CN107037760A - A kind of input current type artifical resistance device and resistance control method - Google Patents

本发明的目的在于提供一种输入电流型模拟电阻器及电阻控制方法，其包括依次串联连接的电流源、电流‑电压转换器、AD转换器、处理器、DA转换器和电压‑电压转换器，在模拟电阻的过程中，以上各电路中会引起误差的主要是电流‑电压转换器、AD转换器、DA转换器和电压‑电压转换器，通过最终模拟电阻的误差分析并通过在嵌入式处理器中对误差进行消除并结合校准拟合实现对其误差进行消除，从而提高最终输出模拟电阻精度和阻值稳定度。

The object of the present invention is to provide a kind of input current type analog resistor and resistance control method, it comprises the current source, current-voltage converter, AD converter, processor, DA converter and voltage-voltage converter connected in series successively , in the process of simulating resistors, the above circuits will mainly cause errors from current-voltage converters, AD converters, DA converters, and voltage-voltage converters. Through the error analysis of the final analog resistors and through the embedded The error is eliminated in the processor and combined with the calibration fitting to eliminate the error, thereby improving the accuracy and stability of the final output analog resistance.

一种输入电流型模拟电阻器及电阻控制方法An input current type analog resistor and resistance control method

技术领域technical field

本发明涉及伺服电气元件领域，具体的涉及一种输入电流型模拟电阻器。The invention relates to the field of servo electrical components, in particular to an input current type analog resistor.

背景技术Background technique

现有的可变电阻器有电阻箱、机械电位器、数字电位器这些传统电阻箱均为手动可变电阻值，很难自动调节。为了可以程控调节，也出现了一些程控模拟电阻，最常用方式为数字合成技术，(通过给定的输入激励电流)，调节输出电压以实现合成电阻阻值的控制。其中输出电压等于激励电流乘以合成电阻，即输出电压与激励电流成正比，与设置的合成电阻成正比，具体如图1所示，通过电流测量部件测量激励电流I_i的大小，再根据合成电阻设置值R_x，设置程控电压源输出的直流电压U_o，其中U_o＝I_i×R_x。The existing variable resistors include resistance boxes, mechanical potentiometers, and digital potentiometers. These traditional resistance boxes are all manually variable resistance values, which are difficult to automatically adjust. In order to be able to be adjusted by program control, some program-controlled analog resistors have also appeared. The most commonly used method is digital synthesis technology (through a given input excitation current), and the output voltage is adjusted to control the resistance value of the synthesized resistor. The output voltage is equal to the excitation current multiplied by the synthesis resistance, that is, the output voltage is proportional to the _excitation current and the set synthesis resistance, as shown in Fig. The resistance setting value R _x sets the DC voltage U _o output by the programmable voltage source, where U _o =I _i ×R _x .

该程控方案的核心原理是通过将固定输入电流转变为电压后送入到DAC的参考端，作为输出DAC的参考电压，该方案的不足在于通过调节DAC的参考电压，使得DAC本身在不同的电阻值下产生的误差存在非线性，通过修正很难解决由此引入的误差，导致最终得到的模拟电阻的稳定性不太理想。The core principle of this program control scheme is to convert the fixed input current into a voltage and then send it to the reference terminal of the DAC as the reference voltage of the output DAC. The error generated under the value is non-linear, and it is difficult to solve the error introduced by correction, which leads to the unsatisfactory stability of the final analog resistance.

因为任何DAC和ADC的精度严重依赖于基准的性能。如果将输入作为DAC参考基准使得整个输出DAC的精度得不到保证。Because the accuracy of any DAC and ADC is heavily dependent on the performance of the reference. If the input is used as a DAC reference, the accuracy of the entire output DAC cannot be guaranteed.

发明内容Contents of the invention

基于以上方法中存在的问题，本发明的技术方案通过ADC采集前端固定输入电流，根据电阻设置值，输出端通过DAC给出相应电压值，达到模拟电阻目的，通过选择合适参考电压使前端ADC和后端DAC均工作在最佳状态，从而规避了去调节ADC和DAC参考电压引起的非线性误差，虽然前端又引入了一个ADC，通过合理的设计，前端ADC引入的误差为线性误差，比较容易进行修正从而达到输出模拟电阻稳定的目的。此外，还可再结合误差产生的原因，进行针对性的分析和去除，减小拟合的难度和工作量。Based on the problems in the above method, the technical solution of the present invention collects the front-end fixed input current through the ADC, and according to the resistance setting value, the output terminal provides the corresponding voltage value through the DAC to achieve the purpose of simulating the resistance. By selecting a suitable reference voltage, the front-end ADC and The back-end DACs all work in the best state, thereby avoiding the nonlinear error caused by adjusting the reference voltage of the ADC and DAC. Although the front-end introduces an ADC, through a reasonable design, the error introduced by the front-end ADC is a linear error, which is relatively easy Make corrections to achieve the purpose of stabilizing the output analog resistance. In addition, combined with the cause of the error, targeted analysis and elimination can be carried out to reduce the difficulty and workload of fitting.

并且由于数字域里实现比模拟域里更高精度、更高可靠和更低价格的各种信号处理功能，数字抑制噪声的能力远大于模拟信号，在模拟信号的存储和传输过程中，噪声和失真会被累积，从而对信号的处理产生不良的效果，而在数字域里，数字信号可以无损地存储和传输，这也是本发明技术方案的另一优势。And because various signal processing functions with higher precision, higher reliability and lower price are realized in the digital domain than in the analog domain, the ability of digital to suppress noise is much greater than that of analog signals. During the storage and transmission of analog signals, noise and Distortion will be accumulated, which will have adverse effects on signal processing. In the digital domain, digital signals can be stored and transmitted without loss, which is another advantage of the technical solution of the present invention.

具体为一种输入电流型模拟电阻器，其特征在于：包括依次串联连接的电流源、电流-电压转换器、AD转换器、处理器、DA转换器和电压-电压转换器，其中处理器接收AD转换器输入的电压值，再根据目标电阻阻值控制DA转换器的输出，使其输出相应的电压信号通过电压-电压转换器控制生成所需要的电压。Specifically, it is an input current type analog resistor, which is characterized in that it includes a current source, a current-voltage converter, an AD converter, a processor, a DA converter and a voltage-voltage converter connected in series in sequence, wherein the processor receives The voltage value input by the AD converter, and then control the output of the DA converter according to the target resistance value, so that the output corresponding voltage signal is controlled by the voltage-voltage converter to generate the required voltage.

进一步地，其特征在于：所述电流-电压转换器包括一运算放大器，其正向输入端连接有电流源，同时还连接有高精度固定值电阻R_ref，反向输入端连接至与输出端连接的串联采样电阻R1与R2之间的连接点。Further, it is characterized in that: the current-voltage converter includes an operational amplifier, the positive input end of which is connected to a current source, and is also connected to a high-precision fixed-value resistor R _ref , and the reverse input end is connected to the output end Connect the connection point between the series sense resistors R1 and R2.

进一步地，其特征在于：对于模拟电阻值的修正按照如下计算方式进行：其中R_x为所需模拟的电阻器阻值，其中U_a表示输入端电压值，U_b表示输出端电压值，输入电流为I_i，R_ref为电流-电压转换器中运算放大器正向输入端所连接的取样电阻阻值。Further, it is characterized in that: the correction of the analog resistance value is performed according to the following calculation method: Where R _x is the resistance value of the resistor to be simulated, where U _a represents the voltage value of the input terminal, U _b represents the voltage value of the output terminal, the input current is I _i , and R _ref is the positive input of the operational amplifier in the current-voltage converter The resistance value of the sampling resistor connected to the terminal.

进一步地，其特征在于：对于模拟电阻值的修正，在考虑所述运算放大器的失调电流和失调电压的情况下，运算放大器的实际输出电压与理想输出电压的误差为：Further, it is characterized in that: for the correction of the analog resistance value, in consideration of the offset current and offset voltage of the operational amplifier, the error between the actual output voltage of the operational amplifier and the ideal output voltage is:

其中，U_IO为所述运算放大器的失调电压，失调电流为I_B1和I_B2为所述运算放大器正向、负向输入端的失调电流， _Wherein , U 10 is the offset voltage of the operational amplifier, and the offset current is that I _B1 and I _B2 are the offset currents of the forward and negative input terminals of the operational amplifier,

在处理器汇总将其误差予以补偿。The errors are compensated in the processor summary.

进一步地，其特征在于：对于模拟电阻值的修正，还要考虑所述第一运算放大器的温度漂移的情况下，第一运算放大器的的误差，并将其误差在处理器中补偿，该误差计算公式为：Further, it is characterized in that: for the correction of the analog resistance value, the error of the first operational amplifier is also considered in the case of the temperature drift of the first operational amplifier, and its error is compensated in the processor, the error The calculation formula is:

输入失调电流I_B1、I_B2的温度漂移分别为TCI_B1和TCI_B2，输入失调电压U_IO温度漂移为TCV。The temperature drifts of the input offset currents I _B1 and I _B2 are respectively TCI _B1 and TCI _B2 , and the temperature drift of the input offset voltage U _IO is TCV.

进一步地，其特征在于：Further, it is characterized in that:

还要考虑AD转换器和DA转换器的转换误差，其公式分别为：Also consider the conversion errors of the AD converter and the DA converter, and their formulas are:

ΔU_ADC＝N_ADCU_LSBADC；ΔU _ADC = N _ADC U _LSBADC ;

ΔU_DAC＝N_DACU_LSBDAC；ΔU _DAC = N _DAC U _LSBDAC ;

其中，U_LSBADC、U_LSBDAC分别指ADC、DAC输入数字量最低位为1，其余为0时对应的转换电压，即Among them, U _LSBADC and U _LSBDAC respectively refer to the corresponding conversion voltage when the lowest bit of the input digital quantity of ADC and DAC is 1, and the rest are 0, namely

其中n1，n2分别表示ADC、DAC转换数据最大位数 Among them, n1 and n2 respectively represent the maximum number of digits of ADC and DAC conversion data

N_ADC根据实测ADC误差确定,N_DAC根据实测DAC误差确定。N _ADC is determined according to the measured ADC error, and N _DAC is determined according to the measured DAC error.

进一步地，其特征在于：所述电阻模拟器的还要考虑第二运算放大器失调电流与失调电压导致的误差，其计算方式如下： Further, it is characterized in that: the resistance simulator also considers the error caused by the offset current and offset voltage of the second operational amplifier, and its calculation method is as follows:

其中，R₁’为输出部分运算放大器的负向输入端与地之间的采样电阻Among them, R ₁ ' is the sampling resistance between the negative input terminal of the output part of the operational amplifier and the ground

R₂’为输出部分运算放大器的正向输入端所连接的输入电阻R ₂ 'is the input resistance connected to the positive input of the output part of the operational amplifier

R_f’为输出部分运算放大器的正向输入端与输出端之间的采样电阻R _f ' is the sampling resistance between the positive input terminal and the output terminal of the output part of the operational amplifier

U_IO’为输出部分运算放大器的失调电压U _IO ' is the offset voltage of the output section op amp

I_B1’为输出部分运算放大器正向输入端的失调电流I _B1 'is the offset current at the positive input of the operational amplifier of the output section

I_B2’为输出部分运算放大器负向输入端的失调电流I _B2 'is the offset current of the negative input terminal of the output part of the operational amplifier

进一步地，其特征在于：所述电阻模拟器还要考虑输出驱动部分的第二运算放大器温度漂移产生的误差Further, it is characterized in that: the resistance simulator also considers the error caused by the temperature drift of the second operational amplifier of the output drive part

其中，TCV’为输出部分运算放大器的失调电压温度漂移Among them, TCV' is the offset voltage temperature drift of the output part of the operational amplifier

TCI_B1’为输出部分运算放大器正向输入端的失调电流温度漂移TCI _B1' is the offset current temperature drift of the positive input of the output part of the operational amplifier

TCI_B2’为输出部分运算放大器负向输入端的失调电流温度漂移TCI _B2' is the offset current temperature drift of the negative input of the output part of the operational amplifier

T为温度漂移量T is the temperature drift

进一步地，其特征在于：模拟电阻值的计算公式如下：Further, it is characterized in that: the formula for calculating the analog resistance value is as follows:

其中，电流-电压变换比率为K₁，电压-电压变换比率为K₂。Wherein, the current-voltage conversion ratio is K ₁ , and the voltage-voltage conversion ratio is K ₂ .

本发明还提供一种输入电流型模拟电阻器的电阻控制方法，其特征在于：采用上述任一方案所述的电压型模拟电阻器，对其电阻控制采用拟合和误差消除结合的方法进行。The present invention also provides a resistance control method of an input current-type analog resistor, which is characterized in that: the voltage-type analog resistor described in any of the above schemes is used, and the resistance control is carried out by combining fitting and error elimination.

附图说明Description of drawings

图1现有技术中模拟电阻器原理图Fig. 1 schematic diagram of analog resistor in the prior art

图2本发明的输入电流型模拟电阻器的原理框图The functional block diagram of the input current type analog resistor of Fig. 2 of the present invention

图3(a)本发明的输入电流型模拟电阻器的电路结构图The circuit structure diagram of the input current type analog resistor of Fig. 3 (a) the present invention

图3(b)本发明的输入电流型模拟电阻器的等效电路图The equivalent circuit diagram of the input current type analog resistor of Fig. 3 (b) the present invention

图4电流-电压转换部分的误差分析模型Figure 4 The error analysis model of the current-voltage conversion part

图5电压-电压转换器部分的误差分析模型Figure 5 The error analysis model of the voltage-to-voltage converter part

具体实施方式detailed description

结合具体实施例对本发明进行具体说明如下：The present invention is specifically described as follows in conjunction with specific embodiments:

本发明的框图如图2所示，首先，电流电压转换器采集输入电流I_i并将其转换为电压信号，使之满足AD转换器的输入要求；高精度AD转换器采集该电压并输入到嵌入式处理器中，嵌入式处理器对电压使用滤波、误差校正等算法进行处理，再根据所设定的目标合成电阻阻值R_x控制DA转换器的输出，使其输出相应的电压信号，同时通过输出设备显示电压、电流和电阻值；最后，电压-电压转换器将DA转换器输出的电压转换为电压输出U_b。The block diagram of the present invention is as shown in Figure 2, at first, the current-voltage converter collects input current I _i and converts it into a voltage signal, so that it meets the input requirements of the AD converter; the high-precision AD converter collects the voltage and inputs it to In the embedded processor, the embedded processor uses algorithms such as filtering and error correction to process the voltage, and then controls the output of the DA converter according to the set target synthetic resistance value _Rx , so that it outputs the corresponding voltage signal. At the same time, the voltage, current and resistance value are displayed through the output device; finally, the voltage-voltage converter converts the voltage output by the DA converter into a voltage output U _b .

对于本发明的电流激励电路模拟电阻值的电路中，电流电压变换器中的电流-电压变换比率为K₁，前端ADC位数N₁，ADC的参考电压为U₁，嵌入式处理器读取的电流-电压变换后输出的电压经过AD转换器变换后的数值为D₁；后端DAC位数为N₂，DAC的参考电压为U₂，电压-电压转换器所需输出电压的对应数字值为D₂，电压-电压变换比率为K₂，计算模拟电阻R_x的方法如下：For the current excitation circuit of the present invention simulating the resistance value circuit, the current-voltage conversion ratio in the current-voltage converter is K ₁ , the number of digits of the front-end ADC is N ₁ , the reference voltage of the ADC is U ₁ , and the embedded processor reads The value of the output voltage after the current-voltage conversion of the current-voltage conversion of the AD converter is D ₁ ; the number of digits of the back-end DAC is N ₂ , the reference voltage of the DAC is U ₂ , and the corresponding number of the output voltage required by the voltage-voltage converter The value is D ₂ , the voltage-voltage conversion ratio is K ₂ , and the method of calculating the analog resistance R _x is as follows:

即根据前端ADC获取的数字值D₁和处理器输出给后端DAC的数字值D₂以及输入的电流值I_i来计算模拟电阻值。图5为本发明技术方案中嵌入式处理器连接的输出电压驱动电路，其包含了DAC和电压-电压转换器，输出电压驱动电路最终输出的电压为U_b，输出电流为I_i，通过前端ADC采集后，后端通过设置电阻值，采用嵌入式处理器控制输出DAC数字信号值D₂，通过输出缓冲驱动电路，从而实现模拟电阻。That is, the analog resistance value is calculated according to the digital value D ₁ obtained by the front-end ADC, the digital value D ₂ output by the processor to the back-end DAC, and the input current value I _i . Fig. 5 is the output voltage driving circuit connected to the embedded processor in the technical solution of the present invention, which includes a DAC and a voltage-voltage converter, the final output voltage of the output voltage driving circuit is U _b , and the output current is I _i , through the front end After the ADC is collected, the back-end sets the resistance value, uses the embedded processor to control the output DAC digital signal value D ₂ , and drives the circuit through the output buffer to realize the analog resistance.

通过进一步对电路误差分析，主要包括输入电流-电压转换电路失调电压和失调电流以及温度漂移的影响，ADC和DAC转换误差的影响，输出电压-电压转换电路失调电压和失调电流以及温度漂移的影响。以上误差主要为线性误差，可以考虑通过最终的校准拟合来消除。具体方法为，处理器接收AD转换器输入的电压值，再根据目标电阻阻值控制DA转换器的输出,使其输出相应的电压信号控制生成所需要的电压。通过多次输入及多次输出值调整，来对调整值进行拟合(例如采用最小二乘法)，最终确定调整公式。Through further analysis of circuit errors, it mainly includes the influence of input current-voltage conversion circuit offset voltage and offset current and temperature drift, the influence of ADC and DAC conversion errors, the output voltage-voltage conversion circuit offset voltage and offset current and the influence of temperature drift . The above errors are mainly linear errors, which can be considered to be eliminated by the final calibration fitting. The specific method is that the processor receives the voltage value input by the AD converter, and then controls the output of the DA converter according to the target resistance value, so that it outputs a corresponding voltage signal to control and generate the required voltage. The adjustment value is fitted (for example, using the least square method) through multiple input and multiple output value adjustments, and the adjustment formula is finally determined.

不过，即使为线性误差，但是由于误差的原因较多，其整合的误差曲线也非常复杂，要想准确拟合，数据量需要很大，鉴于此，本发明还提供一种误差原因分析及去除与拟合相结合的方式来实现精确电阻值的方法。However, even if it is a linear error, since there are many reasons for the error, the integrated error curve is also very complicated. To accurately fit, the amount of data needs to be large. In view of this, the present invention also provides an error cause analysis and removal method. A method combined with fitting to achieve precise resistance values.

其中，输入端包括一个取样电阻法电流测量电路的误差，建立误差分析模型如图4所示，设两个输入端失调电流为I_B1和I_B2，所谓失调电流是指运算放大器的两端在理想状态为“虚断”，但在实际电路中，运算放大器的正负输入端均有少量电流流入，此电流就是失调电流，输入失调电压为U_IO，此处所谓的失调电压是指在理想状态下，运算放大器的正负输入端的电压是相同时，输出电压就等于0，但是实际中，运算放大器必须在一个输入端额外施加一个小电压才能使输出电压等于0V，该微小电压即为失调电压，需要指出的是，失调电流和失调电压都可以通过预先测量获得，所以，在使用前通过对ADC阶段的运算放大器输入失调电流和输入失调电压的预先测定，可以获得I_B1、I_B2以及U_IO，从图4可以看出，设运放输入端电压分别为U₊和U_-，流过电阻R₁和R₂的电流分别为I₁和I₂。通过分析可以得到以下方程式：Among them, the input terminal includes the error of a sampling resistance current measurement circuit. The error analysis model is established as shown in Figure 4. The offset currents of the two input terminals are I _B1 and I _B2 . The so-called offset current refers to the two ends of the operational amplifier. The ideal state is "virtual break", but in the actual circuit, a small amount of current flows into the positive and negative input terminals of the operational amplifier. This current is the offset current, and the input offset voltage is U _IO . The so-called offset voltage here refers to the ideal Under normal conditions, when the voltages of the positive and negative input terminals of the operational amplifier are the same, the output voltage is equal to 0, but in practice, the operational amplifier must apply an additional small voltage to one input terminal to make the output voltage equal to 0V, and this small voltage is the offset. voltage, it should be pointed out that both the offset current and the offset voltage can be obtained by pre-measurement, so, by pre-measurement of the input offset current and input offset voltage of the operational amplifier in the ADC stage before use, I _B1 , I _B2 and U _IO , as can be seen from Figure 4, assume that the voltages at the input terminals of the operational amplifier are U ₊ and U _- respectively, and the currents flowing through resistors R ₁ and R ₂ are I ₁ and I ₂ respectively. The following equation can be obtained by analysis:

U₊＝(I_i-I_B1)·R_ref+U_IO U ₊ ＝(I _i -I _B1 )·R _ref +U _IO

U_-＝I₁R₁ U _- ＝I ₁ R ₁

I₂＝I₁+I_B2 I ₂ =I ₁ +I _B2

U₊＝U_- U _{+ ＝} U-

由上式可以得到can be obtained from the above formula

其中U₊为电流-电压转换部分的第一运算放大器正输入端处的电压值，U_-为电流-电压转换部分的第一运算放大器负输入端处的电压值，输入电流型模拟电阻器的输入电流为I_i，电阻R₁为电流-电压转换部分的第一运算放大器的反向输入端与地之间的采样电阻，电阻R₂为电流-电压转换部分的第一运算放大器的反向输入端与输出端之间的采样电阻，电阻R_ref为电流-电压转换部分的第一运算放大器的正向输入端所连接的高精度固定值电阻，电压U_o’为电流-电压转换部分的第一运算放大器的输出端电压。Wherein U ₊ is the voltage value at the positive input terminal of the first operational amplifier of the current _- voltage conversion part, U- is the voltage value at the negative input terminal of the first operational amplifier of the current-voltage conversion part, and the input current-type analog resistor The input current is I _i , the resistor R1 is the sampling resistor between the inverting input terminal of the _first operational amplifier of the current _- voltage conversion part and the ground, and the resistor R2 is the inverse of the first operational amplifier of the current-voltage conversion part The sampling resistor between the input terminal and the output terminal, the resistance R _ref is a high-precision fixed-value resistor connected to the positive input terminal of the first operational amplifier of the current-voltage conversion part, and the voltage U _o ' is the current-voltage conversion part The output voltage of the first operational amplifier.

而如果将电流-电压转换部分的第一运算放大器当做理想的运算放大器来处理，不考虑失调电压和失调电流的情况，则此时运第一算放大器的输出电压值为为理想情况下的输出电压值。And if the first operational amplifier in the current-voltage conversion part is treated as an ideal operational amplifier, regardless of the offset voltage and offset current, the output voltage of the first operational amplifier at this time is is the ideal output voltage value.

那么，有运算放大器失调电压和失调电流的存在，导致电流-电压转换部分的第一运算放大器的实际输出电压与理想输出电压的误差为Then, due to the existence of the offset voltage and offset current of the operational amplifier, the error between the actual output voltage and the ideal output voltage of the first operational amplifier of the current-voltage conversion part is

通过在嵌入式处理器中对该误差进行修正可得到对输入电流-电压转换电路修正过得模拟电阻值。By correcting the error in the embedded processor, the analog resistance value corrected for the input current-voltage conversion circuit can be obtained.

同时，在上述误差修正的基础上，进一步考虑温度漂移对输入电流型模拟电阻器带来的影响。At the same time, on the basis of the above-mentioned error correction, the influence of temperature drift on the input current-type analog resistor is further considered.

设输入失调电流I_B1、I_B2的温度漂移分别为TCI_B1和TCI_B2，输入失调电压U_IO温度漂移为TCV，可以得到由于温度漂移带来的误差方程式为Let the temperature drift of the input offset current I _B1 and I _B2 be TCI _B1 and TCI _B2 respectively, and the temperature drift of the input offset voltage U _IO be TCV, and the error equation caused by the temperature drift can be obtained as

U₊＝(I_i-TCI_B1ΔT)·R_ref+TCVΔTU ₊ ＝(I _i -TCI _B1 ΔT)·R _ref +TCVΔT

U_-＝I₁R₁ U _- ＝I ₁ R ₁

I₂＝I₁+TCI_B2ΔTI ₂ =I ₁ +TCI _B2 ΔT

U₊＝U_- U _{+ ＝} U-

由此可以计算得到在具有温度漂移的情况下，ADC阶段的运算放大器的输出电压为： From this, it can be calculated that in the case of temperature drift, the output voltage of the operational amplifier in the ADC stage is:

理想情况下电流-电压转换部分的第一运算放大器的输出电压值为：Ideally, the output voltage value of the first operational amplifier in the current-voltage conversion section is:

所以，在具有失调电压和失调电流的情况下，由于温度漂移导致ADC阶段运算放大器的实际输出电压与理想输出电压之间的误差为：So, with offset voltage and offset current, the error between the actual and ideal output voltage of the operational amplifier in the ADC stage due to temperature drift is:

实际ADC采集到的电压为The voltage collected by the actual ADC is

通过在嵌入式处理器中对实际测得U_o’进行修正，从而提高输出模拟电阻精度。By correcting the actually measured U _o ' in the embedded processor, the accuracy of the output analog resistance is improved.

接下来，对AD转换器和DA转换误差进行分析Next, analyze the AD converter and DA conversion error

实际上AD转换器和DA转换器都存在转换误差，分为静态误差和动态误差。产生静态误差的原因有，基准源的不稳定，运放的零点漂移，模拟开关导通时的内阻和压降以及电阻网络中阻值的偏差等。动态误差则是在转换的动态过程中产生的附加误差，它是由于电路中分布参数的影响，使各位的电压信号到达解码网络输出端的时间不同所致。通常转换误差用最小输出电压U_LSB的倍数表示，即In fact, both the AD converter and the DA converter have conversion errors, which are divided into static errors and dynamic errors. The reasons for the static error include the instability of the reference source, the zero drift of the operational amplifier, the internal resistance and voltage drop when the analog switch is turned on, and the deviation of the resistance value in the resistor network. The dynamic error is an additional error generated during the dynamic process of conversion. It is caused by the influence of the distribution parameters in the circuit, so that the time for each voltage signal to reach the output of the decoding network is different. Usually the conversion error is expressed in multiples of the minimum output voltage U _LSB , i.e.

ΔU_o＝NU_LSB ΔU _o =NU _LSB

其中，U_LSB指ADC和DAC数字量最低位为1，其余为0时对应的转换电压值，即Among them, U _LSB refers to the corresponding conversion voltage value when the lowest bit of the ADC and DAC digital quantity is 1, and the rest are 0, that is

其中n为ADC或者DAC的最大转换位数； Where n is the maximum conversion number of ADC or DAC;

通过ADC误差分析后，进入嵌入式处理器后，实际修正后的电压值U_a’为After analyzing the ADC error and entering the embedded processor, the actual corrected voltage value U _a ' is

其中，D₁为嵌入式处理器读取的ADC阶段运算放大器进行电流-电压变换后输出的电压经过AD转换器变换后的数值，N₁为AD转换器位数，U₁为AD转换器的参考电压。Among them, D ₁ is the value of the output voltage after the current-voltage conversion of the operational amplifier in the ADC stage read by the embedded processor after being converted by the AD converter, N ₁ is the number of bits of the AD converter, and U ₁ is the value of the AD converter reference voltage.

ΔU_OP11-输入失调电流和失调电压导致的误差；ΔU _OP11 - error due to input offset current and offset voltage;

TC₁₁ΔT-输入部分温度漂移导致的误差；TC ₁₁ ΔT-The error caused by the temperature drift of the input part;

N_ADCU_LSBADC-AD转换器导致的转换误差；N _ADC U _LSBADC - conversion error caused by AD converter;

N_ADC根据实测ADC误差确定。N _ADC is determined from the measured ADC error.

进一步对输出部分DAC误差进行分析，分析原理以及误差产生的原因同上述ADC阶段的误差分析一致。Further analyze the DAC error of the output part, the analysis principle and the cause of the error are consistent with the error analysis of the above-mentioned ADC stage.

ΔU_DAC＝N_DACU_LSBDAC ΔU _DAC = N _DAC U _LSBDAC

进一步对输出电压-电压转换部分误差分析，该部分误差模型图如图5所示Further analyze the error of the output voltage-voltage conversion part, the error model diagram of this part is shown in Figure 5

可以得到电压-电压转换部分输出电压的误差为The error of the output voltage of the voltage-voltage conversion part can be obtained as

ΔU_OPP-输出部分电压-电压部分由于失调电流与失调电压导致的输出电压误差，上述公式中的I_B1’、I_B2’、U_IO’、R₁’、R₂’都是输出部分第二运算放大器处的参数，其含义与输入部分运算放大器出的参数对应，具体为。ΔU _OPP - output part voltage - the output voltage error caused by the offset current and offset voltage in the voltage part, I _B1 ', I _B2 ', U _IO ', R ₁ ', R ₂ ' in the above formula are the second part of the output part The meaning of the parameters at the operational amplifier corresponds to the parameters at the input part of the operational amplifier, specifically.

R₁’为输出部分运算放大器的负向输入端与地之间的采样电阻R ₁ 'is the sampling resistor between the negative input terminal of the output part of the operational amplifier and the ground

R₂’为输出部分运算放大器的正向输入端所连接的输入电阻R ₂ 'is the input resistance connected to the positive input of the output part of the operational amplifier

R_f’为输出部分运算放大器的正向输入端与输出端之间的采样电阻R _f ' is the sampling resistance between the positive input terminal and the output terminal of the output part of the operational amplifier

U_IO’为输出部分运算放大器的失调电压U _IO ' is the offset voltage of the output section op amp

I_B1’为输出部分运算放大器正向输入端的失调电流I _B1 'is the offset current at the positive input of the operational amplifier of the output section

I_B2’为输出部分运算放大器负向输入端的失调电流I _B2 'is the offset current of the negative input terminal of the output part of the operational amplifier

温度漂移产生的误差表达式为The error expression caused by temperature drift is

TC_PΔT-输出部分电压-电压转换部分温度漂移带来的输出电压误差，上式中的各参数的含义是与输入部分对应参数在输出部分的类似表达。TC _P ΔT- output part voltage - the output voltage error caused by the temperature drift of the voltage conversion part. The meaning of each parameter in the above formula is a similar expression to the corresponding parameter of the input part in the output part.

从而可以得到输出电压进行误差修正后的表达式Thus, the expression of the output voltage after error correction can be obtained

D₂为DAC阶段电压-电压转换器所需输出电压的对应数字值，N₂为DA转换器位数，U₂为DA转换器的参考电压。D ₂ is the corresponding digital value of the output voltage required by the voltage-to-voltage converter in the DAC stage, N ₂ is the number of digits of the DA converter, and U ₂ is the reference voltage of the DA converter.

进一步对最终模拟电阻经过误差修正后的表达式：Further, the error-corrected expression of the final analog resistance is:

其中，电流-电压变换比率为K₁，电压-电压变换比率为K₂。Wherein, the current-voltage conversion ratio is K ₁ , and the voltage-voltage conversion ratio is K ₂ .

尽管已描述了本发明的优选实施例，但本领域内的技术人员一旦得知了基本创造性概念，则可对这些实施例作出另外的变更和修改。所以，所附权利要求意欲解释为包括优选实施例以及落入本发明范围的所有变更和修改。While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

显然，本领域的技术人员可以对本发明进行各种改动和变型而不脱离本发明的精神和范围。这样，倘若本发明的这些修改和变型属于本发明权利要求及其等同技术的范围之内，则本发明也意图包含这些改动和变型在内。Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.