Line driver impedance calibration overvoltage protection circuit and method

Abstract

The application relates to a line driver impedance calibration overvoltage protection circuit and method, which is applied to an Ethernet and comprises a first impedance calibration circuit and an overvoltage protection circuit. The first impedance calibration circuit comprises a plurality of first transmission gates, two ends of each first transmission gate are connected with a first resistor and a second resistor respectively, and the first transmission gate can be controlled to be turned on or turned off to adjust the impedance between the line driver and the first connection end to a preset value. The overvoltage protection circuit is used for detecting the amplitude of the opposite end signal received by the hybrid circuit, comparing the amplitude of the opposite end signal with a predetermined threshold value, outputting a comparison signal, and controlling the amplitude of the local end signal sent by the line driver according to the comparison signal. The application can realize impedance calibration, the transmission gate works at the intermediate voltage, the voltage interval range is smaller, the overvoltage of the transmission gate is protected, the tolerance of the reliability of the Ethernet is better, the amplitude of the local end is limited, and then the overvoltage protection of the impedance calibration is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of impedance calibration and overvoltage protection, in particular to a line driver impedance calibration overvoltage protection circuit and method. BACKGROUND

[0002] Line driver is divided into voltage type line driver and current type line driver, which is a kind of digital modulation and demodulation technology based on high-speed digital signal processing technology, and is also the key to the excellent performance of modern communication transmission. However, in order to send the modulated signal to the twisted pair without distortion and meet the required output power, a high-performance analog interface circuit is needed to process the signal first. The analog interface circuit mainly consists of line driver circuit, signal transceiver circuit and hybrid circuit.

[0003] The existing 28 / 14nm process chip has only 1.8V device, while the Ethernet protocol specifies that the transmission voltage amplitude is 2V Vpp, so the overvoltage design needs to work with 3.3V power supply. The overvoltage design in the prior art usually uses CMOS tube plus protection voltage, but the voltage amplitude of the signal from the opposite end is superimposed during transmission, and the voltage amplitude output to the transmission line is large, and the reliability is low. The reliability requirement of vehicle Ethernet is high, and the existing line driver cannot meet the requirements of vehicle Ethernet. Therefore, in view of the above problems, it is urgent to design a line driver impedance calibration overvoltage protection circuit and method to meet the actual use needs. SUMMARY

[0004] In view of the above problems, the present application provides a line driver impedance calibration overvoltage protection circuit and method.

[0005] The technical problem solved by the present application can be realized by the following technical scheme:

[0006] A line driver impedance calibration overvoltage protection circuit applied to Ethernet, comprising:

[0007] A first impedance calibration circuit connected between a line driver and a first connection end of a hybrid circuit, the first impedance calibration circuit comprising:

[0008] A plurality of first transmission gates, each first transmission gate having a first resistor and a second resistor connected to both ends thereof, and each first transmission gate being controllable to be turned on or turned off under the action of a switch control signal to adjust the impedance between the line driver and the first connection end to a preset value;

[0009] An overvoltage protection circuit connected to the line driver and the hybrid circuit respectively, the overvoltage protection circuit comprising:

[0010] an amplitude detection circuit, configured to detect the amplitude of a peer signal received by the hybrid circuit;

[0011] a digital control circuit, configured to compare the amplitude of the opposite-end signal with a predetermined threshold value and output a comparison signal;

[0012] An amplitude control circuit is used to control the amplitude of the local end signal sent by the line driver according to the comparison signal.

[0013] The above-mentioned line driver impedance calibration overvoltage protection circuit further includes: a second impedance calibration circuit connected between the line driver and the second connection terminal of the hybrid circuit, the second impedance calibration circuit including:

[0014] and a plurality of second transmission gates, each of which has two ends connected to a third resistor and a fourth resistor, respectively. Each of the second transmission gates can be controlled to be turned on or off under the action of the switch control signal to adjust the impedance between the line driver and the second connection end to the preset value.

[0015] In the above-mentioned line driver impedance calibration overvoltage protection circuit, when the amplitude of the opposite-end signal is greater than the predetermined threshold, the amplitude control circuit controls the amplitude of the local-end signal to be sent to be halved;

[0016] When the amplitude of the opposite-end signal is less than or equal to the predetermined threshold, the local-end signal is sent according to its original amplitude.

[0017] The above-mentioned line driver impedance calibration overvoltage protection circuit further includes:

[0018] A first voltage divider circuit, configured to output a first intermediate voltage;

[0019] A second voltage divider circuit, configured to output a second intermediate voltage;

[0020] a level conversion unit, wherein the input end of the level conversion unit is respectively connected to the first voltage divider circuit and the second voltage divider circuit, and the output end of the level conversion unit is respectively connected to each of the first transmission gates, and is configured to switch between the first intermediate voltage and the second intermediate voltage to output the switch control signal, thereby controlling the branches between the line driver and the first connection end, where the branches of the first transmission gates are located, to be respectively turned on or off.

[0021] In the above-mentioned line driver impedance calibration overvoltage protection circuit, the first transmission gate includes:

[0022] A first PMOS transistor and a first NMOS transistor having source and drain electrodes connected in parallel;

[0023] The gate of the first PMOS tube is connected with the switch control signal, the drain of the first PMOS tube is connected with the first resistor, and the source of the first PMOS tube is connected with the second resistor.

[0024] The gate of the first NMOS tube is connected with the inverse phase signal of the switch control signal.

[0025] The line driver impedance calibration overvoltage protection circuit further comprises:

[0026] The first voltage dividing circuit is used for outputting a first intermediate voltage.

[0027] The second voltage dividing circuit is used for outputting a second intermediate voltage.

[0028] The level conversion unit is connected with the first voltage dividing circuit and the second voltage dividing circuit respectively at the input end, and is connected with each second transmission gate at the output end, and is used for switching between the first intermediate voltage and the second intermediate voltage to output the switch control signal, so as to control each branch of the second transmission gate between the line driver and the second connection end to be turned on or turned off.

[0029] The line driver impedance calibration overvoltage protection circuit further comprises:

[0030] The second PMOS tube and the second NMOS tube are connected in parallel between the source and the drain.

[0031] The gate of the second PMOS tube is connected with the switch control signal, the drain of the second PMOS tube is connected with the third resistor, and the source of the second PMOS tube is connected with the fourth resistor.

[0032] The gate of the second NMOS tube is connected with the inverse phase signal of the switch control signal.

[0033] The line driver impedance calibration overvoltage protection circuit further comprises:

[0034] The line driver impedance calibration overvoltage protection method is applied to the line driver impedance calibration overvoltage protection circuit, and the method comprises:

[0035] Each first transmission gate can be turned on or turned off under the action of a switch control signal to adjust the impedance between the line driver and the first connection end of the hybrid circuit to a preset value; and / or

[0036] Under the action of the switch control signal, each of the second transmission gates can be controlled to be turned on or off to adjust the impedance between the line driver and the second connection terminal of the hybrid circuit to the preset value;

[0037] The method further includes: detecting the amplitude of the opposite end signal received by the hybrid circuit;

[0038] comparing the detected amplitude of the opposite-end signal with a predetermined threshold and outputting a comparison signal;

[0039] The amplitude of the local end signal sent by the line driver is controlled according to the comparison signal.

[0040] The above-mentioned line driver impedance calibration overvoltage protection method further includes:

[0041] When the amplitude of the opposite-end signal is greater than the predetermined threshold, controlling the amplitude of the local-end signal to be sent to be halved;

[0042] When the amplitude of the opposite-end signal is less than or equal to the predetermined threshold, the local-end signal is sent according to its original amplitude.

[0043] The beneficial effects of the technical solution of the present invention are as follows: the impedance between the line driver and the first and second connection terminals of the hybrid circuit is limited to a preset value through a transmission gate, thereby achieving impedance calibration; the transmission gate operates at an intermediate voltage with a smaller operating voltage range to protect it from overvoltage, thereby improving the tolerance for Ethernet reliability; and by detecting the sending amplitude of the other end, the sending amplitude of the local end is limited according to the sending amplitude of the other end, thereby achieving overvoltage protection for impedance calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a structural block diagram of the line driver impedance calibration overvoltage protection circuit in the present invention;

[0045] Figure 2 1 is a circuit diagram of a line driver impedance calibration overvoltage protection circuit in the present invention;

[0046] Figure 3 This is a circuit diagram of a preferred embodiment of the present invention;

[0047] Figure 4 is a circuit diagram of a first transmission gate in the present invention;

[0048] Figure 5 is a circuit diagram of the second transmission gate in the present invention;

[0049] Figure 6 It is a schematic diagram of the overpressure protection process in the present invention. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0053] The embodiments of the present invention can be applied to both single-ended and differential control. For example, if a first impedance calibration circuit is provided only between the line driver 1 and the first connection terminal of the hybrid circuit, or a second impedance calibration circuit is provided only between the line driver 1 and the second connection terminal of the hybrid circuit 8, single-ended control is achieved. If a first impedance calibration circuit is provided between the line driver 1 and the first connection terminal of the hybrid circuit 8, and a second impedance calibration circuit is provided between the line driver 1 and the second connection terminal of the hybrid circuit 8, differential control is achieved.

[0054] Example 1

[0055] Reference Figures 1-2 An embodiment of the present invention provides a line driver 1 impedance calibration overvoltage protection circuit, applied to Ethernet, comprising:

[0056] A first impedance calibration circuit is connected between a line driver 1 and a first connection terminal of a hybrid circuit 8. The first impedance calibration circuit includes:

[0057] Several first transmission gates (TG 11 …TG 1i ), each first transmission gate (TG 11 …TG 1i ) are connected to a first resistor (R 11 …R 1i ) and a second resistor (R 21 …R 2i ), each first transmission gate (TG 11 …TG 1i ) can be controlled to be turned on or off under the action of a switch control signal to adjust the impedance between the line driver 1 and the first connection end to a preset value;

[0058] An overvoltage protection circuit is connected to the line driver 1 and the hybrid circuit 8, and the overvoltage protection circuit includes:

[0059] an amplitude detection circuit, used to detect the amplitude of the opposite end signal received by the hybrid circuit 8;

[0060] A digital control circuit is used to compare the amplitude of the opposite end signal with a predetermined threshold value and output a comparison signal;

[0061] The amplitude control circuit is used to control the amplitude of the local end signal sent by the line driver 1 according to the comparison signal.

[0062] Specifically, the embodiment of the present invention includes a line driver 1 for driving a network line with a characteristic impedance of 50 ohms, a plurality of first resistance branches connected between a first connection terminal and the line driver 1, each first resistance branch including a first transmission gate (TG 11 …TG 1i ), the first resistor (R 11 …R 1i ) and the second resistor (R 21 …R 2i ); by detecting the parallel impedance deviation of the first resistance branches connected between the first connection terminal and the line driver 1, the number of connected first resistance branches is controlled according to the deviation to adjust the impedance between the line driver 1 and the first connection terminal to a preset value. Preferably, the total resistance of all the connected first resistance branches after being connected in parallel is 50 ohms.

[0063] Because the impedance calibration circuit uses 1.8V components, and the Ethernet protocol specifies a 2V Vpp amplitude for transmitted signals, the amplitude of the signal can reach 2V Vpp for single-ended transmission and 4V Vpp for differential transmission after adding the amplitude of the peer signal. Therefore, an overvoltage design is necessary. To mitigate the effects of the overvoltage design, the present invention also includes an overvoltage protection circuit. This circuit detects the amplitude of the peer signal received by hybrid circuit 8, compares the detected peer signal amplitude with a predetermined threshold, outputs a comparison signal, and controls the amplitude of the local signal transmitted by line driver 1 based on the comparison signal, thereby limiting the transmitted amplitude of the local signal.

[0064] The embodiment of the present invention uses 1.8V devices to not only achieve impedance calibration, but also has a smaller operating voltage range and better tolerance for the reliability of in-vehicle Ethernet; and by detecting the sending amplitude of the other end, the sending amplitude of the local end is limited according to the sending amplitude of the other end, thereby achieving calibrated overvoltage protection.

[0065] As a preferred embodiment, the present invention further includes: a second impedance calibration circuit connected between the line driver 1 and the second connection terminal of the hybrid circuit 8, the second impedance calibration circuit including:

[0066] Several second transmission gates (TG 21 …TG 2i), each second transmission gate (TG 21 …TG 2i ) are connected to a third resistor (R 31 …R 3i ) and a fourth resistor (R 41 …R 5i ), each second transmission gate (TG 21 …TG 2i ) can be controlled to be turned on or off under the action of the switch control signal to adjust the impedance between the line driver 1 and the second connection end to a preset value.

[0067] Specifically, the embodiment of the present invention further includes a plurality of second resistance branches connected between the second connection terminal and the line driver 1, each second resistance branch including a second transmission gate (TG 21 …TG 2i ), the third resistor (R 31 …R 3i ) and the fourth resistor (R 41 …R 5i Similarly, by detecting the deviation of the parallel impedance of the second resistance branches connected between the second connection terminal and the line driver 1, the number of connected second resistance branches is controlled according to the deviation to adjust the impedance between the line driver 1 and the second connection terminal to a preset value. Preferably, the total resistance of all the connected second resistance branches connected in parallel is 50 ohms.

[0068] As a preferred embodiment, when the amplitude of the opposite-end signal is greater than a predetermined threshold, the amplitude control circuit controls the amplitude of the local-end signal to be sent to be halved;

[0069] When the amplitude of the opposite-end signal is less than or equal to a predetermined threshold, the local-end signal is sent according to its original amplitude.

[0070] Specifically, in the embodiment of the present invention, the amplitude detection circuit detects the peer-end transmission amplitude (i.e., the amplitude of the peer-end transmission signal) of the peer-end hybrid circuit 8 via the analog-to-digital converter 5. When the peer-end transmission amplitude has a large swing, i.e., the amplitude of the peer-end transmission signal exceeds a predetermined threshold, the amplitude control circuit limits the amplitude of the local transmission signal via the digital-to-analog converter 4, thereby reducing the voltage amplitude of the local transmission signal. Preferably, the specific value of the predetermined threshold can be determined based on actual application.

[0071] Furthermore, in order to avoid overvoltage after the transmission amplitudes of the opposite end and the local end signals are superimposed, the local end transmission amplitude is reduced by the digital-to-analog converter 4 and then sent to the opposite end mixing circuit 8. In this embodiment, the local end transmission amplitude is reduced to half of the original amplitude.

[0072] Furthermore, a preset limiting strategy may be set, and the digital-to-analog converter 4 controls the local transmission amplitude according to the preset limiting strategy. The preset limiting strategy specifically includes:

[0073] Vt=Vi*A;

[0074] Wherein, Vt represents the local transmission amplitude after the digital-to-analog converter 4 is controlled based on an amplitude control signal;

[0075] Vi represents the original sending amplitude of the local end;

[0076] A represents the limiting coefficient.

[0077] If the amplitude sent by the other end is a large swing, then A is less than 1, and in a preferred embodiment, A=0.5;

[0078] If the amplitude sent by the other end is a small swing, A=1.

[0079] As a preferred embodiment, wherein Figure 3 As shown, it also includes:

[0080] A first voltage divider circuit 71 is configured to output a first intermediate voltage;

[0081] A second voltage divider circuit 72, configured to output a second intermediate voltage;

[0082] The level conversion unit 6, the input end of the level conversion unit is connected to the first voltage divider circuit 71 and the second voltage divider circuit 72, and the output end of the level conversion unit is connected to each first transmission gate (TG 11 …TG 1i ), used to switch between the first intermediate voltage and the second intermediate voltage to output a switch control signal, thereby controlling each first transmission gate (TG) between the line driver 1 and the first connection terminal 11 …TG 1i ) are respectively turned on or off. Preferably, in the embodiment of the present invention, an intermediate voltage is used to trigger the first transmission gate and the second transmission gate to protect the PMOS and NMOS devices constituting the transmission gate from overvoltage. The specific value of the intermediate voltage is determined according to the actual circuit design.

[0083] Specifically, in this embodiment, a plurality of level conversion units 6 may be provided, and the plurality of level conversion units 6 are respectively connected to a corresponding transmission gate (including the first transmission gate and the second transmission gate).

[0084] The level conversion unit 6 is used to switch between the first intermediate voltage and the second intermediate voltage to output a control signal to control the corresponding connected transmission gate to switch between the on state and the off state, thereby adjusting the resistance of the resistors on both sides to a preset value.

[0085] Furthermore, the first voltage divider circuit 71 outputs a first intermediate voltage by resistor voltage division; the second voltage divider circuit 72 outputs a second intermediate voltage by resistor voltage division, so that the transmission gate operates between the first intermediate voltage and the second intermediate voltage. The operating voltage range between the first intermediate voltage and the second intermediate voltage is smaller, and when applied to in-vehicle Ethernet, it has better tolerance for reliability.

[0086] As a preferred embodiment, wherein Figure 4 As shown, the first transmission gate (TG 11 …TG 1i )include:

[0087] A first PMOS transistor MP1 and a first NMOS transistor MN1 having their sources and drains connected in parallel;

[0088] The gate of the first PMOS transistor MP1 is connected to the control signal, and the drain of the first PMOS transistor MP1 is connected to the first resistor (R 11 …R 1i ), the source of the first PMOS tube MP1 is connected to the second resistor (R 21 …R 2i );

[0089] The gate of the first NMOS transistor MN1 is connected to the inverted signal of the switch control signal.

[0090] As a preferred embodiment, wherein Figure 5 As shown, the second transmission gate (TG 21 …TG 2i )include:

[0091] A second PMOS transistor MP2 and a second NMOS transistor MN2 with their source and drain connected in parallel;

[0092] The gate of the second PMOS transistor MP2 is connected to the control signal, the drain of the second PMOS transistor MP2 is connected to the third resistor R3, and the source of the second PMOS transistor MP2 is connected to the fourth resistor R4;

[0093] The gate of the second NMOS transistor MN2 is connected to the inverted signal of the switch control signal.

[0094] As a preferred embodiment, the line driver 1 is a voltage-type line driver 1 .

[0095] The line driver 1 of the present invention is an impedance calibration overvoltage protection circuit, and the line driver 1 is a voltage type line driver 1.

[0096] In the above preferred embodiment, a transformer or common-mode conjugate coil 9 is connected between the first connection end and the second connection end, the transformer or common-mode conjugate coil 9 is connected to the hybrid circuit 8, and a resistor is also connected in parallel at both ends of the transformer or common-mode conjugate coil 9, and the resistance of the resistor is 100 ohm.

[0097] Example 2

[0098] The present invention further provides a line driver 1 impedance calibration overvoltage protection method, characterized in that it is applied to a line driver 1 impedance calibration overvoltage protection circuit as described above, and the method includes:

[0099] Under the action of a switch control signal, each first transmission gate (TG 11 …TG 1i ) to adjust the impedance between the line driver 1 and the first connection terminal of the hybrid circuit 8 to a preset value; and / or

[0100] Under the action of the switch control signal, each second transmission gate (TG 21 …TG 2i ) to adjust the impedance between the line driver 1 and the second connection terminal of the hybrid circuit 8 to a preset value;

[0101] like Figure 6 As shown, it also includes: detecting the amplitude of the opposite end signal received by the hybrid circuit 8;

[0102] Comparing the amplitude of the detected opposite-end signal with a predetermined threshold value and outputting a comparison signal;

[0103] The amplitude of the local end signal sent by the line driver 1 is controlled according to the comparison signal.

[0104] As a preferred embodiment, the present invention further comprises:

[0105] When the amplitude of the peer signal is greater than a predetermined threshold, the amplitude of the local signal sent is reduced by half;

[0106] When the amplitude of the opposite-end signal is less than or equal to a predetermined threshold, the local-end signal is sent according to its original amplitude.

[0107] Specifically, in this embodiment, by limiting the sending amplitude at this end, the swing at the transmission gate is smaller, the operating voltage range is smaller, and the transmission gate operates at an intermediate voltage, ensuring that the power supply voltage of the transmission gate is always within a safe range, thereby achieving overvoltage protection.

[0108] It should be noted that, while the embodiment of the present invention uses a differential line driver as an example, the solution of the present invention is also applicable to a single-ended line driver 1. That is, in a case where there is only one transmission line, an impedance calibration circuit is designed on the transmission line to implement impedance calibration, and amplitude limiting is performed based on the detection amplitude to implement overvoltage protection during impedance calibration. The principles of this circuit are similar to those of the differential line driver 1 and will not be further elaborated here.

[0109] The beneficial effects of adopting the above technical solution are: the present invention limits the impedance between the line driver and the first and second connection terminals of the hybrid circuit to a preset value through a transmission gate, thereby achieving impedance calibration, and its operating voltage range is narrower, and its tolerance for Ethernet reliability is better; and by detecting the transmission amplitude of the other end, the transmission amplitude of the local end is limited according to the transmission amplitude of the other end, thereby achieving overvoltage protection for impedance calibration.

[0110] Through the description and drawings, typical embodiments of the specific structure of the specific implementation are given. Based on the spirit of the present invention, other transformations can be made. Although the above invention has proposed the existing preferred embodiments, however, these contents are not intended to be limiting.

[0111] Various changes and modifications will undoubtedly become apparent to those skilled in the art upon reading the foregoing description. Therefore, the appended claims should be construed to encompass all changes and modifications within the true intent and scope of the present invention. Any and all equivalents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. A line driver impedance calibration overvoltage protection circuit, applied to Ethernet, characterized in that: include: A first impedance calibration circuit is connected between a line driver and a first connection terminal of a hybrid circuit, wherein the first impedance calibration circuit includes: a plurality of first transmission gates, each of the first transmission gates having two ends connected to a first resistor and a second resistor, and each of the first transmission gates being controllably turned on or off by a switch control signal to adjust the impedance between the line driver and the first connection end to a preset value; an overvoltage protection circuit, connected to the line driver and the hybrid circuit, respectively, the overvoltage protection circuit comprising: an amplitude detection circuit, configured to detect the amplitude of a peer signal received by the hybrid circuit; a digital control circuit, configured to compare the amplitude of the opposite-end signal with a predetermined threshold value and output a comparison signal; an amplitude control circuit, configured to control the amplitude of the local-end signal sent by the line driver according to the comparison signal; A first voltage divider circuit, configured to output a first intermediate voltage; A second voltage divider circuit, configured to output a second intermediate voltage; a level conversion unit, wherein the input end of the level conversion unit is respectively connected to the first voltage divider circuit and the second voltage divider circuit, and the output end of the level conversion unit is respectively connected to each of the first transmission gates, and is configured to switch between the first intermediate voltage and the second intermediate voltage to output the switch control signal, thereby controlling the branches between the line driver and the first connection end, where the branches of the first transmission gates are located, to be respectively turned on or off.

2. The line driver impedance calibration overvoltage protection circuit according to claim 1, characterized in that: Also includes: a second impedance calibration circuit connected between the line driver and the second connection terminal of the hybrid circuit, the second impedance calibration circuit comprising: and a plurality of second transmission gates, each of which has two ends connected to a third resistor and a fourth resistor, respectively. Each of the second transmission gates can be controlled to be turned on or off under the action of the switch control signal to adjust the impedance between the line driver and the second connection end to the preset value.

3. A line driver impedance calibration overvoltage protection circuit according to any one of claims 1 or 2, characterized in that: When the amplitude of the opposite-end signal is greater than the predetermined threshold, the amplitude control circuit controls the amplitude of the local-end signal to be sent to be halved; When the amplitude of the opposite-end signal is less than or equal to the predetermined threshold, the local-end signal is sent according to its original amplitude.

4. The line driver impedance calibration overvoltage protection circuit according to claim 1, characterized in that: The first transmission gate includes: A first PMOS transistor and a first NMOS transistor having source and drain electrodes connected in parallel; The gate of the first PMOS transistor is connected to the switch control signal, the drain of the first PMOS transistor is connected to the first resistor, and the source of the first PMOS transistor is connected to the second resistor; The gate of the first NMOS transistor is connected to the inverted signal of the switch control signal.

5. The line driver impedance calibration overvoltage protection circuit according to claim 2, characterized in that: Also includes: A first voltage divider circuit, configured to output a first intermediate voltage; A second voltage divider circuit, configured to output a second intermediate voltage; a level conversion unit, wherein the input end of the level conversion unit is respectively connected to the first voltage divider circuit and the second voltage divider circuit, and the output end of the level conversion unit is respectively connected to each of the second transmission gates, and is used to switch between the first intermediate voltage and the second intermediate voltage to output the switch control signal, thereby controlling the branch between the line driver and the second connection end where each of the second transmission gates is located to be turned on or off.

6. The line driver impedance calibration overvoltage protection circuit according to claim 2, characterized in that: The second transmission gate includes: a second PMOS transistor and a second NMOS transistor with their source and drain connected in parallel; The gate of the second PMOS transistor is connected to the switch control signal, the drain of the second PMOS transistor is connected to the third resistor, and the source of the second PMOS transistor is connected to the fourth resistor; The gate of the second NMOS transistor is connected to the inverted signal of the switch control signal.

7. The line driver impedance calibration overvoltage protection circuit according to claim 1, characterized in that: The line driver is a voltage-type line driver.

8. A line driver impedance calibration overvoltage protection method, characterized in that: Applied to a line driver impedance calibration overvoltage protection circuit according to any one of claims 1 to 7, the method comprising: Under the action of a switch control signal, each of the first transmission gates can be controlled to be turned on or off to adjust the impedance between the line driver and the first connection terminal of the hybrid circuit to a preset value; and / or Under the action of the switch control signal, each second transmission gate can be controlled to be turned on or off to adjust the impedance between the line driver and the second connection terminal of the hybrid circuit to the preset value; The method further includes: detecting the amplitude of the opposite end signal received by the hybrid circuit; comparing the detected amplitude of the opposite-end signal with a predetermined threshold and outputting a comparison signal; The amplitude of the local end signal sent by the line driver is controlled according to the comparison signal.

9. The line driver impedance calibration overvoltage protection method according to claim 8, characterized in that: Also includes: When the amplitude of the opposite-end signal is greater than the predetermined threshold, controlling the amplitude of the local-end signal to be sent to be halved; When the amplitude of the opposite-end signal is less than or equal to the predetermined threshold, the local-end signal is sent according to its original amplitude.

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