, and makes the auxiliary resistance calibration module 21 cancel the incorporation of the latest SW branch, and incorporate the next SW branch of the latest SW branch. For example, the switch branch currently incorporated by the auxiliary resistance calibration module 21 includes the first switch branch and the SW branch under the control of the signal SW1, and the latest SW branch is the SW branch under the control of the signal SW1. At this time, the SW branch under the control of the signal SW1 will be canceled, and the SW branch under the control of the signal SW2 will be incorporated. In this way, the equivalent resistance value of the auxiliary resistance calibration module 21 is adjusted, and then the adjustment voltage Vadj output by the second branch is changed, and then the next round of comparison is cycled into, and the above calibration process is repeated.

[0126] Through the above-mentioned iterative comparison, it is continuously determined whether the adjustment voltage Vadj is equal to the reference voltage Vref until it is determined that the two are equal, and then it can be determined that the equivalent resistance value of the auxiliary resistor calibration module 21 has reached the resistance value of the reference resistor. At this time, the digital calibration module 33 outputs the target calibration control signal to control the equivalent resistance value of the main resistor calibration module 1 to match the characteristic impedance of the differential signal transmission circuit.

[0127] The circuit of the embodiment of the present application, when it is determined that the adjustment voltage is greater than the reference voltage, controls the auxiliary resistor calibration module to cancel the most recently incorporated SW branch and selects to incorporate the next SW branch to gradually calibrate the equivalent resistance value of the auxiliary resistor calibration module. This can effectively implement the calibration mechanism of the resistor calibration module in the over-calibration scenario with high calibration accuracy.

[0128] Figure 6 is a flow chart of a method for calibrating a primary and secondary resistor calibration module by a calibration circuit provided in an embodiment of the present application, such as Figure 6 As shown, in the embodiment of the present application, the calibration circuit is first initialized, and all SW control signals need to be set to zero, that is, all n control signals of SW1-SWn are set to zero, and then all registers in the digital calibration module are reset to clear the random data in the registers.

[0129] Further, step S41 is executed to perform subsequent calibration control using the digital calibration module. The calibration control signal output by the digital calibration module is controlled by the high and low levels output by the comparator in the calibration circuit to adjust the incorporation of the SW branch in the positive and auxiliary resistor calibration modules and calibrate the equivalent resistance values ​​of the positive and auxiliary resistor calibration modules.

[0130] Execute step S42 to change the number of parallel resistors in the auxiliary resistor calibration module and adjust the equivalent resistance value. The overall calibration logic is: after the current SW branch is connected, that is, after the latest SW branch is incorporated, if the comparator output is high, it means that the calibration is insufficient, and the next level SW branch is continued to be incorporated for calibration; if the comparator output is low after the current SW branch is connected, it means that the calibration is excessive, and the SW branch control signal needs to be reset, the incorporation of the current SW branch is canceled, and the incorporation of the next level SW branch is controlled at the same time.

[0131] Among them, in the specific calibration process, the comparator compares the values ​​of Vref and Vadj. If Vadj is not greater than Vref, the comparator output is a high level, which means that the equivalent resistance of the resistance calibration module is greater than Rref, indicating insufficient calibration; if Vadj is greater than Vref, the comparator output is a low level, which means that the equivalent resistance of the calibration resistance module is less than the reference resistance Rref, indicating excessive calibration.

[0132] Execute step S43, use the binary method to gradually calibrate the equivalent resistance value of the auxiliary resistor calibration module. Use the calibration logic in step S42 to sequentially control the n SW branches until the equivalent resistance value of the auxiliary resistor calibration module is close to the resistance value of the reference resistor Rref.

[0133] Execute step S44. Initially, the equivalent resistance value of the auxiliary resistance calibration module is much larger than the equivalent resistance value of the main resistance calibration module, and is in a target multiple relationship. The n-way binary control bits of the positive and auxiliary resistance calibration modules are the same. Using the auxiliary resistance calibration module to correct the main resistance calibration module as a matching resistor has a larger calibration range, and the calibration accuracy and speed will also be higher. Therefore, after determining the specific SW parameters of the target calibration control signal, this control signal is output to the main resistance calibration module so that its equivalent resistance value is close to the characteristic impedance Z0 on the differential signal transmission line.

[0134] The impedance matching method provided by the present invention is described below. The impedance matching method described below and the high-speed differential signal impedance matching circuit described above can be referred to each other.

[0135] Figure 7 is a flow chart of an impedance matching method provided in an embodiment of the present application, which can be applied to any of the above-mentioned high-speed differential signal impedance matching circuits, such as Figure 7 As shown, the impedance matching method includes:

[0136] Step S1, inputting a reference voltage and an adjustment voltage into a calibration circuit using a calibration signal circuit;

[0137] Step S2, using the calibration circuit, compares the reference voltage and the adjustment voltage, and continuously adjusts the first equivalent resistance value of the secondary resistor calibration module according to the comparison result, until the target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistor, and the second equivalent resistance value of the main resistor calibration module matches the characteristic impedance of the differential signal transmission circuit.

[0138] It can be understood that the detailed implementation of each of the above steps can be found in the introduction of the above high-speed differential signal impedance matching circuit embodiment, which will not be elaborated here.

[0139] It should be understood that the above method is applied to the embodiment of the above high-speed differential signal impedance matching circuit, and its implementation principle and technical effect are similar to the description in the above circuit embodiment. The implementation process of the impedance matching method can refer to the corresponding process in the above circuit embodiment, which will not be repeated here.

[0140] The impedance matching method of the high-speed differential signal impedance matching circuit of the embodiment of the present application designs a calibration mechanism for proportionally calibrating small resistors by calibrating large resistors by considering the characteristic that the characteristic impedance to be matched in the differential signal transmission circuit is relatively small. The calibration circuit is triggered to continuously adjust the equivalent resistance value of the secondary resistor calibration module by comparing the reference voltage output by the calibration signal circuit and the adjustment voltage based on the output of the secondary resistor calibration module until the target calibration control signal is output so that the equivalent resistance value of the secondary resistor calibration module reaches the resistance value of the reference resistor. At this time, under the action of the target calibration control signal, the equivalent resistance value of the main resistor calibration module can be matched with the characteristic impedance of the differential signal transmission circuit, thereby achieving the effect of automatic calibration of impedance matching, improving the efficiency of impedance matching, and having high impedance calibration accuracy, which effectively improves the transmission performance of the high-speed signal transmission system.

[0141] It should be understood that the various numerical numbers involved in the embodiments of the present application are only used for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0142] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

[0143] It should be understood that expressions such as "including" and "may include" that may be used in the present application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0144] In addition, in the embodiments of the present application, the mathematical concepts mentioned, such as symmetry, equality, parallelism, and perpendicularity, are all limited to the current technological level, rather than being absolutely strict definitions in the mathematical sense, and a small amount of deviation is allowed, such as approximately symmetry, approximately equality, approximately parallelism, and approximately perpendicularity.

[0145] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A high-speed differential signal impedance matching circuit, applied to a differential signal transmission circuit, characterized in that: include: A main resistance calibration module, a calibration signal circuit and a calibration circuit; the calibration signal circuit includes a secondary resistance calibration module; The first output end of the calibration circuit is connected to the main resistance calibration module and the auxiliary resistance calibration module respectively; the calibration signal circuit is connected to the calibration circuit; The calibration signal circuit is used to input a reference voltage and a regulation voltage to the calibration circuit; The regulating voltage is determined based on a first equivalent resistance value of the secondary resistance calibration module; The calibration circuit is used to adjust the first equivalent resistance value based on the reference voltage and the adjustment voltage until a target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistance, and the second equivalent resistance value of the main resistance calibration module matches the characteristic impedance of the differential signal transmission circuit; the first equivalent resistance value is equal to the target multiple of the second equivalent resistance value.

2. The high-speed differential signal impedance matching circuit according to claim 1, characterized in that: The calibration signal circuit also includes a mirror current source, a reference resistor and a first switch tube; One end of the reference resistor and one end of the auxiliary resistor calibration module are both connected to a power supply, and the other end of the reference resistor, the source of the first switch tube and the first input end of the calibration circuit are connected in common, so that the first branch where the reference resistor is located inputs the reference voltage to the calibration circuit; The drain of the first switch tube is connected to the first output end of the mirror current source, and the gate of the first switch tube is connected to the second output end of the calibration circuit; The other end of the secondary resistor calibration module, the second input end of the calibration circuit and the second output end of the mirror current source are connected in common, so that the second branch where the secondary resistor calibration module is located inputs the adjustment voltage to the calibration circuit.

3. The high-speed differential signal impedance matching circuit according to claim 2, characterized in that: The calibration circuit includes a comparator, an operational amplifier and a digital calibration module; The positive input terminal of the comparator serves as the first input terminal of the calibration circuit, and the negative input terminal of the comparator serves as the second input terminal of the calibration circuit; the output terminal of the digital calibration module serves as the first output terminal of the calibration circuit, and the output terminal of the operational amplifier serves as the second output terminal of the calibration circuit; The positive input terminal of the comparator is connected to the negative input terminal of the operational amplifier; the output terminal of the comparator is connected to the input terminal of the digital calibration module; the positive input terminal of the operational amplifier is used to input a reference voltage.

4. The high-speed differential signal impedance matching circuit according to claim 3, characterized in that: The mirror current source is used to provide two identical currents, wherein one current flows through the first branch and the other current flows through the second branch; The operational amplifier is used to provide the reference voltage and clamp the voltage on the first branch to the reference voltage; The comparator is used to compare the reference voltage with the adjustment voltage; The digital calibration module is used to output a calibration control signal to the auxiliary resistance calibration module according to a comparison result output by the comparator, so as to adjust the first equivalent resistance value.

5. The high-speed differential signal impedance matching circuit according to any one of claims 1 to 4, characterized in that: The reference voltage is provided by a bandgap reference circuit.

6. The high-speed differential signal impedance matching circuit according to any one of claims 1 to 4, characterized in that: The main resistance calibration module and the auxiliary resistance calibration module both include multi-way switch branches connected in parallel, and each of the switch branches includes a second switch tube and a resistor connected in sequence; Among them, in the arrangement order of the switch branches, except the first switch branch, the other switch branches are switch control branches, and the resistance of each switch control branch is twice the resistance of the previous switch branch.

7. The high-speed differential signal impedance matching circuit according to claim 6, characterized in that: Each of the switch control branches includes an inverter, the output end of the inverter is connected to the gate of the second switch tube, and the input end of the inverter is used to input the calibration control signal output by the calibration circuit.

8. The high-speed differential signal impedance matching circuit according to claim 7, characterized in that: The calibration circuit is specifically used for: When the adjustment voltage is not greater than the reference voltage, the secondary resistor calibration module is controlled to be incorporated into the next switch control branch that is most recently incorporated into the switch control branch to adjust the first equivalent resistance value and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistor.

9. The high-speed differential signal impedance matching circuit according to claim 8, characterized in that: The calibration circuit is also specifically used for: When the adjustment voltage is greater than the reference voltage, the secondary resistor calibration module is controlled to cancel the incorporation of the most recently incorporated switch control branch, and to incorporate the next switch control branch of the most recently incorporated switch control branch to adjust the first equivalent resistance value, and change the adjustment voltage until it is determined that the first equivalent resistance value reaches the resistance value of the reference resistance.

10. An impedance matching method applied to the high-speed differential signal impedance matching circuit according to any one of claims 1 to 9, characterized in that: include: inputting a reference voltage and an adjustment voltage into the calibration circuit using the calibration signal circuit; The calibration circuit is used to compare the reference voltage and the adjustment voltage, and the first equivalent resistance value of the secondary resistor calibration module is continuously adjusted according to the comparison result until a target calibration control signal is output, so that the first equivalent resistance value reaches the resistance value of the reference resistor, and the second equivalent resistance value of the main resistor calibration module matches the characteristic impedance of the differential signal transmission circuit.

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