Driving circuit and method applied to PAM4

Abstract

The invention relates to the technical field of integrated circuits, and discloses a driving circuit and method applied to a PAM4. The method comprises the following steps: initializing the N-Over-N driver circuit and the impedance calibration circuit; adjusting the number of driving units of the N-Over-N driver circuit connected in parallel with a terminating resistor according to whether the terminating resistor meets an expected standard; adjusting the number of calibration units of the impedance calibration circuit connected in parallel to the terminating resistor according to whether the terminating resistor meets an expected standard; when the swing of the output signal of the N-Over-N driver circuit does not meet the requirement, increasing or decreasing the number of calibration units of the impedance calibration circuit connected in parallel with the terminating resistor; adjusting an output voltage control word of the pre-driver power supply according to whether the terminating resistance meets an expected standard; an output voltage control word of the driver power supply is adjusted according to a swing of an output signal of the N-Over-N driver circuit. According to the invention, high-efficiency and flexible wired data transmission can be realized, nonlinearity of output signals is reduced, and signal transmission quality and reliability are improved.

Description

Technical Field

[0001] The present application relates to the field of integrated circuit technology, and in particular to a driving circuit and method applied to PAM4. Background Art

[0002] In the rapid development of the semiconductor industry, the design complexity and functionality of integrated circuits (ICs) have been significantly enhanced. However, this technological advancement is not without cost. The miniaturization of transistor size and the increase in clock frequency have led to a significant increase in the logic density inside the chip.

[0003] With the development of technologies such as cloud computing, big data, and the Internet of Things, the demand for data transmission rate and bandwidth is growing, and data transmission rate has become one of the key indicators for measuring the performance of electronic systems. In modern electronic systems, high-speed serial communication technology has become the mainstream method of data transmission. Serial communication technology has been widely used in various electronic devices due to its advantages of providing high data transmission rate, reducing the number of pins, and reducing system costs. One of the core components of serial communication technology is the driver, which is responsible for converting digital signals into voltage swing signals suitable for transmission.

[0004] In low-loss wired data transmission applications, industry communication standards do not have high requirements for signal swing, but have different requirements for speed and protocol. In the process of high-speed data transmission, signal integrity is affected by multiple factors such as channel attenuation, crosstalk, and reflection.

[0005] Traditional drivers have deficiencies in power consumption and linearity at low swings. As the demand for high-speed data transmission rates increases, traditional driver designs face severe challenges. Traditional current-mode drivers consume a lot of power when operating at high speeds. This is because they usually require higher currents to drive the loads on the signal lines, and the adjustment of the signal swing is often accompanied by increased power consumption. Current-mode drivers have certain limitations in design, such as sensitivity to process variations and high design complexity.

[0006] In addition to current mode drivers, traditional voltage mode driver designs often use source series terminated drivers. Source series terminated drivers face great challenges in terms of power supply rejection ratio, output common mode noise, and linearity at low voltage. Traditional voltage mode driver designs cannot effectively deal with these effects, resulting in reduced signal quality.

[0007] This section is intended to provide a background or context to the embodiments of the present application as recited in the claims. The description herein is not admitted to be prior art as disclosed by virtue of its inclusion in this section. Summary of the invention

[0008] The purpose of the present application is to provide a driving circuit and method for PAM4. As a new serial deserializer transmitter driving circuit, it can achieve high-linearity signal transmission at a low power supply voltage, and the harmonic components in the output signal are low. It has the characteristics of simple structure, low power consumption and robustness, and can support PAM4 signal modulation, with low requirements for channel insertion loss, and can provide a flexible and high-quality signal transmission solution for chip-to-chip interconnection.

[0009] The present application discloses a driving circuit applied to PAM4, comprising: a PAM4 mapping circuit, a pre-driver power supply, a driver power supply, a pre-driver circuit, an N-Over-N driver circuit, an impedance calibration circuit, and a termination resistor; wherein the pre-driver power supply is coupled to the pre-driver circuit and provides power to the pre-driver circuit, the driver power supply is coupled to the N-Over-N driver circuit and the impedance calibration circuit and provides power to the N-Over-N driver circuit and the impedance calibration circuit, the impedance calibration circuit is coupled to the output end of the N-Over-N driver circuit, and the termination resistor is coupled to the output end of the N-Over-N driver circuit;

[0010] Wherein, the PAM4 mapping circuit is coupled to the pre-driver circuit and converts the input digital signal into a weight code data stream and outputs it to the pre-driver circuit, the pre-driver circuit drives the N-Over-N driver circuit according to the weight code data stream, and the N-Over-N driver circuit and the impedance calibration circuit are used to adjust the termination resistance at the output end of the termination resistor; when the swing of the output signal of the N-Over-N driver circuit does not meet the requirements, the pre-driver power supply is used to dynamically adjust the termination resistance at the output end of the termination resistor, and the driver power supply is used to dynamically adjust the swing of the output signal of the N-Over-N driver circuit.

[0011] In a preferred example, the N-Over-N driver circuit includes a plurality of driving units, each driving unit includes an MSB driving unit and an LSB driving unit;

[0012] Wherein, the MSB driving unit and the LSB driving unit each include: a first transistor, a second transistor, a third transistor and a fourth transistor; the gate of the first transistor and the gate of the fourth transistor are connected to a first node, the drain of the first transistor and the drain of the second transistor are connected, the source of the first transistor and the drain of the third transistor are connected to a second node, the source of the second transistor and the drain of the fourth transistor are connected to a third node, the source of the third transistor and the source of the fourth transistor are connected, and the gate of the second transistor and the gate of the third transistor are connected to a fourth node;

[0013] Among them, the first node and the fourth node of the MSB driving unit respectively receive a pair of differential MSB driving signals from the pre-driver circuit, and the first node and the fourth node of the LSB driving unit respectively receive a pair of differential LSB driving signals from the pre-driver circuit; the third nodes of the MSB driving unit and the LSB driving unit are both connected to the first output terminal, and the second nodes of the MSB driving unit and the LSB driving unit are both connected to the second output terminal.

[0014] In a preferred example, the impedance calibration circuit includes a plurality of calibration units, each calibration unit includes: a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor; the gate of the fifth transistor and the gate of the eighth transistor are connected to a fifth node, the drain of the fifth transistor and the drain of the sixth transistor are connected, the source of the fifth transistor and the drain of the seventh transistor are connected to a sixth node, the source of the sixth transistor and the drain of the eighth transistor are connected to a seventh node, the source of the seventh transistor and the source of the eighth transistor are connected, and the gate of the sixth transistor and the gate of the seventh transistor are connected to an eighth node;

[0015] The fifth node and the eighth node are respectively connected to a pair of differential calibration signals, the seventh node is connected to the first output terminal, and the sixth node is connected to the second output terminal.

[0016] In a preferred example, the terminating resistor is coupled to the first output terminal and the second output terminal of the N-Over-N driver circuit respectively.

[0017] In a preferred example, it also includes: a resistance detection module, the input of which is coupled to the pre-driver power supply and the driver power supply respectively, and the output of which is coupled to the output end of the termination resistor and is used to indicate whether the current resistance value meets the expected standard.

[0018] In a preferred example, the resistance detection module is implemented in any of the following ways: an analog-to-digital converter, an analog comparator.

[0019] In a preferred example, it also includes: a swing detection module, the input of which is coupled to the pre-driver power supply and the driver power supply respectively, and the output of which is coupled to the output end of the termination resistor and is used to indicate whether the current swing value meets the expected standard.

[0020] In a preferred example, the swing detection module is implemented in any of the following ways: an analog-to-digital converter, an analog comparator.

[0021] The present application discloses a driving method applied to PAM4, using the above-mentioned driving circuit, the method comprising:

[0022] Initializing the N-Over-N driver circuit and the impedance calibration circuit;

[0023] adjusting the number of driving units of the N-Over-N driver circuit connected in parallel to the termination resistor according to whether the termination resistor meets the expected standard;

[0024] adjusting the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor according to whether the termination resistor meets the expected standard;

[0025] When the swing of the output signal of the N-Over-N driver circuit does not meet the requirement, increasing or decreasing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor;

[0026] adjusting the output voltage control word of the pre-driver power supply according to whether the termination resistance meets the expected standard; and

[0027] The output voltage control word of the driver power supply is adjusted according to the swing of the output signal of the N-Over-N driver circuit.

[0028] In a preferred example, when the swing of the output signal of the N-Over-N driver circuit does not meet the requirement, increasing or decreasing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor further comprises:

[0029] When the swing amplitude of the output signal of the N-Over-N driver circuit is too small, reducing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor;

[0030] When the swing amplitude of the output signal of the N-Over-N driver circuit is too large, the number of calibration units of the impedance calibration circuit connected in parallel with the terminating resistor is increased.

[0031] The present invention proposes a driving circuit for PAM4 signals, including a driver power supply, a pre-driver power supply, a pre-driver, an N-Over-N driver circuit and a resistance calibration circuit. The power supply module is a voltage regulator with adjustable output voltage and is used to achieve output swing adjustment. The pre-driver is used to drive the subsequent N-Over-N driver. The resistance calibration circuit is connected to the output end of the N-Over-N driver to adjust the slew rate of the output signal. The driving circuit simultaneously realizes channel equalization, resistance calibration, slew rate adjustment and differential output amplitude adjustment functions through the driver power supply, pre-driver power supply, pre-driver, N-Over-N driver and resistance calibration circuit.

[0032] The driving circuit of the present invention can realize efficient and flexible wired data transmission, reduce the nonlinearity of the output signal, and improve the signal transmission quality and reliability.

[0033] The specification of the present application records a large number of technical features, which are distributed in various technical solutions. If all possible combinations of technical features of the present application (i.e., technical solutions) are to be listed, the specification will be too long. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of the present application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions should all be regarded as having been recorded in this specification), unless the combination of such technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed, and features C and D are equivalent technical means that play the same role. Technically, only one can be used, and it is impossible to use them at the same time. Feature E can be combined with feature C technically. Then, the solution of A+B+C+D should not be regarded as having been recorded because it is technically infeasible, and the solution of A+B+C+E should be regarded as having been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a circuit diagram of a driving circuit applied to PAM4 according to an embodiment of the present application.

[0035] Figure 2 is a circuit diagram of a driving unit of an N-Over-N driver circuit according to an embodiment of the present application.

[0036] Figure 3 4 is a circuit diagram of a calibration unit of an impedance calibration circuit according to an embodiment of the present application.

[0037] Figure 4 It is a flowchart of a driving method applied to PAM4 according to one embodiment of the present application.

[0038] Figure 5 It is a more detailed flow chart of a driving method applied to PAM4 according to one embodiment of the present application. DETAILED DESCRIPTION

[0039] In the following description, many technical details are provided to help readers better understand the present application. However, those skilled in the art can understand that the technical solution claimed in the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0040] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0041] The first embodiment of the present application relates to a driving circuit applied to PAM4, and its structure is as follows Figure 1 As shown, the driving circuit 100 includes: a PAM4 mapping circuit 107, a pre-driver power supply 101, a driver power supply 102, a pre-driver circuit 104, an N-Over-N driver circuit 105, an impedance calibration circuit 103, and a termination resistor 108. The pre-driver power supply 101 is coupled to the pre-driver circuit 104 and provides power to the pre-driver circuit 104. The driver power supply 102 is coupled to the N-Over-N driver circuit 105 and the impedance calibration circuit 103 and provides power to the N-Over-N driver circuit 105 and the impedance calibration circuit 103. It should be noted that the driving circuit may further include a total power supply 109, which is respectively coupled to the pre-driver power supply 101 and the driver power supply 102, and supplies power to the pre-driver power supply 101 and the driver power supply 102.

[0042] The PAM4 mapping circuit 107 is coupled to the pre-driver circuit 104 and converts the input digital signal into a weight code data stream and outputs it to the pre-driver circuit 104. The pre-driver power supply 101 is used to dynamically adjust the voltage state of the output signal of the N-Over-N driver circuit 105 to adapt to the slew rate requirements of different application scenarios. The driver power supply 102 is used to dynamically adjust the voltage state of the output signal of the N-Over-N driver circuit 105 to offset the termination resistance mismatch. The pre-driver circuit 104 drives the N-Over-N driver circuit 105 according to the weight code data stream. The impedance calibration circuit 103 is coupled to the output end of the N-Over-N driver circuit 105 and is used to adjust the slew rate of the output signal of the N-Over-N driver circuit 105. The termination resistor 108 is coupled to the output end of the N-Over-N driver circuit 105.

[0043] The N-Over-N driver circuit 105 is used to adjust the termination resistance at the output end of the termination resistor 108 to roughly match the termination resistance. The impedance calibration circuit 103 is used to adjust the termination resistance at the output end of the termination resistor 108 to further roughly match the termination resistance. When the swing of the output signal of the N-Over-N driver circuit 105 does not meet the requirements, the pre-driver power supply 101 is used to dynamically adjust the termination resistance at the output end of the termination resistor 108, and the driver power supply 102 is used to dynamically adjust the output swing of the output signal of the N-Over-N driver circuit 105.

[0044] In one embodiment, the N-Over-N driver circuit includes a plurality of driving units, each of which includes an MSB driving unit and an LSB driving unit (the MSB driving unit and the LSB driving unit are collectively referred to as an N-Over-N driving unit). Figure 2 1 is a circuit diagram of a driving unit 200 in an embodiment, wherein the driving unit 200 includes an LSB driving unit 201 and an MSB driving unit 202, wherein the LSB driving unit 201 is used to implement a pull-down function, and the MSB driving unit 202 is used to implement a pull-up function. The LSB driving unit 201 and the MSB driving unit 202 each include: a first transistor M1, a second transistor M2, a third transistor M3, and a fourth transistor M4. The gate of the first transistor M1 and the gate of the fourth transistor M4 are connected to a first node S1, the drain of the first transistor M1 and the drain of the second transistor N2 are connected, the source of the first transistor M1 and the drain of the third transistor M3 are connected to a second node S2, the source of the second transistor M2 and the drain of the fourth transistor M4 are connected to a third node S3, the source of the third transistor M3 and the source of the fourth transistor M4 are connected, and the gate of the second transistor M2 and the gate of the third transistor M3 are connected to a fourth node S4.

[0045] The first node S1 and the fourth node S4 of the MSB driving unit 202 respectively receive a pair of differential MSB driving signals Vip_msb and Vin_msb from the pre-driver circuit 104, and the first node S1 and the fourth node S4 of the LSB driving unit 201 respectively receive a pair of differential LSB driving signals Vip_lsb and Vin_lsb from the pre-driver circuit 104. The third node S3 of the MSB driving unit 202 and the LSB driving unit 201 are both connected to the first output terminal vop, and the second node S2 of the MSB driving unit 202 and the LSB driving unit 201 are both connected to the second output terminal von.

[0046] In one embodiment, the impedance calibration circuit 103 includes a plurality of calibration units. Figure 3 is a circuit diagram of a calibration unit 300 in an embodiment, wherein the calibration unit 300 includes a fifth transistor M5, a sixth transistor M6, a seventh transistor M7, and an eighth transistor M8. The gate of the fifth transistor M5 and the gate of the eighth transistor M8 are connected to a fifth node S5, the drain of the fifth transistor M5 and the drain of the sixth transistor M6 are connected, the source of the fifth transistor M5 and the drain of the seventh transistor M7 are connected to a sixth node S6, the source of the sixth transistor M6 and the drain of the eighth transistor M8 are connected to a seventh node S7, the source of the seventh transistor M7 and the source of the eighth transistor M8 are connected, and the gate of the sixth transistor M6 and the gate of the seventh transistor M7 are connected to an eighth node S8.

[0047] It should be noted that the structure of the calibration unit is the same as that of the N-Over-N driving unit, the difference being that the driving unit 200 receives the driving signal from the pre-driver circuit 104, while the calibration unit receives static 0, 1 signals. Specifically, the fifth node S5 and the eighth node S8 receive a pair of differential calibration signals CAL_P and CAL_N, respectively, the seventh node S7 is connected to the first output terminal vop, and the sixth node S6 is connected to the second output terminal von.

[0048] In one embodiment, the termination resistor 108 is coupled to the first output terminal vop and the second output terminal von of the N-Over-N driver circuit 105 , respectively.

[0049] In one embodiment, the driving circuit applied to PAM4 further includes: a resistance detection module 106, the input of the resistance detection module 106 is respectively coupled to the pre-driver power supply 101 and the driver power supply 102, and the output of the resistance detection module 106 is coupled to the output end of the termination resistor 108 and is used to indicate whether the current resistance value meets the expected standard. For example, the resistance detection module 106 compares the current resistance value of the output end of the termination resistor 108 with the expected standard value, and determines whether the current resistance value is larger or smaller than the expected standard value according to the size of the current resistance value and the expected standard value, thereby performing impedance adjustment.

[0050] In one embodiment, the resistance detection module 106 is implemented in any of the following ways: an analog-to-digital converter, an analog comparator.

[0051] In one embodiment, the driving circuit applied to PAM4 further includes: a swing detection module 110, the input of the swing detection module 110 is coupled to the pre-driver power supply 101 and the driver power supply 110 respectively, and the output of the swing detection module 110 is coupled to the output end of the termination resistor 108 and is used to indicate whether the current swing value meets the expected standard. For example, the swing detection module 110 compares the output voltage swing of the N-Over-N driver with the expected standard value, and determines whether the current voltage swing is larger or smaller than the expected standard value according to the size of the current voltage swing and the expected standard value, thereby adjusting the output voltage swing.

[0052] In one embodiment, the swing detection module 106 is implemented by any of the following methods: an analog-to-digital converter, an envelope detection circuit, or an analog comparator.

[0053] The second embodiment of the present application relates to a driving method applied to PAM4, the process of which is as follows: Figure 4 As shown, the method comprises the following steps:

[0054] Step 401 , initializing an N-Over-N driver circuit and an impedance calibration circuit.

[0055] Step 402, adjust the number of driving units of the N-Over-N driver circuit connected in parallel to the termination resistor according to whether the termination resistance meets the expected standard. For example, if the current differential termination resistance of the entire circuit is 130 ohms, the resistance detection module 106 will indicate that the current differential termination resistance is larger than the standard termination resistance of 100 ohms, then consider increasing the number of driving units of the N-Over-N driver circuit connected in parallel to the termination resistor. Assuming that the current number of parallel connections is 33, try to connect 34 in parallel, and detect again. If it is still too large, increase the number again, and so on; if the resistance is too small, stop increasing the number of parallel connections. When the total number of driving units in the N-Over-N driver circuit is too small, and all of them cannot meet the output termination resistance requirements even if they are connected to the output end, all the driving units of the N-Over-N driver circuit are connected to the output end, and the resistance is calibrated using subsequent steps. In the above example, calibrating 130 ohms composed of 33 units to 100 ohms requires an additional 10 units. However, due to power consumption considerations, the number of N-Over-N drive units in the system is generally less than or equal to 40, so only 7 additional units are connected in parallel, and the residual resistance error is calibrated using subsequent steps. When the termination resistance is small, according to similar ideas as above, the N-Over-N driver circuit units connected in parallel to the output end are reduced in sequence until the resistance detection module indicates that the current termination resistance is greater than the standard termination resistance of 100 ohms, and the residual resistance error is calibrated using subsequent steps. In one embodiment, whether the termination resistance meets the expected standard is completed by the above-mentioned resistance detection module 106.

[0056] Step 403, according to whether the termination resistance meets the expected standard, the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor is adjusted. If the resistance detection module 106 indicates that the current differential termination resistance is larger than the standard termination resistance of 100 ohms, consider increasing the number of calibration units of the impedance calibration circuit. Assuming that the current number of parallel connections is 0, try to connect 1 in parallel, and detect again. If it is still too large, increase the number again, and so on; if the resistance is too small, stop increasing the number of parallel connections. When the total number of calibration units of the impedance calibration circuit is too small, and all of them cannot meet the output termination resistance requirements when connected to the output end, the calibration units of all impedance calibration circuits are connected to the output end, and the resistance is calibrated using subsequent steps. In the above example 402, a 130 ohm driver consisting of 33 N-Over-N drive units is connected in parallel with an additional 7 N-Over-N drive units. After step 402 is completed, the termination resistance is calibrated to 107 ohms. The termination resistance is further reduced by sequentially increasing the number of calibration units of the impedance calibration circuit until the resistance detection module 106 indicates that the current differential termination resistance is smaller than the marked resistance of 100 ohms, and then the number of connected impedance calibration units is stopped from being increased.

[0057] Step 404, when the swing of the output signal of the N-Over-N driver circuit does not meet the requirements, increase or decrease the number of calibration units of an impedance calibration circuit connected in parallel to a termination resistor. After completing steps 402 and 403 in sequence, the output termination resistance is relatively matched, but the calibration unit of step 403 will reduce the output swing of the driver circuit, limiting the application of the driver circuit in certain application scenarios. Therefore, if the swing of the output signal of the N-Over-N driver circuit does not meet the requirements, it can be considered to increase or decrease a calibration unit in sequence, and further adjust the termination resistance and output swing through the pre-driver power supply and the driver power supply. When the swing of the output signal of the N-Over-N driver circuit is too small, reduce the number of calibration units of an impedance calibration circuit connected in parallel to a termination resistor. When the swing of the output signal of the N-Over-N driver circuit is too large, increase the number of calibration units of an impedance calibration circuit connected in parallel to a termination resistor. In one embodiment, whether the swing meets the expected standard is completed by the above-mentioned swing detection module 110.

[0058] Step 405, adjust the output voltage control word of the pre-driver power supply according to whether the termination resistance meets the expected standard. For example, in the example of 403, by connecting three impedance calibration units in parallel, the resistance can be calibrated to 99.7 ohms, which is very close to the standard resistance of 100 ohms, but a certain output swing is lost. In this step, first try to turn off one impedance calibration unit. At this time, the resistance detection unit will indicate that the output termination resistance is too large. By gradually increasing the output voltage control word of the pre-driver power supply and increasing the driver power supply voltage, the output termination resistance can be reduced until the resistance detection module indicates that the current termination resistance is less than the standard termination resistance. This method improves the output swing while maintaining the matching of the output termination resistance. When the output swing is too large and it is desired to reduce the output swing, the signal quality can be improved by increasing the number of calibration units and reducing the pre-driver power supply voltage.

[0059] Step 406, adjust the output voltage control word of the driver power supply according to the swing of the output signal of the N-Over-N driver circuit. Similar to step 405, when the output swing is too small, the signal quality can be improved by increasing the power control word and reducing the number of calibration units connected in parallel; when the output swing is too large, adjust in the opposite direction.

[0060] In order to better understand the technical solution of the present application, a specific example is provided below for illustration. The details listed in the example are mainly for ease of understanding and are not intended to limit the scope of protection of the present application.

[0061] like Figure 1As shown, the input digital signal is converted into the weight code data stream required by the pre-driver 104 through the PAM4 mapping circuit 107, and the pre-driver 104 drives the N-Over-N driver 105 after buffering the signal. The power supplies of the pre-driver 104 and the N-Over-N driver 105 are respectively provided by the pre-driver power supply 101 and the driver power supply 102. The series value of the output resistance of the N-Over-N driver 105 and the series termination resistor 108 needs to match the characteristic impedance of the transmission line, so as to minimize the reflection of the output signal.

[0062] The implementation methods of the pre-driver power supply 101 and the driver power supply 102 include but are not limited to linear regulated power supplies and switching power supplies. The output voltages of the pre-driver power supply 101 and the driver power supply 102 should support digital adjustment functions. The range of the digitally adjusted output voltage is not less than 10%. The N-Over-N driver 105 and the impedance calibration circuit 103 are obtained by connecting a number of N-Over-N drive units in parallel. Under the adaptive adjustment of the pre-driver power supply 101 and the driver power supply 102, the power supply voltage of the pre-driver circuit 104 and the power supply voltage of the N-Over-N driver 105 are adjusted to appropriate values, so that the output resistance and output signal swing of the entire drive circuit reach the optimal value. The implementation methods of the resistance detection module 106 include but are not limited to detection circuits such as digital-to-analog converters and analog comparators. The output signal of the resistance detection module 106 should be a multi-bit or single-bit digital signal to indicate whether the current resistance meets the expected standard.

[0063] Figure 2 FIG. 2 shows a schematic diagram of the structure of the N-Over-N drive unit of the present invention. Figure 2 As shown, the N-Over-N driving unit 200 is a dual NMOS series stacked structure, and a single N-Over-N driving unit is composed of 4 N-type metal oxide field effect transistors. In the present invention, the N-over-N driving unit 200 supports both the non-return to zero (NRZ) signal and the 4th-order pulse amplitude modulation (PAM) signal. To support the PAM4 signal, the N-over-N driving unit 200 is divided into a minimum weight slice LSB slice 201 and a maximum weight slice MSB slice 202. By properly configuring the input data of the LSB slice 201 and the MSB slice 202, the conversion of the input digital signal to the analog signal can be completed.

[0064] The N-Over-N driver is a fully differential driver, with a fully differential digital signal as input and a fully differential analog signal as output. Taking the MSB slice as an example, the drains of the pull-up transistors M1 and M2 are connected to the power supply, the gates are connected to the input digital signals Vip_msb and Vin_msb respectively, and the sources are connected to the output terminals Von and Vop respectively. The drains of the pull-down transistors M3 and M4 are connected to the power supply, the gates are connected to the input digital signals Vin_msb and Vip_msb respectively, and the sources are connected to the output terminals Von and Vop respectively. Depending on the application scenario, the output of the N-Over-N driver can adopt a variety of connection methods such as DC coupling or AC coupling.

[0065] Figure 5 FIG. 2 shows a flow chart of resistance calibration and slew rate adjustment according to an embodiment. Figure 5 As shown, according to the different precision characteristics of different resistance adjustment means, the present invention achieves the best resistance calibration effect through a complete calibration process. In the initial stage of resistance calibration, the impedance calibration circuit 103 and the N-Over-N driver 105 should be initialized, and the termination resistance is roughly matched by various means such as the on-chip resistance detection module 106 or the off-chip oscilloscope; if the termination resistance does not meet the rough matching requirements, the number k of parallel connected resistors in the impedance calibration circuit 103 and the N-Over-N driver 105 should be reselected, and the resistance detection should be performed again; if the rough matching is completed, the pre-driver power supply output voltage adjustment cycle is entered.

[0066] In the pre-driver power supply output voltage adjustment cycle stage, the output voltage control words of the pre-driver power supply 101 and the driver power supply 102 should be initialized first. If the output termination resistance does not meet the matching requirements, the output voltage control word of the pre-driver power supply 101 is reselected, and the output voltage control word of the driver power supply 102 is kept unchanged; if the termination resistance meets the matching requirements, the next stage is entered. According to the adjustment in the previous stage, the on-chip resistance detection module 106 is used to determine whether the output swing and other indicators meet the application requirements. If they do not meet the requirements, the output voltage control word of the driver power supply 102 is reselected, and the resistance is determined based on the output digital signal of the resistance detection module 106. Matching until the resistance reaches the best matching condition.

[0067] The present invention realizes multiple functions such as output signal slew rate adjustment and output terminal resistance correction by jointly tuning the output voltage of the pre-driver power supply and the driver power supply. The higher the output voltage of the pre-driver power supply, the smaller the output terminal resistance, and the greater the output signal slew rate; the smaller the output voltage of the driver power supply, the smaller the output terminal resistance, and the smaller the output signal slew rate.

[0068] The basic unit of the N-Over-N driver circuit and the resistance calibration circuit is the N-Over-N driver unit. By selecting the number of N-Over-N driver units connected to the output port, the output termination resistance can be adjusted. The N-Over-N driver unit has both a pull-up unit and a pull-down unit to maintain the common mode voltage of the output driver unchanged. The calibration circuit realizes the function of output termination resistance calibration without affecting the output signal quality of the driver circuit.

[0069] It should be noted that in the application documents of this patent, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements. In the application documents of this patent, if it is mentioned that an action is performed according to an element, it means that the action is performed at least according to the element, which includes two situations: performing the action only according to the element, and performing the action according to the element and other elements. Expressions such as multiple, multiple, and multiple include 2, 2 times, 2 kinds, and more than 2, more than 2 times, and more than 2 kinds.

[0070] All documents mentioned in this specification are considered to be included in the disclosure of this application as a whole, so that they can be used as a basis for modification when necessary. In addition, it should be understood that the above is only a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this specification should be included in the scope of protection of one or more embodiments of this specification.

[0071] In some cases, the actions or steps described in the claims may be performed in a different order than in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A driving circuit applied to PAM4, characterized in that: include: A PAM4 mapping circuit, a pre-driver power supply, a driver power supply, a pre-driver circuit, an N-Over-N driver circuit, an impedance calibration circuit, and a termination resistor; wherein the pre-driver power supply is coupled to the pre-driver circuit and provides power to the pre-driver circuit, the driver power supply is coupled to the N-Over-N driver circuit and the impedance calibration circuit and provides power to the N-Over-N driver circuit and the impedance calibration circuit, the impedance calibration circuit is coupled to an output terminal of the N-Over-N driver circuit, and the termination resistor is coupled to an output terminal of the N-Over-N driver circuit; Wherein, the PAM4 mapping circuit is coupled to the pre-driver circuit and converts the input digital signal into a weight code data stream and outputs it to the pre-driver circuit, the pre-driver circuit drives the N-Over-N driver circuit according to the weight code data stream, and the N-Over-N driver circuit and the impedance calibration circuit are used to adjust the termination resistance at the output end of the termination resistor; when the swing of the output signal of the N-Over-N driver circuit does not meet the requirements, the pre-driver power supply is used to dynamically adjust the termination resistance at the output end of the termination resistor, and the driver power supply is used to dynamically adjust the swing of the output signal of the N-Over-N driver circuit.

2. The driving circuit according to claim 1, characterized in that: The N-Over-N driver circuit includes a plurality of driving units, each driving unit including an MSB driving unit and an LSB driving unit; Wherein, the MSB driving unit and the LSB driving unit each include: a first transistor, a second transistor, a third transistor and a fourth transistor; the gate of the first transistor and the gate of the fourth transistor are connected to a first node, the drain of the first transistor and the drain of the second transistor are connected, the source of the first transistor and the drain of the third transistor are connected to a second node, the source of the second transistor and the drain of the fourth transistor are connected to a third node, the source of the third transistor and the source of the fourth transistor are connected, and the gate of the second transistor and the gate of the third transistor are connected to a fourth node; Among them, the first node and the fourth node of the MSB driving unit respectively receive a pair of differential MSB driving signals from the pre-driver circuit, and the first node and the fourth node of the LSB driving unit respectively receive a pair of differential LSB driving signals from the pre-driver circuit; the third nodes of the MSB driving unit and the LSB driving unit are both connected to the first output terminal, and the second nodes of the MSB driving unit and the LSB driving unit are both connected to the second output terminal.

3. The driving circuit according to claim 2, characterized in that: The impedance calibration circuit includes a plurality of calibration units, each of which includes: a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor; the gate of the fifth transistor and the gate of the eighth transistor are connected to a fifth node, the drain of the fifth transistor and the drain of the sixth transistor are connected, the source of the fifth transistor and the drain of the seventh transistor are connected to a sixth node, the source of the sixth transistor and the drain of the eighth transistor are connected to a seventh node, the source of the seventh transistor and the source of the eighth transistor are connected, and the gate of the sixth transistor and the gate of the seventh transistor are connected to an eighth node; The fifth node and the eighth node are respectively connected to a pair of differential calibration signals, the seventh node is connected to the first output terminal, and the sixth node is connected to the second output terminal.

4. The driving circuit according to claim 2, characterized in that: The terminating resistors are coupled to the first output terminal and the second output terminal of the N-Over-N driver circuit, respectively.

5. The driving circuit according to claim 4, characterized in that: Also includes: A resistance detection module, wherein the input of the resistance detection module is coupled to the pre-driver power supply and the driver power supply respectively, and the output of the resistance detection module is coupled to the output end of the termination resistor and is used to indicate whether the current resistance value meets the expected standard.

6. The driving circuit according to claim 5, characterized in that: The resistance detection module is implemented by any of the following methods: analog-to-digital converter, analog comparator.

7. The driving circuit according to claim 4, characterized in that: Also includes: A swing detection module, the input of which is coupled to the pre-driver power supply and the driver power supply respectively, and the output of which is coupled to the output end of the terminating resistor and is used to indicate whether the current swing value meets the expected standard.

8. The driving circuit according to claim 7, characterized in that: The swing detection module is implemented by any of the following methods: analog-to-digital converter, analog comparator.

9. A driving method applied to PAM4, characterized in that: Using the driving circuit according to any one of claims 1 to 7, the method comprises: Initializing the N-Over-N driver circuit and the impedance calibration circuit; adjusting the number of driving units of the N-Over-N driver circuit connected in parallel to the termination resistor according to whether the termination resistor meets the expected standard; adjusting the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor according to whether the termination resistor meets the expected standard; When the swing of the output signal of the N-Over-N driver circuit does not meet the requirement, increasing or decreasing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor; adjusting the output voltage control word of the pre-driver power supply according to whether the termination resistance meets the expected standard; and The output voltage control word of the driver power supply is adjusted according to the swing of the output signal of the N-Over-N driver circuit.

10. The driving method according to claim 9, characterized in that: When the swing of the output signal of the N-Over-N driver circuit does not meet the requirement, increasing or decreasing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor further comprises: When the swing amplitude of the output signal of the N-Over-N driver circuit is too small, reducing the number of calibration units of the impedance calibration circuit connected in parallel to the termination resistor; When the swing amplitude of the output signal of the N-Over-N driver circuit is too large, the number of calibration units of the impedance calibration circuit connected in parallel with the terminating resistor is increased.

Images