Predistortion Calibration Method and Apparatus for Digital-to-Analog Converter and Transmitter Using the Apparatus

Abstract

According to an embodiment of the present disclosure, there are provided a predistortion calibration method and apparatus for a digital-to-analog converter and a transmitter using the apparatus. The predistortion calibration apparatus for a digital-to-analog converter includes an error calculation module that calculates, for each thermometer code greater than 0 used by the most significant bit module, the cumulative error of the current source of the most significant bit module corresponding thereto according to the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module; a calibration module that adds a predetermined offset to the least significant bit part of the data to be input to the digital-to-analog converter and calculates the calibrated least significant bit part according to the cumulative error corresponding to the thermometer code of the most significant bit part of the data to be input. The embodiments of the present disclosure perform predistortion in the digital domain and correct the nonlinear error of the digital-to-analog converter by changing the binary code of the LSB part.

Description

Technical Field

[0001] The present disclosure relates to high-speed communication, and in particular to a pre-distortion calibration method and device for a digital-to-analog converter and a transmitter using the device. Background Art

[0002] With the rapid development of chip technology, the performance requirements for digital-analog interface circuits are constantly increasing. For example, high-speed SERDES (serializer / deserializer) technology has developed to single-channel 112GHz / 224GHz nodes. In high-speed interface circuits, the digital-to-analog converter (DAC) is one of the key modules, and its performance directly affects the signal quality and transmission accuracy of the system.

[0003] Current steering DAC has been widely used in the field of high-speed communication and data conversion due to its high speed and high precision. The basic working principle of current steering DAC is to control the on and off of the switch through a digital control signal to determine whether the current of different current sources flows through the load, thereby generating a corresponding output voltage. However, in the actual chip manufacturing process, due to process deviations, the output current of the current source often has errors, resulting in nonlinear problems of the DAC. Therefore, in the existing current steering DAC design, the thermometer code control method is usually used to encode the high bits of the DAC. However, this method can only effectively reduce the differential non-linearity (DNL) error, and cannot significantly improve the integral non-linearity (INL) error.

[0004] In the transmitter circuit of the communication system (such as the transmitter circuit of WiFi and high-speed SERDES), the integral nonlinearity error has a significant impact on the system performance, causing signal distortion, reducing the accuracy of data transmission, and thus affecting the overall performance of the system. Therefore, how to effectively reduce the integral nonlinearity error of the DAC and improve the accuracy of digital-to-analog conversion is an important issue that needs to be solved by those skilled in the art. Summary of the invention

[0005] In view of the problems existing in the prior art, embodiments of the present disclosure provide a method and device for pre-distortion calibration of a digital-to-analog converter.

[0006] The first aspect of the embodiments of the present disclosure provides a pre-distortion calibration device for a digital-to-analog converter, which includes an error calculation module that calculates the cumulative error of the current source of the most significant bit module corresponding to each thermometer code used by the most significant bit module according to the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module; a calibration module that adds a predetermined offset to the least significant bit part of the data to be input to the digital-to-analog converter and calculates the calibrated least significant bit part according to the cumulative error corresponding to the thermometer code of the most significant bit part of the data to be input, wherein the most significant bit module of the digital-to-analog converter is controlled using thermometer codes and the least significant bit module is controlled using binary codes. The calibrated least significant bit part replaces the least significant bit part of the data to be input and is used to control the least significant bit module of the digital-to-analog converter.

[0007] The pre-distortion calibration device of the embodiments of the present disclosure calculates the cumulative error of the current source of the most significant bit module corresponding to the thermometer code, and accordingly changes the binary codeword of the least significant bit to pre-compensate for the error of the current source of the most significant bit module. This method makes it easier to implement the analog circuit part, and the signal-to-noise distortion ratio after correction is significantly improved.

[0008] Optionally, for the pre-distortion calibration device according to the first aspect of the present disclosure, the error calculation module calculates, for each thermometer code, the number of current portions of the output of the most significant bit module relative to the unit current according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module, and the difference between it and the ideal number of current portions corresponding to the thermometer code is used as the cumulative error.

[0009] Optionally, the error calculation module can calculate the cumulative error of the current source corresponding to each thermometer code greater than 0 of the most significant bit module of the digital-to-analog converter through the following equation:

[0010]

[0011] where N is the number of bits of the thermometer code corresponding to the most significant bit module, M + 1 is the number of bits of the binary code corresponding to the least significant bit module, i = 0, 1, … N - 1, Gi represents the cumulative error of the current source of the most significant bit module, and Pj is the ratio between the output of the jth current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module.

[0012] Optionally, for the pre-distortion calibration device according to the first aspect of the present disclosure, the calculation of the least significant bit part of the calibration includes subtracting the thermometer code corresponding to the rounded cumulative error from the least significant bit part of the data to be input with a predetermined offset added when the thermometer code of the most significant bit part of the data to be input is greater than 0. The data to be input refers to the data to be input into the digital-to-analog converter. After the least significant bit part thereof is adjusted according to the pre-determined cumulative error, it is used as the least significant bit part of the calibration to replace the least significant bit part in the original input data, and the output of the current source of the least significant bit module is controlled, thereby compensating for the current source error in the most significant bit module. In the digital-to-analog converter, the most significant bit part of the data to be input is converted from a binary code to a thermometer code for controlling the most significant bit module.

[0013] Optionally, for the pre-distortion calibration device according to the first aspect of the present disclosure, the digital-to-analog converter includes a measurement module for measuring the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module. The measurement module includes a first current-voltage conversion circuit, a second current-voltage conversion circuit, and an analog-to-digital converter. The first current-voltage conversion circuit receives the outputs of all current sources in the least significant bit module, and the output voltage thereof serves as the reference voltage of the analog-to-digital converter. The second current-voltage conversion circuit is connected to one current source in the most significant bit module, and the output voltage thereof serves as the input voltage of the analog-to-digital converter. The analog-to-digital converter outputs the ratio of the input voltage to the reference voltage. This measurement module can quickly and accurately obtain the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module.

[0014] Optionally, the digital-to-analog converter includes the redundant branch, which includes a current source having the same current magnitude as the current source corresponding to the highest bit of the least significant bit part other than the redundant branch. The redundant branch can improve the linearity and dynamic performance of the digital-to-analog converter and improve the accuracy of calibration.

[0015] The second aspect of the embodiments of the present disclosure provides a pre-distortion calibration method for a digital-to-analog converter, including measuring the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module, where the most significant bit module is controlled using a thermometer code, the least significant bit module is controlled using a binary code, and the least significant bit module includes a redundant branch; calculating the cumulative error of the current source of the most significant bit module corresponding to each thermometer code greater than 0 according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module; adding a predetermined offset to the least significant bit part of the data to be input to the digital-to-analog converter, and calculating the calibrated least significant bit part according to the cumulative error corresponding to the thermometer code of the most significant bit part of the data to be input.

[0016] Optionally, according to the second aspect of the embodiments of the present disclosure, measuring the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module includes converting the outputs of all current sources in the least significant bit module through a first current-voltage conversion circuit and then inputting them into an analog-to-digital converter as its reference voltage, converting the output of one current source in the most significant bit module through a second current-voltage conversion circuit and then inputting it into the analog-to-digital converter as its input voltage, and the analog-to-digital converter outputs the ratio of the input voltage to the reference voltage.

[0017] Optionally, according to the second aspect of the embodiments of the present disclosure, calculating the number of current portions of the output of the most significant bit module relative to the unit current for each thermometer code according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module, and the difference between it and the ideal number of current portions corresponding to the thermometer code is used as the cumulative error.

[0018] Optionally, according to the second aspect of the embodiments of the present disclosure, calculating the calibrated least significant bit part includes subtracting the cumulative error corresponding to the thermometer code from the least significant bit part of the data to be input with the predetermined offset added when the thermometer code of the most significant bit part of the data to be input is greater than 0. Optionally, the redundant branch includes a current source, and the current magnitude thereof is the same as that of the current source corresponding to the highest bit of the least significant bit part except for the redundant branch.

[0019] Optionally, a third aspect of the present disclosure provides a serializer / deserializer transmitter, which includes a feed-forward equalizer, a pre-distortion calibration device as described above, a multiplexer, and a digital-to-analog converter connected in sequence. The serializer / deserializer transmitter further includes a clock generation circuit, which provides corresponding clock signals for the feed-forward equalizer, the pre-distortion calibration device, the multiplexer, and the digital-to-analog converter. The digital-to-analog converter includes a measurement module, which measures the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module.

[0020] Implementing any device of the present disclosure does not necessarily require achieving all the above-mentioned advantages simultaneously. Other features and advantages of the present disclosure will be described in the subsequent embodiments of the specification, and part of them will become obvious from the embodiments of the specification, or be understood by implementing the present disclosure. The objectives and advantages of the embodiments of the present disclosure can be realized and obtained by the structures pointed out in the specification, the claims, and the drawings. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present disclosure, rather than a limitation on the present disclosure.

[0022] Figure 1 is a schematic structural diagram of a current-steering digital-to-analog converter in the prior art;

[0023] Figure 2 is a schematic structural diagram of a current-steering digital-to-analog converter according to an embodiment of the present disclosure;

[0024] Figure 3 is for measuring according to an embodiment of the present disclosure Figure 2 a schematic circuit diagram of the output of the current source of the first bit t0 in the MSB part of the digital-to-analog converter shown;

[0025] Figure 4 is for measuring according to an embodiment of the present disclosure Figure 2 a schematic circuit diagram of the output of the current source of the second bit t1 in the MSB part of the digital-to-analog converter shown;

[0026] Figure 5 is a flowchart for calculating the cumulative error of the current source corresponding to each bit in the MSB part;

[0027] Figure 6 is a flowchart of a method for pre-distortion calibration of a digital-to-analog converter based on the cumulative error of the current source;

[0028] Figure 7It is a schematic structural diagram of a SerDes transmitter using the predistortion calibration device of the embodiments of the present disclosure;

[0029] Figure 8 It is a simulation waveform diagram of the signal-to-noise distortion ratio before and after calibration. Specific embodiments

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some but not all of the embodiments of the present disclosure. Various different embodiments can be combined with each other to form other embodiments not shown in the following description. Based on the described embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present disclosure.

[0031] Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present disclosure pertains. The "first", "second" and similar terms used in the specification and claims of the present disclosure do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, the terms such as "a" or "an" do not necessarily denote a quantity limitation. The terms such as "comprising" or "including" mean that the elements or items appearing before the term cover the elements or items listed after the term and their equivalents, without excluding other elements or items. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0032] Figure 1 It shows a schematic structural diagram of a 7-bit current-steering digital-to-analog converter of the prior art. In Figure 1In it, the current-steering digital-to-analog converter 10 includes seven switches corresponding to a 7-bit binary input code (d06, d05, d04, d03, d02, d01, d00) and current sources connected to each switch. After the above current sources are connected in parallel, they are connected to the load R0 to generate an output voltage. The high-order bits of the input code are called the MSB (Most Significant Bit) part, and the low-order bits are called the LSB (Least Significant Bit) part. Vdd0 is the power supply voltage, and Vout0 is the voltage of the analog output. Each bit of the binary input code has only two states, 0 and 1. When in the 0 state, the corresponding switch is off, and the corresponding branch is not conducting. When in the 1 state, the corresponding switch is closed, and the current of the corresponding branch will flow through the load. Therefore, by controlling the on and off of the switch, it is determined whether the current of different current sources flows through the load, and finally an output voltage is generated.

[0033] The current sources corresponding to the MSB part of the current-steering digital-to-analog converter can be controlled in the way of thermometer code, and the current sources corresponding to the LSB part can be controlled in binary code. For example, Figure 1 As shown, the two bits d06 and d05 are the MSB part, which can be represented by a three-bit thermometer code. However, the thermometer code itself cannot solve the error of integral non-linearity. Generally speaking, the current sources corresponding to the LSB part are more accurate. Therefore, the calibration of the digital-to-analog converter is mainly aimed at the current sources of the MSB part.

[0034] Figure 2 It is a schematic structural diagram of a digital-to-analog converter according to an embodiment of the present disclosure. The digital-to-analog converter 20 exemplarily corresponds to 7-bit data, which includes a 5-bit LSB part and a 2-bit MSB part. The MSB part is converted into a three-bit thermometer code. Each bit of the MSB part and the LSB part corresponds to a branch of a current source, and the branches are connected in parallel. As Figure 2 shown, the circuit corresponding to the MSB part is the MSB module 21, and the circuit corresponding to the LSB part is the LSB module 22. The MSB part uses a three-bit thermometer code (t2, t1, t0) to represent a 2-bit binary code, and the current of each corresponding branch is 32I, where I is the unit current source. The 5 bits of the LSB part from low to high are d0, d1, d2, d3, d4, and the corresponding branch currents are 1I, 2I, 4I, 8I, 16I respectively. This embodiment adds a redundant branch as part of the LSB module 22. It is connected in parallel with other branches and can be located between the branches of the LSB module and the branches of the MSB module. It is controlled by binary code and is labeled as a5 in the figure. The current source of this branch is the same as the current source of the branch corresponding to the highest bit d4 of the corresponding LSB part, that is, 16I. The redundant branch can also use other current source values, or can include more than one branch.

[0035] The added redundant bits can provide redundancy for digital pre - distortion in the calibration of the digital - to - analog converter. By performing pre - distortion on the LSB part in the digital domain, the current - source error of the MSB module can be compensated. To perform pre - distortion calibration, first, obtain the cumulative error magnitude of the current source corresponding to each bit in the MSB module, the reference for which is Figures 3 - 5 described in detail below.

[0036] As Figure 5 shown, first, in step 51, detect the sum of the outputs of the current sources in the MSB module 21 and the output of the current source in the LSB module 22. Figure 3 And Figure 4 respectively show the circuit schematic diagrams for measuring Figure 2 the outputs of the current sources in the MSB module of the digital - to - analog converter shown.

[0037] Figure 3 The measurement circuit 23 shown includes a first current - to - voltage conversion circuit 231, a second current - to - voltage conversion circuit 232, and an analog - to - digital converter (ADC). The sum of the current sources in the LSB module 22 is input to the first current - to - voltage conversion circuit 231, which is converted into a voltage and input to the analog - to - digital converter 233 as the reference voltage Vref of the analog - to - digital converter 233. The output of one current source in the MSB module 21 is connected to the second current - to - voltage conversion circuit 232, which is converted into a voltage and input to the analog - to - digital converter 233 as the input voltage Vin of the analog - to - digital converter 233.

[0038] Figure 3 And Figure 4 have the same measurement - circuit structure. Their difference lies in measuring the outputs of two different current sources in the MSB module, where Figure 3 in the circuit shown, the current source corresponding to the first bit t0 in the MSB part is connected to the second current - to - voltage conversion circuit 232; Figure 4 in the circuit shown, the current source corresponding to the second bit t1 in the MSB part is connected to the second current - to - voltage conversion circuit 232.

[0039] By obtaining the ratio of the input voltage Vin to the reference voltage Vref, the ratio of the output of each current source in the MSB module to the sum of the outputs of the current sources in the LSB module can be obtained, which can be achieved by the analog - to - digital converter 233. Based on Figure 3 the connection method, the analog - to - digital converter 233 obtains the ratio of the current source corresponding to t0 to the sum of the current sources in the LSB module by determining the ratio of the input voltage Vin to the reference voltage Vref, denoted as P0. Based on Figure 4In the connection method, the analog-to-digital converter 233 obtains the ratio of the current source corresponding to t1 to the sum of the current sources of the LSB module by determining the ratio of the input voltage Vin to the reference voltage Vref, denoted as P1. Similarly, the current source of the highest bit of the MSB module is connected to the second current-voltage conversion circuit 232, and the converted voltage is used as the input voltage Vin of the analog-to-digital converter 233, and the ratio P2 of the current source corresponding to t2 to the sum of the current sources of the LSB module can be obtained. Under ideal conditions, P0, P1, and P2 are all 32 / 47.

[0040] In step 52, the error calculation module (not shown) of the predistortion calibration device (see Figure 7 ) calculates the cumulative error of the current source corresponding to each thermometer code in the MSB part. The cumulative error can be measured in terms of the number of copies or multiples of the unit current source. Based on P0, P1, and P2 obtained in the above manner, the cumulative error of the current source of the MSB module is calculated. Since the thermometer code of the MSB part is 3 bits, the LSB part is 6 bits, and the 6th bit is the redundant bit and has the same current as the 5th bit, which is 16I, the calculation method of the cumulative error is as follows:

[0041] G0 = P0 * 47 - 32

[0042] G1 = (P0 + P1) * 47 - 64

[0043] G2 = (P0 + P1 + P2) * 47 - 96

[0044] Round G0, G1, and G2, for example, by rounding, and convert them into binary form. G0, G1, and G2 correspond to each thermometer code (excluding the thermometer code with all bits being 0) in ascending order of the thermometer code. For example, Figures 2 - 4 In the example of, the mapping relationship between the 3-bit thermometer code and the 2-bit binary code is 00 → 000, 01 → 001, 10 → 011, 11 → 111. Then G0, G1, and G2 correspond to the thermometer codes of 001, 011, and 111 respectively.

[0045] The above method is not limited to Figure 2Instead of the 7-bit digital-to-analog converter shown, it can be used for digital-to-analog converters with various bit numbers. By using the ratio of the sum of the current sources of the MSB module to the current sources of the LSB module, the number of current shares of the actual output of the MSB module relative to the unit current can be obtained. Subtracting it from the ideal number of current shares can obtain the cumulative error corresponding to the thermometer code. Here, the current sources of the LSB module can be regarded as ideal current sources for easy calculation. If the thermometer code of the MSB part of the digital-to-analog converter is N bits and the binary code of the LSB part is M + 1 bits, where the current source size of the redundant bits included is equal to the current source size corresponding to the highest bit of the LSB part except for the redundant bits. Based on step 51, N proportional values, i.e., P0 to PN-1, will be obtained. The method for calculating the cumulative error of the current source corresponding to each thermometer code according to the N proportional values is as follows:

[0046]

[0047] where i = 0, 1, … N-1, Gi represents the cumulative error of the current source of the MSB module, and Pj is the proportional value. Each Gi corresponds to a thermometer code. For example, for the standard thermometer code, the thermometer code corresponding to Gi has all bits from the (i + 1)-th bit to the right as 1. After Gi is rounded (for example) and taken as an integer, it will be converted into binary form for application in the calibration process.

[0048] If the redundant-bit current source is different from the above example, then the in the above equation needs to be replaced with the current size of the redundant-bit current source (i.e., the number of shares or multiples relative to the unit current).

[0049] Figure 6 The flowchart shows a method for pre-distortion calibration of a digital-to-analog converter based on the cumulative error of the current source of the MSB module. The following will illustrate this method with an example of a 7-bit data digital-to-analog converter.

[0050] In step 61, the calibration module of the pre-distortion calibration device receives the binary code to be input into the digital-to-analog converter, converts the MSB part of the input signal into a thermometer code, and adds an offset to the LSB part. For Figures 2 - 4 the embodiment shown, the calibration module receives a 7-bit binary input signal (d6, d5, d4, d3, d2, d1, d0), where the MSB part is d6 and d5, and the rest is the LSB part. The 2-bit MSB part is converted into a 3-bit thermometer code (t2, t1, t0), and at the same time, the 5-bit binary code (d4, d3, d2, d1, d0) of the LSB part is added with an offset of 8 (binary is 1000) to obtain the offset binary code for the LSB part.

[0051] In step 62, it is judged whether the thermometer code is equal to 0, that is, whether the thermometer code is 000. If the judgment result is yes, in step 64, the binary code after offset is kept unchanged as the calibrated LSB part; if the judgment result is no, step 63 is executed, and the binary code of the LSB part after offset is subtracted by the cumulative error corresponding to the thermometer code as the calibrated LSB part. For example, in Figures 2 - 4 In the example shown, if the thermometer code is 001, the binary code of the LSB part after offset is subtracted by G0, that is, the result is d4d3d2d1d0 + 1000 - G0; if the thermometer code is 011, the binary code of the LSB part after offset is subtracted by G1, that is, the result is d4d3d2d1d0 + 1000 – G1; similarly, if the thermometer code is 111, the binary code becomes d4d3d2d1d0 + 1000 - G2.

[0052] In step 65, the calibration module outputs the calibrated binary code, where the LSB part of the binary code is replaced by the calibrated LSB part obtained in step 63 or step 64, and the MSB part remains unchanged. In the above method, the calibration module performs pre-distortion calibration on the LSB part, and the calibrated binary code will be used as an input signal to input to the LSB module to control the current source of the LSB module.

[0053] The above method is not limited to the digital-to-analog converter using a 7-bit binary input signal, but can be applied to digital-to-analog converters of various digits. The offset can be determined according to the maximum cumulative error, so that the binary code of the LSB part subtracted by the cumulative error will not have a negative value. In Figures 2 - 4 In the shown embodiment, when the maximum cumulative error does not exceed +7 and is not less than -8, the bias value is set to 8, which is half of the highest bit d4 of the LSB. If the cumulative error is within -4 to +3, the bias value can also be set to 4.

[0054] Due to the addition of redundant bits, for the same input binary code, there may be more than one corresponding relationship in the LSB part, that is, there may be two current control methods, which will not affect the accuracy of the output of the digital-to-analog converter.

[0055] The calibration scheme proposed by the present disclosure can significantly improve the performance of the digital-to-analog converter. Taking a 7-bit digital-to-analog converter as an example, to verify the effect of this scheme, Monte Carlo simulation was carried out under the condition that there is a 16% mismatch in the minimum current unit. Figure 8The signal-to-noise distortion ratio (SNDR) curves before and after calibration obtained by simulation are shown, where the dashed line is the SNDR curve before calibration and the solid line is the SNDR curve after calibration. Compared with before calibration, the SNDR after calibration is significantly improved, and the SNDR of the digital-to-analog converter is on average increased by about 1.8 dB. Therefore, the embodiments of the present disclosure can effectively suppress the non-linear distortion caused by the mismatch of current sources in the digital-to-analog converter.

[0056] The embodiments of the present disclosure calculate the magnitudes of the current sources of the MSB module encoded using thermometer codes, perform pre-distortion on the codewords of the LSB part in the digital domain, and use the pre-distorted codewords to control the current sources of the LSB module, thereby compensating for the errors of the current sources of the MSB module, and thus calibrating the non-linear errors of the digital-to-analog converter. The embodiments of the present disclosure adopt a digital-domain pre-distortion calibration method and device, and can improve the non-linear characteristics of the digital-to-analog converter, especially improve the integral non-linear error, without relying on complex Volterra series. At the same time, since only one current source needs to be added in the analog domain, the circuit implementation is simple and the cost is low.

[0057] Figure 7 The structural schematic diagram of a SerDes (Serializer / Deserializer) transmitter using the digital-to-analog converter of the embodiments of the present disclosure is shown. The SerDes transmitter includes a feed-forward equalizer (FFE) 71, a pre-distortion calibration device 72, a multiplexer 73, a digital-to-analog converter 74, a load 75, a clock generation module (not shown), a first frequency divider 76 and a second frequency divider 77 for providing clock signals to the feed-forward equalizer (FFE) 71, the pre-distortion calibration device 72, and the multiplexer 73.

[0058] The parallel digital signals are input to the FFE 71. The FFE 71 compensates the digital signals to suppress channel attenuation and nonlinear distortion, and sends the compensated digital signals to the predistortion calibration device 72. The predistortion calibration device 72 includes the error calculation module and the calibration module described above. The error calculation module is used to calculate the cumulative error of the current source of the most significant bit module corresponding to each thermometer code greater than 0. The calibration module performs predistortion calibration on the data to be input to the DAC, that is, calculates the least significant bit part of the calibration. The predistortion calibration device 72 can be implemented in the digital domain of the chip. The calibrated digital signals are input to the multiplexer 73. Compared with the digital signals input to the predistortion calibration device 72, the most significant bit part of the calibrated digital signals remains unchanged, and the least significant bit part is the least significant bit part of the above calibration. The multiplexer converts the calibrated digital signals from parallel digital signals into serial digital signals for transmission to the digital-to-analog converter. Specifically, the multiplexer 73 may include one or a cascade of multiple multiplexers to convert parallel digital signals into a high-speed serial digital signal. For example, the input 64-way parallel digital signals can be gradually generated into a serial digital signal via a 64:4 multiplexer and a 4:1 multiplexer.

[0059] The digital-to-analog converter 74 receives the serial digital signal and converts it into an analog signal. The digital-to-analog converter 74 can use a digital-to-analog converter including the redundant current source and the measurement module in the above embodiments of the present disclosure. For example, refer to Figures 2 - 6 the digital-to-analog converter described, and feedback the measurement result of the measurement module to the predistortion calibration device 72, so that the predistortion calibration device 72 realizes the predistortion calibration of the signal to be input to the digital-to-analog converter.

[0060] The load 75 is connected to the output end of the SerDes transmitter to reduce reflection and signal attenuation. For example, the output end can adopt a common 50Ω matching impedance.

[0061] The clock signals of each part of the SerDes transmitter can be provided by a clock generation circuit. The main clock signal driving the digital-to-analog converter is divided by the first frequency divider 76 and then input to the multiplexer 73; subsequently, the signal is further divided by the second frequency divider 77 and provided to the FFE 71 and the predistortion calibration device 72. It should be noted that the clock signal providing method of the SerDes transmitter is not limited to this, and an independent clock circuit can also be used to provide clock signals for one or more modules respectively.

[0062] The above is only an exemplary embodiment of the present disclosure, and is not used to limit the protection scope of the present disclosure. The protection scope of the present disclosure is determined by the appended claims.

Claims

1. A pre-distortion calibration device for a digital-to-analog converter, used for a serializer / deserializer transmitter, characterized in that, Comprising: An error calculation module, which calculates the cumulative error of the current source corresponding to each thermometer code greater than 0 used by the most significant bit module of the digital-to-analog converter according to the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module; A calibration module, which adds a predetermined offset to the least significant bit part of the data to be input to the digital-to-analog converter and calculates the calibrated least significant bit part according to the cumulative error corresponding to the thermometer code of the most significant bit part of the data to be input; Wherein the most significant bit module of the digital-to-analog converter is controlled using thermometer codes, and the least significant bit module is controlled using binary codes. The least significant bit module includes a redundant branch, which includes current sources of the redundant branch.

2. The predistortion calibration device according to claim 1, wherein The predetermined offset is determined according to the maximum cumulative error.

3. The predistortion calibration device according to claim 1, wherein The error calculation module calculates the number of current portions of the output of the most significant bit module relative to the unit current according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module, and the difference between it and the ideal number of current portions corresponding to the thermometer code is used as the cumulative error.

4. The predistortion calibration device according to claim 1, wherein The error calculation module calculates the cumulative error of the current source corresponding to each thermometer code greater than 0 of the most significant bit module of the digital-to-analog converter through the following equation: ， Where N is the number of bits of the thermometer code corresponding to the most significant bit module, M + 1 is the number of bits of the binary code corresponding to the least significant bit module, i = 0, 1, … N - 1, Gi represents the cumulative error of the current source of the most significant bit module, Pj is the ratio between the output of the jth current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module. The least significant bit module includes a redundant branch, and the current magnitude of its current source is the same as that of the current source corresponding to the highest bit of the least significant bit part except the redundant branch.

5. The predistortion calibration device according to claim 1 or 3, characterized in that The calculation of the calibrated least significant bit part includes subtracting the cumulative error corresponding to the thermometer code from the least significant bit part of the data to be input with the predetermined offset added when the thermometer code of the most significant bit part of the data to be input is greater than 0.

6. The predistortion calibration device according to claim 1, characterized in that The digital-to-analog converter includes a measurement module for measuring the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module. The measurement module includes a first current-voltage conversion circuit, a second current-voltage conversion circuit and an analog-to-digital converter. The first current-voltage conversion circuit receives the outputs of all current sources in the least significant bit module, and its output voltage serves as the reference voltage of the analog-to-digital converter; the second current-voltage conversion circuit is connected to a current source in the most significant bit module, and its output voltage serves as the input voltage of the analog-to-digital converter. The analog-to-digital converter outputs the ratio of the input voltage to the reference voltage.

7. A pre-distortion calibration method for a digital-to-analog converter, which is used for a serializer / deserializer transmitter, is characterized in that Comprising Measure the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module, where the most significant bit module is controlled using a thermometer code and the least significant bit module is controlled using a binary code, and the least significant bit module includes redundant branches, which include current sources of the redundant branches; Calculate the cumulative error of the current source of the most significant bit module corresponding to each thermometer code greater than 0 according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module; Add a predetermined offset to the least significant bit part of the data to be input to the digital-to-analog converter, and calculate the calibrated least significant bit part according to the cumulative error corresponding to the thermometer code of the most significant bit part of the data to be input; 8. The pre-distortion calibration method for a digital-to-analog converter according to claim 7, characterized in that The ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module includes inputting the sum of the outputs of all current sources in the least significant bit module to an analog-to-digital converter after conversion by a first current-voltage conversion circuit as its reference voltage, and inputting the output of one current source in the most significant bit module to the analog-to-digital converter after conversion by a second current-voltage conversion circuit as its input voltage, and the analog-to-digital converter outputs the ratio of the input voltage to the reference voltage; 9. The pre-distortion calibration method for a digital-to-analog converter according to claim 7, characterized in that Calculate the number of current portions of the output of the most significant bit module relative to the unit current according to the ratio between the output of each current source in the most significant bit module and the sum of the outputs of all current sources in the least significant bit module for each thermometer code, and the difference between it and the ideal number of current portions corresponding to the thermometer code is used as the cumulative error; 10. The pre-distortion calibration method for a digital-to-analog converter according to any one of claims 7-9, characterized in that The calculation of the calibrated least significant bit part includes subtracting the cumulative error corresponding to the thermometer code from the least significant bit part of the data to be input with the predetermined offset added when the thermometer code of the most significant bit part of the data to be input is greater than 0; 11. The pre-distortion calibration method for a digital-to-analog converter according to claim 7, characterized in that The current magnitude of the current source of the redundant branch is the same as the current source corresponding to the most significant bit of the least significant bit part other than the redundant branch; 12. A serializer / deserializer transmitter, characterized in that Including a feed-forward equalizer, a predistortion calibration device as described in any one of claims 1-6, a multiplexer, and a digital-to-analog converter connected in sequence, the serializer / deserializer transmitter further includes a clock generation circuit, which provides corresponding clock signals for the feed-forward equalizer, the predistortion calibration device, the multiplexer, and the digital-to-analog converter, where the digital-to-analog converter includes a measurement module, which measures the ratio between the output of each current source in the most significant bit module of the digital-to-analog converter and the sum of the outputs of all current sources in the least significant bit module; 13. The serializer / deserializer transmitter according to claim 12, wherein The predistortion calibration device receives the digital signal output by the feed-forward equalizer and outputs the calibrated digital signal to the multiplexer. Compared with the digital signal received by the predistortion calibration device, its most significant bit part remains unchanged, and the least significant bit part is the calibrated least significant bit part;

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