CN115309222B - Precision current source device based on digital regulation and control slope compensation - Google Patents

Abstract

The invention discloses a precision current source device based on digital control slope compensation. In the present invention, the microcontroller and the voltage-type digital-to-analog converter are connected through a digital bus, the microcontroller and the numerically controlled slope voltage generator are connected through a digital bus, and the voltage-type digital-to-analog converter and the two numerically controlled slope voltage generators are respectively connected with the proportional The three input terminals of the summing amplifier are connected, and the output terminal of the proportional summing amplifier is connected to the input terminal of the voltage-controlled current source. Wherein, the two digitally controlled ramp voltage generators with the same topological structure both include a digitally controlled current source, a charging capacitor, a first analog switch, a voltage buffer, a second analog switch, and a third analog switch. The present invention only needs to output a control signal once for each compensation, so on the basis of ensuring fine adjustment, high precision and high smoothness, it further increases the bandwidth range of the current signal that can be generated.

Description

A precision current source device based on digital control slope compensation

Technical field

The invention belongs to the field of precision measuring instruments, and in particular relates to a precision current source device based on digital control slope compensation.

Background technique

Current sources are widely used in electronic instruments, especially playing an important role in high-precision current comparator bridge systems. In recent years, digital current source technology based on microcontrollers has developed rapidly. Most of the new generation of DC current comparator bridges and low-temperature current comparator bridges use digital current sources as the excitation sources for the bridge's master and slave circuits. The advantages of using a digital current source include: 1. The current can be quickly adjusted through software operation, and programming technology can be used to generate any current waveform, such as the slope commutation current waveform required for the operation of a low-temperature current comparator; 2. It is easy to access digital control system, thereby using software algorithms to achieve highly robust control effects.

A digital current source includes at least three main parts: a microcontroller, a digital-to-analog converter, and a voltage-controlled current source. Among them, the resolution of the digital-to-analog converter determines the resolution of the current output. The resolution of commercial high-precision digital-to-analog converters is usually within 20 bits (mostly 16 bits). In order to cope with high-resolution design requirements, technicians usually use two or more voltage-type digital-to-analog converters to add them according to different weight ratios to obtain a higher-resolution voltage output, and then convert the voltage into the required Other signal forms (such as current signals). In conventional applications, the digital-to-analog converters that are added and synthesized work synchronously, and the working logic is equivalent to a voltage-type digital-to-analog converter with higher bits. In some special application fields, such as the commutation current of low-temperature current comparators, the generated current signal is required to be finely adjustable, high-precision and high-smooth at the same time. Using the above technology can meet the first two requirements, but there are shortcomings in smoothness. The applicant previously proposed a precision digital voltage waveform compensation method to compensate for the main signal steps (including differential nonlinear errors) and solve the problem of signal smoothness. In the above solution, if a digital-to-analog converter is used as the compensation signal generator, concessions need to be made on the signal bandwidth. The reason is that the compensation signal generator must complete hundreds or even more refresh cycles within one refresh cycle of the main signal, thus limiting the refresh frequency of the main signal. Therefore, the above method has shortcomings in signal speed.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention proposes a precision current source device based on digital control slope compensation.

The invention includes a microcontroller, a voltage-type digital-to-analog converter, two numerically controlled slope voltage generators with the same topological structure, a proportional summing amplifier and a voltage-controlled current source.

The microcontroller and the voltage-type digital-to-analog converter are connected through a digital bus. The microcontroller is connected to the numerically controlled ramp voltage generator through a digital bus. The voltage-type digital-to-analog converter and the two numerically controlled ramps The voltage generator is respectively connected to the three input terminals of the proportional summing amplifier; the output terminal of the proportional summing amplifier is connected to the input terminal of the voltage-controlled current source; among them, a voltage type digital-to-analog converter and two digitally controlled slope voltage generators and a proportional adding amplifier constitute a voltage signal generating unit that can be digitally controlled and has slope compensation.

The digitally controlled ramp voltage generator is used to generate a signal in which the ramp waveform and the ground potential alternate with each other, and the signals generated by the two digitally controlled ramp voltage generators are opposite, including a digitally controlled current source, a charging capacitor, a first analog switch, a voltage buffer, and a third digitally controlled ramp voltage generator. The second analog switch and the third analog switch have the following specific structures:

The output terminal of the digitally controlled current source is connected to the first terminal of the charging capacitor, and charges are injected into the charging capacitor.

The second terminal of the charging capacitor is connected to the reference point to provide a reference potential for the charging voltage.

The input terminal of the first analog switch is connected to the first terminal of the charging capacitor, and the output terminal is connected to the reference point to provide a charge discharge path for the charging capacitor.

The input terminal of the voltage buffer is connected to the first terminal of the charging capacitor, and the charging voltage is buffered to the output terminal of the voltage buffer.

The input terminal of the second analog switch is connected to the output terminal of the voltage buffer, and the charging voltage is channeled to the output terminal of the digitally controlled ramp voltage generator in a time-sharing manner.

The input end of the third analog switch is connected to the reference point and conducts the reference potential to the output end of the digitally controlled slope voltage generator in a time-sharing manner.

The second analog switch and the third analog switch are analog switches with opposite control logics and are controlled by the same signal.

Beneficial effects of the present invention: The present invention only needs to output a control signal once for each compensation. Therefore, on the basis of ensuring fine adjustment, high precision and high smoothness, the bandwidth range of the current signal that can be generated is further improved.

Description of the drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing the exemplary embodiments of the present invention in more detail with reference to the accompanying drawings, wherein, in the exemplary embodiments of the present invention, the same reference numerals generally represent Same parts.

Figure 1 Principle block diagram of a precision current source device based on digital control slope compensation;

Figure 2 is a circuit diagram of the core part of a precision current source device based on digital control slope compensation;

Figure 3. Control timing of a precision current source device based on digital control slope compensation.

Detailed ways

Preferred embodiments of the invention will be described in more detail below. Although preferred embodiments of the present invention are described below, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein.

Figure 1 shows the schematic block diagram of a precision current source device based on digital control slope compensation.

It includes a microcontroller, a voltage-type digital-to-analog converter, two digitally controlled ramp voltage generators with the same topology, a proportional summing amplifier and a voltage-controlled current source.

The microcontroller and the voltage-type digital-to-analog converter are connected through a digital bus. The microcontroller is connected to the numerically controlled ramp voltage generator through a digital bus. The voltage-type digital-to-analog converter and the two numerically controlled ramps The voltage generator is respectively connected to the three input terminals of the proportional summing amplifier; the output terminal of the proportional summing amplifier is connected to the input terminal of the voltage-controlled current source; among them, a voltage type digital-to-analog converter and two digitally controlled slope voltage generators and a proportional adding amplifier constitute a voltage signal generating unit that can be digitally controlled and has slope compensation.

The digitally controlled ramp voltage generator is used to generate a signal in which the ramp waveform and the ground potential alternate with each other, and the signals generated by the two digitally controlled ramp voltage generators are opposite, including a digitally controlled current source, a charging capacitor, a first analog switch, a voltage buffer, and a third digitally controlled ramp voltage generator. The second analog switch and the third analog switch have the following specific structures:

The output end of the digitally controlled current source is connected to the first end of the charging capacitor to inject charge into the charging capacitor;

The second end of the charging capacitor is connected to the reference point to provide a reference potential for the charging voltage;

The input terminal of the first analog switch is connected to the first terminal of the charging capacitor, and the output terminal is connected to the reference point to provide a charge discharge path for the charging capacitor;

The input terminal of the voltage buffer is connected to the first terminal of the charging capacitor, and the charging voltage is buffered to the output terminal of the voltage buffer;

The input end of the second analog switch is connected to the output end of the voltage buffer, and the charging voltage is time-shared and channeled to the output end of the digitally controlled ramp voltage generator;

The input end of the third analog switch is connected to the reference point, and the reference potential is time-shared and conducted to the output end of the digitally controlled slope voltage generator;

The second analog switch and the third analog switch are analog switches with opposite control logics and are controlled by the same signal.

Furthermore, the digitally controlled current source is a multiplicative digital-to-analog converter.

Furthermore, the second analog switch and the third analog switch are single-pole single-throw analog switches.

Furthermore, the voltage buffer is a voltage follower composed of an operational amplifier.

Furthermore, the output end of the third analog switch is also equipped with a first-order RC filter circuit.

Example:

In order to facilitate understanding of the solutions and effects of the embodiments of the present invention, a specific application example is given below. Those skilled in the art will understand that this example is only to facilitate understanding of the present invention, and any specific details thereof are not intended to limit the present invention in any way.

In this embodiment, the precision current source device based on digital control slope compensation includes a microcontroller, a voltage-type digital-to-analog converter, two digitally controlled slope voltage generators with the same topology, a proportional summing amplifier, and a voltage-controlled current source. Among them, the microcontroller model is GD32F103, which is equipped with multi-channel SPI digital bus and digital IO for controlling digital-to-analog converters and analog switching devices. The voltage-controlled current source in the present invention can adopt voltage-controlled current source circuits with various topological principles. In this embodiment, an enhanced Howland voltage-controlled current source composed of dual operational amplifiers is used, which can generate the same voltage under the excitation of a voltage signal. The value is proportional to the current signal.

In the present invention, a voltage-type digital-to-analog converter, two numerically controlled slope voltage generators with the same topological structure, and a proportional summing amplifier constitute a digitally controllable voltage signal generating unit with slope compensation. Figure 2 shows the specific circuit form of the voltage-type digital-to-analog converter, the two-way digitally controlled ramp voltage generator with the same topology, and the proportional summing amplifier in this embodiment.

Among them, voltage-type analog-to-digital converters can choose various DAC devices such as multiplicative type, SAR type, sigma-delta type, etc. In this embodiment, the AD3552R multiplicative DAC is selected, and the AD8065 operational amplifier is used to form a peripheral circuit to implement IV conversion. That is, the device AD3552R and AD8065 together form the voltage-type digital-to-analog converter DAC _H. Its output voltage is shown in Figure 2 and Labeled V _H in Figure 3.

The topology of the two digitally controlled ramp voltage generators is the same. Taking the first digitally controlled ramp voltage generator as an example, it includes:

The multiplicative DAC device DAC _L1 , model AD3552R, can directly output current when no external circuit is installed. The current value is proportional to the code value sent by the digital bus, that is, it behaves as a digitally controlled current source. It should be noted that other types of DAC devices other than multiplicative types do not have this feature.

The capacitance value of charging capacitor C _L1 is selected as 1nF. One end of this capacitor is connected to DAC _L1 , and the other end is connected to the power reference ground so that the output current of DAC _L1 can charge it. The charging end of C _L1 is also connected to the input end of the first analog switch S1. The model of S1 is ADG1412, which is used to discharge the charge on C _L1 . When the control signal CON1 is high level, _CL1 is in the charging state; when the control signal CON1 is low level, _CL1 is in the discharging state. One end of C _L1 is connected to the input of voltage buffer A ₁ at the same time. A ₁ is specifically a voltage follower circuit composed of an AD8510 operational amplifier. The function of this circuit is to transfer the terminal voltage of C _L1 to the subsequent stage and block it. The influence of the input impedance of the stage circuit on the previous stage circuit. The output of A ₁ is connected to the second analog switch S ₃ , whose model is ADG1412. The power reference ground is used as another input to connect the third analog switch S ₅ , whose model is ADG1411, and a first-order RC filter circuit composed of RL3 and CL3 is placed at the output of S ₅ . ADG1412 and ADG1411 are analog switching devices with opposite control logic. When the two devices are controlled by the same control signal CON3, at any time, the combined output voltage V _L1 of S ₃ and S ₅ is the charging voltage or ground potential of C _L1 any one of.

In the second digitally controlled ramp voltage generator, the components used are exactly the same as those in the first digitally controlled ramp voltage generator, but the logic level of the control signal CON2 is opposite to that of CON1; the logic level of the control signal CON4 is opposite to that of CON3.

In the proportional adding amplifier, the operational amplifier A3 is AD8510; the resistor R _H is 50Ω, the resistor R _L1 and the circuit R _L2 are 625kΩ, which is equivalent to adding the compensation signal to the main signal in a ratio of 1:12500; R1 is 10kΩ, R2 is 0Ω, that is, the overall output is unit gain after addition.

In this embodiment, the microcontroller GD32F103 sends code values to DACH, DACL1, and DACL1 through the SPI digital bus with a 5 μs cycle and refreshes the cycle. At the same time, it sends CON1, CON2, CON3, and CON4 control signals through digital IO. The control timing is as follows As shown in Figure 3. The two compensation signals obtained are two signals in which the ramp waveform and the ground potential alternate as shown. These two signals are scaled and added to the main signal V _H to obtain the voltage signal shown as V _out . V _out is connected to the voltage-controlled current source as the control voltage, and finally outputs the required current signal.

Claims (5)

1. The utility model provides a precision current source device based on digital regulation and control slope compensation which characterized in that: the digital control system comprises a microcontroller, a voltage type digital-to-analog converter, two paths of digital control slope voltage generators with the same topological structure, a proportional addition amplifier and a voltage-controlled current source, wherein the two paths of digital control slope voltage generators with the same topological structure comprise a first digital control slope voltage generator and a second digital control slope voltage generator;

the microcontroller is connected with the voltage type digital-to-analog converter through a digital bus, the microcontroller is connected with the two paths of digital-to-analog slope voltage generators through the digital bus, and the voltage type digital-to-analog converter and the two paths of digital-to-analog slope voltage generators are respectively connected with three input ends of the proportional addition amplifier; the output end of the proportional addition amplifier is connected with the input end of the voltage-controlled current source; the voltage type digital-analog converter, the two paths of digital-control slope voltage generators and the proportional addition amplifier form a voltage signal generating unit which can be controlled digitally and has slope compensation;

the digital control slope voltage generator is used for generating signals with mutually alternating slope waveforms and ground potential, the signals generated by the two paths of digital control slope voltage generators are opposite, the type of a device used in the second digital control slope voltage generator is completely the same as that of a device corresponding to the first digital control slope voltage generator, but the logic level of a control signal CON2 of a first analog switch in the second digital control slope voltage generator is opposite to that of a control signal CON1 of a first analog switch in the first digital control slope voltage generator; the logic level of the control signal CON4 of the second analog switch in the second numerical control slope voltage generator is opposite to the control signal CON3 of the second analog switch in the first numerical control slope voltage generator;

the numerical control slope voltage generator comprises a numerical control current source, a charging capacitor, a first analog switch, a voltage buffer, a second analog switch and a third analog switch, and the specific structure is as follows:

the output end of the numerical control current source is connected with the first end of the charging capacitor, and charges are injected into the charging capacitor;

the second end of the charging capacitor is connected with a reference point to provide a reference potential for charging voltage;

the input end of the first analog switch is connected with the first end of the charging capacitor, and the output end of the first analog switch is connected to the reference point to provide a charge discharging path for the charging capacitor;

the input end of the voltage buffer is connected with the first end of the charging capacitor, and the charging voltage is buffered to the output end of the voltage buffer;

the input end of the second analog switch is connected with the output end of the voltage buffer, and the charging voltage is conducted to the output end of the numerical control slope voltage generator in a time-sharing way;

the input end of the third analog switch is connected with a reference point, and the reference potential is conducted to the output end of the numerical control slope voltage generator in a time-sharing way;

the second analog switch and the third analog switch are analog switches with opposite control logic and are controlled by the same signal.

2. The precision current source device based on digital regulation and slope compensation according to claim 1, wherein: the digital control current source is a multiplication digital-to-analog converter.

3. The precision current source device based on digital regulation and slope compensation according to claim 1, wherein: the second analog switch and the third analog switch are single pole single throw analog switches.

4. The precision current source device based on digital regulation and slope compensation according to claim 1, wherein: the voltage buffer is a voltage follower formed by an operational amplifier.

5. The precision current source device based on digital regulation slope compensation according to any one of claims 1 to 4, wherein: the output end of the third analog switch is also provided with a first-order RC filter circuit.