Static error calibration system and method for current-steering digital-to-analog converter

Abstract

The invention discloses a static error calibration system and method for a current-steering digital-to-analog converter, and relates to the technical field of circuits, and the system comprises a current-steering digital-to-analog converter module, a measurement system and a control system. The current steering type digital-to-analog converter module comprises a plurality of current steering type digital-to-analog converter units, and each current steering type digital-to-analog converter unit comprises a plurality of compensation digital-to-analog converter units; the measuring system is used for measuring the output current or load voltage of the current-steering digital-to-analog converter module; and the control system is used for calibrating the current steering digital-to-analog converter module according to the output current or the load voltage measured by the measurement system and the control signal. According to the compensation digital-to-analog converter unit, the field-effect tube of the same type as the first current source tube is used, so that the temperature excursions of the first current source tube and the field-effect tube are similar, and errors can be reduced. Meanwhile, the static current of each input bit can be adjusted, so that the current source tubes are mutually proportional, the compensation range can be expanded, and the compensation precision is high.

Description

Technical Field

[0001] The present application relates to the field of circuit technology, and in particular to a static error calibration system and method for a current-steering digital-to-analog converter. Background Art

[0002] Digital-to-analog converters are an important part of signal processing systems, audio systems, automotive electronic systems, etc. Their research background is rooted in the demand for more efficient and accurate conversion between digital and analog signals, and is closely related to the society's growing need for high-quality digital signal processing. In these scenarios, digital-to-analog converters are often required to accurately convert digital signals into analog signals. However, due to the inevitable mismatch introduced during the process manufacturing process, such as uneven doping or size mismatch, the digital-to-analog converter has output errors. Summary of the invention

[0003] The main purpose of the embodiments of the present application is to provide a static error calibration system and method for a current-steering digital-to-analog converter to reduce the output error of the current-steering digital-to-analog converter.

[0004] To achieve the above-mentioned purpose, an embodiment of the present application provides a static error calibration system of a current-steering digital-to-analog converter in one aspect, wherein the calibration system includes a current-steering digital-to-analog converter module, a measurement system, and a control system;

[0005] Wherein, the current-steering digital-to-analog converter module includes a plurality of current-steering digital-to-analog converter units, and each of the current-steering digital-to-analog converter units includes a plurality of compensation digital-to-analog converter units;

[0006] The current steering type digital-to-analog converter unit includes a resistor ladder, a first switch tube, a cascode tube and a first current source tube; the resistor ladder is provided with a first differential output terminal and a second differential output terminal, and the first switch tube is provided with a first differential input terminal and a second differential input terminal; the first switch tube and the cascode tube are connected to the resistor ladder and the first current source tube respectively; the first current source tube is also connected to a reference ground;

[0007] The compensation digital-to-analog converter unit includes a second switch tube and a second current source tube; the second switch tube is respectively provided with an input end and an output end of the compensation digital-to-analog converter unit, the second switch tube is connected to the second current source tube, and the second current source tube is also connected to a reference ground;

[0008] The output ends of the plurality of compensation digital-to-analog converter units are connected to the common connection end of the first switch tube and the common-source common-gate tube and the first current source tube;

[0009] The measurement system is used to measure the output current or load voltage of the current-steering digital-to-analog converter module;

[0010] The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage and the control signal measured by the measurement system.

[0011] In some embodiments, one of the current-steering DAC units includes one of the compensation DAC units or a plurality of the compensation DAC units;

[0012] Wherein, when one of the current steering type digital-to-analog converter units includes one of the compensation digital-to-analog converter units, the output end of the compensation digital-to-analog converter unit is connected to the first switch tube and the common connection end of the common source tube and the first current source tube;

[0013] When one of the current-steering digital-to-analog converter units includes a plurality of the compensation digital-to-analog converter units, the output end of each of the compensation digital-to-analog converter units is connected to the first switch tube and the common connection end of the common-source common-gate tube and the first current source tube.

[0014] In some embodiments, when one of the current steering digital-to-analog converter units includes a plurality of the compensation digital-to-analog converter units, each of the compensation digital-to-analog converter units includes one of the second switching transistors, and each of the compensation digital-to-analog converter units includes two i the second current source tube;

[0015] Wherein, i is an integer ranging from 0 to n, and n represents the total number of the compensation digital-to-analog converter units, and the number of the second current source tubes in each of the compensation digital-to-analog converter units is different.

[0016] In some embodiments, the compensation digital-to-analog converter unit includes a single-ended output type or a differential output type;

[0017] When the compensation digital-to-analog converter unit adopts the single-ended output type, the single-ended output end of the second switch tube in a plurality of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube; the second switch tubes in a plurality of the compensation digital-to-analog converter units are respectively provided with single-ended input ends;

[0018] When the compensation digital-to-analog converter unit adopts the differential output type, the first differential output end of the second switch tube in several of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube, and the second differential output ends of the second switch tube in several of the compensation digital-to-analog converter units are respectively connected to the power supply; the second switch tubes in several of the compensation digital-to-analog converter units are respectively provided with a first differential input end and a second differential input end.

[0019] In some embodiments, the measurement system employs a transimpedance amplifier;

[0020] The transimpedance amplifier is used to measure the output current of the current-steering digital-to-analog converter module, and then output a voltage corresponding to the output current.

[0021] In some embodiments, the measurement system and the control system are integrated inside the current-steering digital-to-analog converter module;

[0022] Alternatively, the measurement system and the control system are arranged outside the current-steering digital-to-analog converter module.

[0023] In some embodiments, the calibration system further includes a host computer;

[0024] The host computer is used to output the control signal;

[0025] The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage measured by the measurement system and the control signal output by the host computer.

[0026] To achieve the above object, another aspect of an embodiment of the present application provides a static error calibration method for a current-steering digital-to-analog converter. The calibration method is applied to a static error calibration system for a current-steering digital-to-analog converter as described in the present application. The calibration method comprises the following steps:

[0027] Performing gain calibration on the current-steering digital-to-analog converter module so that the compensation current does not exceed the coverage range of the compensation digital-to-analog converter unit in the current-steering digital-to-analog converter module;

[0028] Perform nonlinear calibration on the current-steering DAC module to reduce differential nonlinearity and integral nonlinearity;

[0029] The step of performing gain calibration on the current-steering digital-to-analog converter module is performed again to reduce the gain error introduced by the nonlinear calibration.

[0030] In some embodiments, the gain calibration of the current-steering digital-to-analog converter module comprises the following steps:

[0031] Turning off all the compensation DAC units in the current-steering DAC module;

[0032] placing the compensation digital-to-analog converter unit of the reference current source at an intermediate codeword;

[0033] Measuring a first output full-scale current of the current-steering digital-to-analog converter module;

[0034] increasing or decreasing an input bit of the compensation digital-to-analog converter unit to adjust an output of the compensation digital-to-analog converter unit;

[0035] Measuring a second output full-scale current of the current-steering digital-to-analog converter module;

[0036] Calculating a gain error based on the first output full-scale current and the second output full-scale current;

[0037] If the gain error becomes smaller, return to the step of increasing or decreasing the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit until the gain error reaches a minimum value, decrease or increase the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit, and then end the calibration;

[0038] If the gain error increases or remains unchanged, the input bit of the compensation DAC unit is reduced or increased to adjust the output of the compensation DAC unit until the gain error reaches a minimum value, and then the calibration is terminated.

[0039] In some embodiments, the nonlinear calibration of the current-steering digital-to-analog converter module comprises the following steps:

[0040] Calculate the equivalent current of each current-steering digital-to-analog converter unit in the current-steering digital-to-analog converter module; wherein each equivalent current includes the output current of the corresponding current-steering digital-to-analog converter unit when the thermometer code is controlled and the output current of the corresponding current-steering digital-to-analog converter unit when the binary code is controlled;

[0041] Determine the maximum value among the equivalent currents as the standard current value;

[0042] The compensation DAC unit of the thermometer code is adjusted so that the output current of the current steering DAC unit is consistent with NI STD The difference between them is minimized; where N is a positive integer, I STD Indicates the standard current value;

[0043] The compensation digital-to-analog converter unit of the binary code is adjusted so that the output current of the current-steering digital-to-analog converter unit is The difference between them is minimized; where M is a positive integer.

[0044] The embodiments of the present application include at least the following beneficial effects:

[0045] The calibration system of the present application includes a current-steering digital-to-analog converter module, a measurement system, and a control system; the current-steering digital-to-analog converter module includes a plurality of current-steering digital-to-analog converter units, and each current-steering digital-to-analog converter unit includes a plurality of compensation digital-to-analog converter units; the measurement system is used to measure the output current or load voltage of the current-steering digital-to-analog converter module; the control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or load voltage and the control signal measured by the measurement system. The present application is not limited by the segmented architecture of the compensation digital-to-analog converter by providing an independent compensation digital-to-analog converter unit for the first current source tube of each current-steering digital-to-analog converter unit, and the compensation digital-to-analog converter unit uses the same type of field effect tube as the first current source tube, so that the temperature drift of the above two is similar, which can reduce the error. At the same time, the present application can adjust the static current of each input bit so that the current source tubes are proportional to each other, and can also expand the compensation range with high compensation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 An example structural diagram of a CSDAC unit provided in an embodiment of the present application;

[0048] Figure 2 An example diagram of an optional 14-bit CSDAC architecture provided in an embodiment of the present application;

[0049] Figure 3 A schematic diagram of the structure of a static error calibration system for a current-steering digital-to-analog converter provided in an embodiment of the present application;

[0050] Figure 4 A schematic flow chart of a static error calibration method for a current-steering digital-to-analog converter provided in an embodiment of the present application;

[0051] Figure 5 A schematic diagram of a CSDAC unit with a CALDAC unit provided in an embodiment of the present application;

[0052] Figure 6 A schematic diagram of a CALDAC unit provided in an embodiment of the present application;

[0053] Figure 7 A schematic diagram of a differential CALDAC unit provided in an embodiment of the present application;

[0054] Figure 8 A schematic diagram of a single-ended CALDAC unit provided in an embodiment of the present application;

[0055] Fig. 9 A schematic diagram of a 3-bit CALDAC unit provided in an embodiment of the present application;

[0056] Fig.10 A schematic diagram of a CSDAC unit with a CALDAC unit provided in an embodiment of the present application;

[0057] Fig.11 An exemplary structural diagram of a calibration system provided in an embodiment of the present application;

[0058] Fig.12 A schematic diagram of a more specific calibration system provided in an embodiment of the present application;

[0059] Fig.13 A flow chart of a calibration method provided in an embodiment of the present application.

[0060] Fig.14 A first gain calibration flow chart provided in an embodiment of the present application;

[0061] Fig.15 A schematic diagram of a transmission characteristic curve and an endpoint fitting curve before and after the first gain calibration provided in an embodiment of the present application;

[0062] Fig.16 A nonlinear calibration flow chart provided in an embodiment of the present application;

[0063] Fig.17 A schematic diagram of a transmission characteristic curve before and after nonlinear calibration provided in an embodiment of the present application;

[0064] Fig.18 A second gain calibration flow chart provided in an embodiment of the present application;

[0065] Fig.19 A schematic diagram of a transmission characteristic curve before and after the second gain calibration provided in an embodiment of the present application;

[0066] Fig. 20 A schematic diagram of a transmission characteristic curve after a round of calibration provided in an embodiment of the present application. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the embodiments of the present application. They are only examples of devices and methods consistent with some aspects of the embodiments of the present application as detailed in the attached claims.

[0068] It is understood that the terms "first", "second", etc. used in this application can be used to describe various concepts in this article, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another concept. For example, without departing from the scope of the embodiment of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" and "if" as used herein can be interpreted as "at the time of" or "when" or "in response to determination".

[0069] The terms "at least one", "multiple", "each", "any", etc. used in this application, at least one includes one, two or more, multiple includes two or more, each refers to each of the corresponding multiple, and any refers to any one of the multiple.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0071] Before describing the embodiments of the present application in detail, some terms and related technologies involved in the embodiments of the present application are first described as follows:

[0072] DAC, digital-to-analog converter: A chip that converts input bit signals (digital signals) into analog signals. In this article, it mainly refers to the DAC core module, which mainly includes three parts: switch tube, cascode tube, current source tube, and may also include a resistor ladder to shunt current.

[0073] CSDAC, current steering DAC, current steering digital-to-analog converter, is a type of digital-to-analog converter composed of similar CSDAC units.

[0074] CALDAC, calibration DAC, compensation DAC: used to provide compensation current.

[0075] The static performance of DAC is generally described by these four parameters, namely gain error, offset error, differential nonlinearity, and integral nonlinearity. The smaller the values ​​of these parameters, the better the static performance.

[0076] Gain error: The percentage of the full-scale current output by the actual DAC relative to the standard full-scale current.

[0077] Offset error: The percentage of the actual DAC output relative to the standard full-scale current when the input is zero. It is related to the leakage current when the switch tube is in the cut-off region.

[0078] Differential Nonlinearity, DNL: The difference between the output difference of adjacent codewords and the ideal step height (1LSB).

[0079] Integral Nonlinearity, INL: The difference between the actual output value and the ideal converter output value.

[0080] Least Significant Bit, LSB, Least Significant Bit: The unit of INL and DNL. LSB represents the output current of the lowest bit in the DAC or the voltage value it generates on the load. For example, for a 16-bit precision DAC, assuming the full-scale voltage V ref =1V, then LSB can also represent the lower few bits of binary code control.

[0081] The dynamic performance of a DAC: or the dynamic range of a DAC, can be described by parameters such as the spurious-free dynamic range (SFDR).

[0082] Front-end calibration: Calibrate after the chip is powered on.

[0083] Background calibration: Calibrate the chip while it is working.

[0084] DAC resolution: The number of bits of digital code in the DAC input indicates the number of bits of DAC resolution.

[0085] DAC segmented architecture: For example, for a 14-bit DAC, the upper 4 bits use thermometer code and the lower 10 bits use binary code, which is a segmented architecture. For binary code control, each bit controls one CSDAC unit; for thermometer code control, k bits control 2 k -1 unit.

[0086] IFSR, current of full scale range, output full-scale current: refers to the maximum output current of the DAC.

[0087] The transfer function or transfer characteristic curve of DAC: the horizontal axis represents the input bits of the DAC (i.e., the digital code), and the vertical axis is generally the DAC output current or load voltage, which is an analog quantity.

[0088] TIA, trans-impedance amplifier, is used to convert current input into voltage output.

[0089] SPI: Serial Peripheral Interface, serial peripheral interface.

[0090] DAC is an important component of signal processing systems, audio systems, automotive electronic systems, etc. Its research background is rooted in the demand for more efficient and accurate conversion between digital and analog signals, and is closely related to the society's growing need for high-quality digital signal processing. In these scenarios, DAC is often required to accurately convert digital signals into analog signals. However, due to the inevitable mismatch introduced during the process manufacturing process, such as uneven doping or size mismatch, errors in DAC output occur. The errors are mainly reflected in time and amplitude. For medium and low frequency DACs, the amplitude error is more significant than the time error. The amplitude error deteriorates the static performance of the DAC, affects the linearity of the DAC, may cause harmonic distortion, and thus affect the dynamic performance.

[0091] CSDAC has the characteristics of high speed and easy integration, and its output current can directly drive the load or power amplifier, so it is widely used. Figure 1 As shown in Figure 1, a CSDAC basic unit with differential output includes several parts such as switch tube, common source and common gate tube, current source tube, and may also include a resistor ladder. A possible DAC architecture with differential output is shown in Figure 1. Figure 2 As shown in the figure, the binary code and the thermometer code are 4 bits and 10 bits respectively. In fact, the number of bits of the binary code and the thermometer code may be arbitrary.

[0092] Existing calibration schemes mostly use CALDAC to compensate for static current to calibrate the output of CSDAC, and resist the influence of temperature and aging through background calibration. However, the power consumption is large, the process is complex, and the implementation is difficult. Similarly, the solution of this patent also uses CALDAC to compensate for static output current, but adopts foreground calibration, that is, calibration after each power-on, which can reduce power consumption, and the calibration result has small error and the calibration process is simpler.

[0093] Reference Figure 3 , an embodiment of the present application provides a static error calibration system for a current-steering digital-to-analog converter, the calibration system comprising a current-steering digital-to-analog converter module, a measurement system, and a control system;

[0094] Wherein, the current-steering digital-to-analog converter module includes a plurality of current-steering digital-to-analog converter units, and each of the current-steering digital-to-analog converter units includes a plurality of compensation digital-to-analog converter units;

[0095] The current steering type digital-to-analog converter unit includes a resistor ladder, a first switch tube, a cascode tube and a first current source tube; the resistor ladder is provided with a first differential output terminal and a second differential output terminal, and the first switch tube is provided with a first differential input terminal and a second differential input terminal; the first switch tube and the cascode tube are connected to the resistor ladder and the first current source tube respectively; the first current source tube is also connected to a reference ground;

[0096] The compensation digital-to-analog converter unit includes a second switch tube and a second current source tube; the second switch tube is respectively provided with an input end and an output end of the compensation digital-to-analog converter unit, the second switch tube is connected to the second current source tube, and the second current source tube is also connected to a reference ground;

[0097] The output ends of the plurality of compensation digital-to-analog converter units are connected to the common connection end of the first switch tube and the common-source common-gate tube and the first current source tube;

[0098] The measurement system is used to measure the output current or load voltage of the current-steering digital-to-analog converter module;

[0099] The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage and the control signal measured by the measurement system.

[0100] As an optional implementation, one of the current-steering digital-to-analog converter units includes one of the compensation digital-to-analog converter units or a plurality of the compensation digital-to-analog converter units;

[0101] Wherein, when one of the current steering type digital-to-analog converter units includes one of the compensation digital-to-analog converter units, the output end of the compensation digital-to-analog converter unit is connected to the first switch tube and the common connection end of the common source tube and the first current source tube;

[0102] When one of the current-steering digital-to-analog converter units includes a plurality of the compensation digital-to-analog converter units, the output end of each of the compensation digital-to-analog converter units is connected to the first switch tube and the common connection end of the common-source common-gate tube and the first current source tube.

[0103] Further, when one of the current steering type digital-to-analog converter units includes a plurality of the compensation digital-to-analog converter units, each of the compensation digital-to-analog converter units includes one of the second switching tubes, and each of the compensation digital-to-analog converter units includes two i the second current source tube;

[0104] Wherein, i is an integer ranging from 0 to n, and n represents the total number of the compensation digital-to-analog converter units, and the number of the second current source tubes in each of the compensation digital-to-analog converter units is different.

[0105] As another optional implementation, the compensation digital-to-analog converter unit includes a single-ended output type or a differential output type;

[0106] When the compensation digital-to-analog converter unit adopts the single-ended output type, the single-ended output end of the second switch tube in a plurality of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube; the second switch tubes in a plurality of the compensation digital-to-analog converter units are respectively provided with single-ended input ends;

[0107] When the compensation digital-to-analog converter unit adopts the differential output type, the first differential output end of the second switch tube in several of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube, and the second differential output ends of the second switch tube in several of the compensation digital-to-analog converter units are respectively connected to the power supply; the second switch tubes in several of the compensation digital-to-analog converter units are respectively provided with a first differential input end and a second differential input end.

[0108] Optionally, the measurement system uses a transimpedance amplifier;

[0109] The transimpedance amplifier is used to measure the output current of the current-steering digital-to-analog converter module, and then output a voltage corresponding to the output current.

[0110] Optionally, the measurement system and the control system are integrated inside the current-steering digital-to-analog converter module;

[0111] Alternatively, the measurement system and the control system are arranged outside the current-steering digital-to-analog converter module.

[0112] Furthermore, the calibration system also includes a host computer;

[0113] The host computer is used to output the control signal;

[0114] The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage measured by the measurement system and the control signal output by the host computer.

[0115] Reference Figure 4 The present application also provides a static error calibration method for a current-steering digital-to-analog converter. The calibration method is applied to a static error calibration system for a current-steering digital-to-analog converter of the present application. The calibration method includes steps S400 to S420:

[0116] S400: performing gain calibration on the current-steering digital-to-analog converter module so that the compensation current does not exceed the coverage range of the compensation digital-to-analog converter unit in the current-steering digital-to-analog converter module;

[0117] S410: performing nonlinear calibration on the current-steering digital-to-analog converter module to reduce differential nonlinearity and integral nonlinearity; wherein the nonlinear calibration is to reduce differential nonlinearity (DNL) and integral nonlinearity (INL), and DNL and INL are two indicators of DAC;

[0118] S420: Execute the step of performing gain calibration on the current-steering digital-to-analog converter module again to reduce the gain error introduced by the nonlinear calibration.

[0119] As a further implementation, step S400 may include steps S401 to S408:

[0120] S401: Turn off all the compensation digital-to-analog converter units in the current-steering digital-to-analog converter module;

[0121] S402: placing the compensation digital-to-analog converter unit of the reference current source in an intermediate codeword;

[0122] S403: measuring a first output full-scale current of the current-steering digital-to-analog converter module;

[0123] S404: increasing or decreasing an input bit of the compensation digital-to-analog converter unit to adjust an output of the compensation digital-to-analog converter unit;

[0124] S405: measuring a second output full-scale current of the current-steering digital-to-analog converter module;

[0125] S406: Calculating a gain error according to the first output full-scale current and the second output full-scale current;

[0126] S407: If the gain error becomes smaller, return to the step of increasing or decreasing the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit, until the gain error reaches a minimum value, decrease or increase the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit, and then end the calibration;

[0127] S408: If the gain error increases or remains unchanged, reduce or increase the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit until the gain error reaches a minimum value, and then end the calibration.

[0128] As a further implementation, step S410 may include steps S411 to S414:

[0129] S411: Calculate the equivalent current of each current-steering digital-to-analog converter unit in the current-steering digital-to-analog converter module; wherein each equivalent current includes the output current of the corresponding current-steering digital-to-analog converter unit when the thermometer code is controlled and the output current of the corresponding current-steering digital-to-analog converter unit when the binary code is controlled.

[0130] Specifically, this embodiment calculates the output current of each of the current steering type DAC units, including the current steering DAC units controlled by the thermometer code and the binary code, and each current steering type DAC unit is equivalent to a thermometer code size. For example, a 14-bit DAC has a 4-bit thermometer code + a 10-bit binary code, and the 14 bits are represented by D13-D0 from high to low, D13-D10 is the thermometer code, and D9-D0 is the binary code. If D0 controls the current source output to be I D0 , then the equivalent current is I STD0 =2 10 I D0 ; If D1 controls the current source output to be I D1 , then the equivalent current is I STD1 =2 9 I D1 , and so on; D13-D10 controls a total of 2 4 -1=15, the thermometer code does not need to be multiplied by weight, which are I SRD10 ~I STD25 , the standard current value is defined as I STD =max{I STDn},n=0~25.

[0131] S412: Determine the maximum value among the equivalent currents as the standard current value.

[0132] S413: Adjust the compensation digital-to-analog converter unit of the thermometer code so that the output current of the current-steering digital-to-analog converter unit is consistent with NI STD The difference between them is minimized; where N is a positive integer, I STD Indicates the standard current value;

[0133] S414: Adjust the compensation digital-to-analog converter unit of the binary code so that the output current of the current-steering digital-to-analog converter unit is equal to The difference between them is minimized; where M is a positive integer.

[0134] For example, in S411, the calibration is performed with I STD As a reference, adjust the compensation DAC unit so that I D0 Towards Close, I D1 Towards Close, and so on; for the thermometer code, the compensation digital-to-analog converter unit is adjusted so that I D10 To I STD Close, I D11 +I D10 To 2I STD Close, I D12 +I D11 +I D10 To 3I STD Closer, and so on.

[0135] Therefore, the adjustment step may specifically be: adjusting the thermometer code compensation digital-to-analog converter unit so that the current steering digital-to-analog converter unit outputs a current to NI STD Close to, adjust the binary code compensation DAC unit so that the current steering DAC unit outputs current to Close; N and M are positive integers depending on the specific segmentation architecture.

[0136] Next, the solution of the embodiment of the present application will be introduced and explained in detail with reference to specific application examples.

[0137] In order to solve the problem of amplitude error in the output of the CSDAC, this embodiment proposes a relatively simple solution that can effectively reduce Gain error, INL and DNL.

[0138] Specifically, this embodiment may include the following technical solutions:

[0139] Add a CALDAC to each CSDAC unit, such as Figure 5 A CALDAC unit can have a similar structure to a CSDAC unit. Figure 6As shown, the CALDAC unit should have a switch tube and a current source tube. The high and low levels of the input bits control the on or off of the switch tube, and the current source tube provides compensation current for the CSDAC unit. The switch tube may have a differential input 310 or a single-ended input 320. The CALDAC may have a differential output 330 or a single-ended output 340. The input of the CALDAC should have multiple bits, and the number of CALDAC units controlled by each bit is equal to the weight of the bit, so that it can output a certain range of current. Assume that the CALDAC has n-bit input, such as Figure 7 As shown, CD0 represents the lowest bit and controls one CALDAC unit; CD1 represents the second highest bit and controls two; and so on CDn controls two n CALDAC units. Figure 7 , Figure 8 The schematic diagrams of differential and single-ended CALDAC are shown respectively. The specific number of bits and the current output of the minimum bit should be determined according to the simulation situation. Switches of the same bit can be shared. Figure 5 , Figure 5 Includes schematics for the CSDAC cell with either a differential or single-ended CALDAC. Fig. 9 A possible implementation of a 3-bit CALDAC is shown. Fig. 9 Among them, M1-M7 are current source tubes, M8-M10 are switch tubes, M2-M3 share the switch tube M9, and M4-M7 share the switch tube M10. The current source tube of CALDAC should be of the same type as the current source tube of CSDAC and use the same bias voltage. Fig.10 An implementation of a CSDAC unit with CALDAC is shown, where Vb is the bias voltage of all current source tubes.

[0140] Fig.11 is an example structure diagram of the calibration system. In addition to the CSDAC to be calibrated, the calibration system can also include a measurement system and a control system. The measurement system is used to measure the output current or load voltage of the CSDAC, and its input is the output of the CSDAC. The control system is used to control the calibration process, including controlling the input bits of the CSDAC and each CALDAC, and its input signal includes the output of the measurement system and some necessary control signals. The measurement system and the control system can be placed inside the CSDAC chip or outside the chip. A more specific calibration system such as Fig.12 As shown, using TIA can obtain more accurate measurement results, and the control system can interact with the host computer through SPI signals.

[0141] The output current of the CSDAC unit is copied from the reference current source. Generally speaking, all CSDAC units use the same reference current source. In some cases, the units controlled by the thermometer code and the units controlled by the binary code can each use a reference current source. By adding CALDAC to the reference current source, the output full-scale current can be adjusted and the gain error can be calibrated.

[0142] A round of calibration is performed on the CSDAC unit using the same reference current source. A round of calibration includes three steps, namely gain calibration, nonlinear calibration, and gain calibration. Fig.13 The first gain calibration process is as follows Fig.14 As shown, the first gain calibration is to ensure that the compensation current does not exceed the coverage range of CALDAC during the subsequent nonlinear calibration. The CALDAC of the reference current source is placed at the intermediate codeword 1210 (assuming that the input of CALDAC is CD3-CD0, the intermediate codeword is 100b), and the CALDAC output 1220 is adjusted by increasing (or decreasing) the input bit of CALDAC. Generally speaking, the adjustment is made in one direction, that is, either increasing the input bit or decreasing the input bit. The transfer function diagram before and after calibration is shown in Fig.15 The slope of the transfer characteristic curve end point fitting is the gain. In this process, the gain is calibrated to the standard value, reducing the gain error. However, the nonlinearity is not improved, and the integral nonlinearity and differential nonlinearity are still large, which is manifested as uneven step heights in the transfer function.

[0143] The nonlinear calibration process is as follows Fig.16 As shown, Fig.16 The dashed box shows Figure 2 This process improves nonlinearity but introduces gain error, and the introduced gain error is definitely too large. Here, "equivalent current" is defined as the output current of a CSDAC unit controlled by the thermometer code. Figure 2 Taking the architecture shown in the figure as an example, D13-D10 is the thermometer code. When the input of D13-D10 is 0001b, it controls one CSDAC unit and the output is I M1 ; When the input of D13-D10 is 0010b, it controls 2 CSDAC units and the output is I M1 +I M2 I M1 and I M2 All of them represent the size of the equivalent current; the rest of the input bits are analogous. D9-D0 is a binary code. When D9-D0 = 1000_0000_00b, only the CSDAC output controlled by D9 is output. D9 is 1 bit lower than D10. The output current size is I9, so the equivalent current is 2 1I9; when the input is shifted right by one bit, that is, D9-D0=0100_0000_00b, only the CSDAC output controlled by D8 is output, D8 is 2 bits lower than D10, and the output current is I8, then the equivalent current is 2 2 I8; and so on. The maximum value among all equivalent currents is used as the calibration standard value I STD , adjust the CALDAC input bits so that the equivalent output current of each CSDAC is closest to I STD .

[0144] The methods for calibrating thermometer code and binary code controlled units are slightly different. First calibrate the thermometer code. The first CALDAC calibrates the output of one CSDAC unit. The second CALDAC calibrates the output of the first two CSDAC units. The third CALDAC calibrates the first three CSDAC units, and so on. This can calibrate the integral nonlinearity. Then calibrate the binary code. The CALDAC in the CSDAC unit only calibrates the deviation of its own output current. In this process, there are several CSDACs that need to be calibrated several times. Figure 2 As an example, there are (2 4 -1)+10=25 CSDAC units, that is, there are 25 CALDACs in total, and calibration is required 25 times. Considering that low bits are easily submerged by noise, the calibration of the lowest 2-4 binary codes to control the CSDAC unit can be abandoned according to the actual measurement situation. For example, Fig.17 It is a schematic diagram of the transmission characteristic curve before and after nonlinear calibration.

[0145] The second gain calibration process is as follows Fig.18 As shown, similar to the first gain calibration process, Fig.19 Figure 1 is a schematic diagram of the transfer characteristic curve before and after the second gain calibration. After the second gain calibration, the gain error, integral nonlinearity and differential nonlinearity are greatly improved, and the calibration of static parameters is completed. After completing a round of calibration process, the transfer function is characterized by uniform step height, and theoretically all points on the step will fall on the standard gain curve, such as Fig. 20 In summary, the beneficial effects of this embodiment include:

[0146] 1. Provide an independent CALDAC for each current source tube, which is not limited by the CSDAC segment architecture.

[0147] 2. Since CALDAC uses the same type of MOSFET as the current source tube, CALDAC and the current source tube can have similar temperature drift, so that the temperature changes during operation but the output static current of each CSDAC unit remains proportional.

[0148] 3. Since this embodiment is foreground calibration, power consumption can be reduced.

[0149] 4. Effectively reduce the static error of DAC: the static current of each bit can be adjusted so that the current sources are proportional to each other, and at the same time the compensation range can be expanded with high compensation accuracy.

[0150] 5. Matching between CSDACs may not be required, simplifying the difficulty of layout when drawing the layout.

[0151] The embodiments described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application and do not constitute a limitation on the technical solutions provided in the embodiments of the present application. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0152] Those skilled in the art will appreciate that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

[0153] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0154] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0155] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but the scope of the rights of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present invention should be within the scope of the rights of the present invention.

Claims

1. A static error calibration system for a current-steering digital-to-analog converter, characterized in that: The calibration system includes a current-steering digital-to-analog converter module, a measurement system, and a control system; Wherein, the current-steering digital-to-analog converter module includes a plurality of current-steering digital-to-analog converter units, and each of the current-steering digital-to-analog converter units includes a plurality of compensation digital-to-analog converter units; The current steering type digital-to-analog converter unit includes a resistor ladder, a first switch tube, a cascode tube and a first current source tube; the resistor ladder is provided with a first differential output terminal and a second differential output terminal, and the first switch tube is provided with a first differential input terminal and a second differential input terminal; the first switch tube and the cascode tube are connected to the resistor ladder and the first current source tube respectively; the first current source tube is also connected to a reference ground; The compensation digital-to-analog converter unit includes a second switch tube and a second current source tube; the second switch tube is respectively provided with an input end and an output end of the compensation digital-to-analog converter unit, the second switch tube is connected to the second current source tube, and the second current source tube is also connected to a reference ground; The output ends of the plurality of compensation digital-to-analog converter units are connected to the common connection end of the first switch tube and the common-source common-gate tube and the first current source tube; The measurement system is used to measure the output current or load voltage of the current-steering digital-to-analog converter module; The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage and the control signal measured by the measurement system.

2. The static error calibration system of a current-steering digital-to-analog converter according to claim 1, characterized in that: One of the current steering type digital-to-analog converter units includes one of the compensation digital-to-analog converter units or a plurality of the compensation digital-to-analog converter units; Wherein, when one of the current steering type digital-to-analog converter units includes one of the compensation digital-to-analog converter units, the output end of the compensation digital-to-analog converter unit is connected to the first switch tube and the common connection end of the common source tube and the first current source tube; When one of the current-steering digital-to-analog converter units includes a plurality of the compensation digital-to-analog converter units, the output end of each of the compensation digital-to-analog converter units is connected to the first switch tube and the common connection end of the common-source common-gate tube and the first current source tube.

3. The static error calibration system of a current-steering digital-to-analog converter according to claim 2, characterized in that: When one current steering type digital-to-analog converter unit includes a plurality of compensation digital-to-analog converter units, each of the compensation digital-to-analog converter units includes one second switch tube, and each of the compensation digital-to-analog converter units includes two i the second current source tube; Wherein, i is an integer ranging from 0 to n, and n represents the total number of the compensation digital-to-analog converter units, and the number of the second current source tubes in each of the compensation digital-to-analog converter units is different.

4. The static error calibration system of a current-steering digital-to-analog converter according to claim 1, characterized in that: The compensation digital-to-analog converter unit includes a single-ended output type or a differential output type; When the compensation digital-to-analog converter unit adopts the single-ended output type, the single-ended output end of the second switch tube in a plurality of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube; the second switch tubes in a plurality of the compensation digital-to-analog converter units are respectively provided with single-ended input ends; When the compensation digital-to-analog converter unit adopts the differential output type, the first differential output end of the second switch tube in several of the compensation digital-to-analog converter units is connected to the common connection end of the first switch tube and the common source and common gate tube and the first current source tube, and the second differential output ends of the second switch tube in several of the compensation digital-to-analog converter units are respectively connected to the power supply; the second switch tubes in several of the compensation digital-to-analog converter units are respectively provided with a first differential input end and a second differential input end.

5. The static error calibration system of a current-steering digital-to-analog converter according to claim 1, characterized in that: The measurement system uses a transimpedance amplifier; The transimpedance amplifier is used to measure the output current of the current-steering digital-to-analog converter module, and then output a voltage corresponding to the output current.

6. The static error calibration system of a current-steering digital-to-analog converter according to claim 1, characterized in that: The measurement system and the control system are integrated inside the current-steering digital-to-analog converter module; Alternatively, the measurement system and the control system are arranged outside the current-steering digital-to-analog converter module.

7. A static error calibration system for a current-steering digital-to-analog converter according to any one of claims 1 to 6, characterized in that: The calibration system also includes a host computer; The host computer is used to output the control signal; The control system is used to calibrate the current-steering digital-to-analog converter module according to the output current or the load voltage measured by the measurement system and the control signal output by the host computer.

8. A static error calibration method for a current-steering digital-to-analog converter, characterized in that: The calibration method is applied to a static error calibration system of a current-steering digital-to-analog converter according to any one of claims 1 to 7, and the calibration method comprises the following steps: Performing gain calibration on the current-steering digital-to-analog converter module so that the compensation current does not exceed the coverage range of the compensation digital-to-analog converter unit in the current-steering digital-to-analog converter module; Perform nonlinear calibration on the current-steering DAC module to reduce differential nonlinearity and integral nonlinearity; The step of performing gain calibration on the current-steering digital-to-analog converter module is performed again to reduce the gain error introduced by the nonlinear calibration.

9. The static error calibration method of a current-steering digital-to-analog converter according to claim 8, characterized in that: The gain calibration of the current steering type digital-to-analog converter module comprises the following steps: Turning off all the compensation DAC units in the current-steering DAC module; placing the compensation digital-to-analog converter unit of the reference current source at an intermediate codeword; Measuring a first output full-scale current of the current-steering digital-to-analog converter module; increasing or decreasing an input bit of the compensation digital-to-analog converter unit to adjust an output of the compensation digital-to-analog converter unit; Measuring a second output full-scale current of the current-steering digital-to-analog converter module; Calculating a gain error based on the first output full-scale current and the second output full-scale current; If the gain error becomes smaller, return to the step of increasing or decreasing the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit until the gain error reaches a minimum value, decrease or increase the input bit of the compensation digital-to-analog converter unit to adjust the output of the compensation digital-to-analog converter unit, and then end the calibration; If the gain error increases or remains unchanged, the input bit of the compensation DAC unit is reduced or increased to adjust the output of the compensation DAC unit until the gain error reaches a minimum value, and then the calibration is terminated.

10. The static error calibration method of a current-steering digital-to-analog converter according to claim 8, characterized in that: The nonlinear calibration of the current steering type digital-to-analog converter module comprises the following steps: Calculate the equivalent current of each current-steering digital-to-analog converter unit in the current-steering digital-to-analog converter module; wherein each equivalent current includes the output current of the corresponding current-steering digital-to-analog converter unit when the thermometer code is controlled and the output current of the corresponding current-steering digital-to-analog converter unit when the binary code is controlled; Determine the maximum value among the equivalent currents as the standard current value; The compensation DAC unit of the thermometer code is adjusted so that the output current of the current steering DAC unit is consistent with NI STD The difference between them is minimized; where N is a positive integer, I STD Indicates the standard current value; The compensation digital-to-analog converter unit of the binary code is adjusted so that the output current of the current-steering digital-to-analog converter unit is The difference between them is minimized; where M is a positive integer.

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