CN107907736A - Digitize non-linear simulation front end measuring circuit - Google Patents

Abstract

The present invention relates to digitlization non-linear simulation front end measuring circuit, including：Signal sampling circuit, signal conditioning circuit, measurement range selection unit, drive circuit, AD conversion unit and electrical isolation unit；Measurement range selection unit includes multiple electronic switches, and each signal sampling circuit is connected by a signal conditioning circuit with an electronic switch, and electronic switch is connected by drive circuit with AD conversion unit, and the control terminal of electronic switch is used to be connected with external control system；AD conversion unit is connected with external control system.After signal sampling circuit receives signal, the digital signal of sampling sample is exported to external control system through electrical isolation unit, when the value of the signal currently measured is in measurement range, current electronic switch is kept to turn on, when the signal value currently measured is not in measurement range, current electronic switch is closed, opens the corresponding electronic switch of another range, realize the continuous adjustment to range so that more accurate to measuring.

Description

Digital nonlinear analog front-end measurement circuit

technical field

The invention relates to the technical field of nonlinear measurement, in particular to a digital nonlinear analog front-end measurement circuit.

Background technique

Linear power means that the input current or voltage is a continuous and linear value, while nonlinear power means that the input current or voltage is non-linear or dynamically changing. At present, the measurement of current or voltage cannot be accurately measured for sudden changes or large-scale nonlinear conditions.

In addition, for the measurement of non-linear electricity, the sampling of traditional measurement uses one or more cycles of the linear waveform as the control period of the range adjustment. Since the nonlinear waveform may change dynamically within one cycle, the traditional The measurement circuit cannot accurately measure current or voltage.

Contents of the invention

Based on this, it is necessary to provide a digital nonlinear analog front-end measurement circuit.

A digital nonlinear analog front-end measurement circuit, comprising: multiple signal sampling circuits, multiple signal conditioning circuits, a range selection unit, a drive circuit, an analog-to-digital conversion unit, and an electrical isolation unit;

The range selection unit includes a plurality of electronic switches, each of the signal sampling circuits is connected to the first end of the electronic switch through a signal conditioning circuit, and the second end of the electronic switch is connected through the driving circuit Connected to the input end of the analog-to-digital conversion unit, the control end of the electronic switch is used to connect to the external control system through the electrical isolation unit, and the digital interface signal end of the analog-to-digital conversion unit is used to The isolation unit is connected to an external control system.

Further, the first input end of the drive circuit is respectively connected to the second end of each of the electronic switches, and the second input end of the drive circuit is grounded through a resistor.

Further, the first output terminal and the second output terminal of the driving circuit are respectively connected to the two input terminals of the analog-to-digital conversion unit.

4. The digital nonlinear analog front-end measurement circuit according to claim 1, wherein the electronic switch is a SPST analog switch.

Further, each signal sampling circuit is connected with a sampling resistor.

Further, the resistance values of the sampling resistors are different.

The beneficial effects of the present invention are: when working, one of the multiple electronic switches is controlled to be turned on, and only the current signal or voltage signal sampled by the signal sampling circuit corresponding to the electronic switch is allowed to pass through, and the current signal or voltage signal passes through in turn. The signal conditioning circuit, the driving circuit and the analog-to-digital conversion unit are converted into digital signals and then output to an external control system through electrical isolation. When the value of the measured signal is within the measurement range, keep the current electronic switch on and continue the measurement; when the current measured signal value is not within the measurement range, turn off the current electronic switch and control it through an internal algorithm of the external control system The electronic switch corresponding to the other range is turned on, so as to realize continuous and rapid adjustment of the range, and can adapt to the measurement of nonlinear waveforms, making the measurement of current or voltage more accurate.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings on the premise of not paying creative efforts.

The functional block diagram of the digital nonlinear analog front-end measuring circuit of Fig. 1 one embodiment;

Fig. 2 is the circuit schematic diagram of the digitized nonlinear analog front-end measurement circuit applied to current sampling of an embodiment;

Fig. 3 is the circuit schematic diagram of the digitized nonlinear analog front-end measurement circuit applied to voltage sampling of an embodiment;

Fig. 4 is a schematic diagram of the control flow of the digital nonlinear analog front-end measurement circuit by the external control system.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

It should be understood that the digital nonlinear analog front-end measurement circuit can measure both current signals and voltage signals.

As shown in Figure 1, in one embodiment, a digital nonlinear analog front-end measurement circuit includes: multiple signal sampling circuits, multiple signal conditioning circuits, range selection unit, drive circuit, analog-to-digital conversion unit and electrical isolation unit; the range selection unit includes a plurality of electronic switches, each of the signal sampling circuits is connected to a first end of the electronic switch through a signal conditioning circuit, and the second end of the electronic switch is connected through the The drive circuit is connected to the input end of the analog-to-digital conversion unit, the control end of the electronic switch is used to connect to the external control system through the electrical isolation unit, and the digital interface signal end of the analog-to-digital conversion unit is used to pass through the The electric isolation unit is connected with the external control system.

Specifically, the control end of the electronic switch is used to connect to an external control system after being electrically isolated, and the digital interface signal end of the analog-to-digital conversion unit is used to connect to an external control system through electrical isolation. In other words, the control terminal of the electronic switch is used to connect to an external control system through the electrical isolation unit, and the digital interface signal terminal of the analog-to-digital conversion unit is used to connect to an external control system through the electrical isolation unit.

Specifically, when measuring, one of the multiple electronic switches is turned on, and only the current signal or voltage signal sampled by the signal sampling circuit corresponding to the electronic switch is allowed to pass through, and the current signal or voltage signal passes through the signal conditioning circuit, drive The circuit is converted into a digital signal by an analog-to-digital conversion unit and connected to an external control system after being electrically isolated. When the value of the measured signal is within the measurement range, keep the current electronic switch on and continue the measurement. When the current measured signal value is not within the measurement range, turn off the current electronic switch and control it through an internal algorithm of the external control system Turn on the electronic switch corresponding to another range, so as to realize the continuous and rapid adjustment of the range, and can adapt to the measurement of nonlinear waveform, making the measurement of current or voltage more accurate.

As shown in Figure 2, it is a digital nonlinear analog front-end measurement circuit applied to current sampling according to an embodiment of the present invention, including: multiple signal sampling circuits 210, multiple signal conditioning circuits 220, range selection unit 230, and drive circuit 240 and an analog-to-digital conversion unit 250; the range selection unit includes a plurality of electronic switches 231, and each of the signal sampling circuits 210 is connected to a first end of the electronic switch 231 through a signal conditioning circuit 20, so The second end of the electronic switch 231 is connected to the input end of the analog-to-digital conversion unit 250 through the drive circuit 240, the control end of the electronic switch 231 is used to connect with an external control system, and the analog-to-digital conversion unit The digital interface signal terminal is used to connect with the external control system after being electrically isolated.

Specifically, the analog-to-digital conversion unit may be implemented by using the AD7687 of Analog Devices, which is not limited in this embodiment.

In order to realize electrical isolation, specifically, the control end of the electronic switch is electrically isolated and connected to an external control system, and the digital interface signal end of the analog-to-digital conversion unit is electrically isolated and connected to an external control system. In one embodiment, as shown in FIG. 2, the digital nonlinear analog front-end measurement circuit further includes a first electrical isolation unit 261 and a second electrical isolation unit 262, that is, the electrical isolation unit includes a first electrical isolation unit 261 and a second electrical isolation unit 261. isolation unit 262 . For example, the control terminal of the electronic switch 231 is used to connect to an external control system through the first electrical isolation unit 261, and the digital interface signal terminal of the analog-to-digital conversion unit 250 is used to communicate with the external control system through the second electrical isolation unit 262. Connect with external control system. By using the electrical isolation of the first electrical isolation unit and the second electrical isolation unit, the sampled current or voltage signal can be isolated from the control signal. It is worth mentioning that the first electrical isolation unit and the second electrical isolation unit may be the same circuit unit, or may be two mutually independent circuit units.

Specifically, the first electrical isolation unit and the second electrical isolation unit can be realized by ADuM4400_4401_4402 of Analog Devices or π120A4/π121A4/π122A4 of Rongpai Semiconductor, which is not limited in this embodiment.

Specifically, the analog-to-digital conversion unit includes a control terminal (enable terminal) and a digital interface signal terminal, and the control terminal and the digital communication interface signal terminal of the analog-to-digital conversion unit are connected to an external control system through the electrical isolation unit.

Specifically, the signal sampling circuit is used to connect to the input terminal, and the signal sampling circuit is used to sample the current signal or the voltage signal. For example, each of the signal sampling circuits is connected to a sampling resistor. For example, the input terminal is The measurement input terminal is used to input the sampling signal to the digital nonlinear analog front-end measurement circuit.

The signal conditioning circuit is used to amplify the input signal of the signal sampling circuit to match the impedance of the sampling resistors with different resistance values, and output the signal to the driving circuit through the electronic switch. For example, in one embodiment, the signal conditioning circuit includes an instrumentation amplifier. For example, the signal conditioning circuit includes an instrumentation amplifier and resistors and capacitors connected to the instrumentation amplifier. The connection between the resistor and the capacitor and the instrumentation amplifier can be realized by using existing technologies. For example, the signal conditioning circuit can be realized by AD8237 of ADI Company. This example is not limited. The drive circuit is used to convert the amplified single-ended common-mode input signal into a double-ended differential-mode input signal, and output it to the analog-to-digital conversion unit, and the analog-to-digital conversion unit is used to convert the analog input signal of the drive circuit to The digital signal is electrically isolated and output to an external control system.

In this embodiment, each of the electronic switches is used to have one and only one conduction at any time, or in other words, the control terminal of each of the electronic switches is used to control that one and only one of the electronic switches receives a conduction signal at any time And the electronic switch is turned on, that is, each of the electronic switches is used to conduct one and only one at any moment under the control of the external control system. The control terminal of each electronic switch is used to connect the control signal input terminal corresponding to a range of the external control system, that is, the control terminal of each electronic switch is used to connect the control signal input terminal corresponding to different ranges of the external control system, and each electronic switch corresponds to different volumes.

At any one time, one of the electronic switches is turned on. The control of the turned-on electronic switch may be based on an algorithm in an external control system. The electronic switch is turned on, so that the input signal received by the signal sampling circuit can pass through the signal conditioning circuit, the driving circuit, and be converted into a digital signal by the analog-to-digital conversion unit, and then output to the external control system after being electrically isolated. The digital signal is calculated to detect whether the value of the input signal is within the range corresponding to the electronic switch. When the value of the currently measured signal is within the measurement range, keep the current electronic switch on, that is, continue to send a conduction signal to the control terminal of the current electronic switch, so that the corresponding range of the electronic switch can continue to measure the input signal .

When the value of the currently measured signal is greater than the range corresponding to the electronic switch, a closing signal is sent to the control terminal of the electronic switch, so that the electronic switch is closed, and a signal is sent to the control terminal of the electronic switch corresponding to another larger range. Turn on the signal, so that the electronic switch corresponding to the larger range is turned on, so that the external control system can accurately measure the value of the larger signal; when the value of the currently measured signal is smaller than the range corresponding to the electronic switch, then Send a closing signal to the control terminal of the electronic switch, so that the electronic switch is closed, and send a conduction signal to the control terminal of the electronic switch corresponding to another smaller range, so that the electronic switch corresponding to the smaller range is turned on. Accurately measure the value of smaller signals. By selecting the conduction of the electronic switch, the range of the external control system can quickly correspond to the value of the input signal, so that the value of the input signal is always within the linear range of the analog front-end measurement circuit, thereby effectively improving the measurement accuracy.

Since the external control system continuously receives the input signal, and constantly calculates the value of the input signal, and detects in real time whether the value of the input signal is within the range corresponding to the electronic switch, thereby changing or maintaining the conduction of the electronic switch, enabling Measure the sampling voltage of circuits with different ranges, so that the selected input signal is always maintained within the linear range of the range, making the measurement more accurate, realizing accurate measurement of nonlinear waveforms, making it easier to measure current or voltage Accurate and faster.

For example, multiple signal conditioning circuits have different amplification amplitudes or amplification ranges. In this way, for input signals in different ranges, different signal conditioning circuits can be amplified by different multiples, so that each input signal can be amplified by different multiples. And it is within the same reasonable range after amplification, so as to realize accurate measurement of the input signal.

In addition, for the measurement of a wider range, it can be easily realized by only increasing the number of electronic switches of the range selection unit, increasing the number of corresponding branches, configuring corresponding sampling resistors and the amplification factor of the signal conditioning circuit.

In one embodiment, the first input end of the driving circuit is respectively connected to the second end of each of the electronic switches, and the second input end of the driving circuit is grounded through a resistor. Further, the first output terminal and the second output terminal of the driving circuit are respectively connected to the two input terminals of the analog-to-digital conversion unit.

Specifically, the driving circuit is a fully differential driver. In this embodiment, the driving circuit is a low-noise and low-distortion fully differential amplifier for converting common-mode signals into differential-mode signals. The amplifier has a first input terminal, A second input terminal, a first output terminal and a second output terminal. In this way, the input signal amplified by the signal conditioning circuit is converted from single-ended to differential through the driving circuit.

In order to realize the on and off of the electronic switch, in one embodiment, the electronic switch is a SPST (single-pole single-throw, single-pole single-throw) analog switch, and the control pole of the SPST analog switch is a control terminal, so that the external The control system can control the on-off of the electronic switch by inputting the control signal to the control pole of the electronic switch.

For an embodiment as shown in FIG. 2 , the input of each signal sampling circuit is connected to a sampling resistor. For example, further, the resistance values of the sampling resistors are different. In this way, for different measuring ranges, different signal sampling circuits are connected with sampling resistors of different resistance values, which can effectively adapt to different measuring ranges.

Below is a concrete embodiment:

In this embodiment, the digital nonlinear analog front-end measurement circuit (current sampling) as shown in Figure 2 includes: four signal sampling circuits, four signal conditioning circuits, a range selection unit, a drive circuit, an analog-to-digital conversion unit, a first An electrical isolation unit and a second electrical isolation unit; the range selection unit includes four electronic switches, each of the signal sampling circuits is connected to a sampling resistor, each of the signal sampling circuits is connected to a signal conditioning circuit through a The first end of the electronic switch is connected, the second end of the electronic switch is connected to the input end of the analog-to-digital conversion unit through the drive circuit, and the control end of the electronic switch is connected to the external The control system is connected, and the digital interface signal end of the analog-to-digital conversion unit is connected to the external control system through the second electrical isolation unit.

In this embodiment, the four signal sampling circuits are respectively Is1, Is2, Is3 and Is4, the four signal conditioning circuits are instrumentation amplifiers, the four instrumentation amplifiers are respectively AMP1, AMP2, AMP3 and AMP4, and the four electronic switches are respectively SWITCH1 , SWITCH2, SWITCH3 and SWITCH4, Is1 is connected to SWITCH1 through AMP1, Is2 is connected to SWITCH2 through AMP2, Is3 is connected to SWITCH3 through AMP3, Is4 is connected to SWITCH4 through AMP4, the corresponding range of Is1 is 0 to 1mA, and the corresponding range of Is2 is 1 to 10mA, the range corresponding to Is3 is 10 to 100mA, and the range corresponding to Is4 is 100 to 1000mA. The analog-to-digital conversion unit has four interface signals, namely CNV, SCK, SDI and SDO, wherein CNV is the enable terminal, and SDO is the digital interface signal terminal, and the enable terminal and the digital interface signal terminal are electrically isolated from each other. External control system connection. The external control system sends the CNV signal to the AD conversion unit through the enable end of the AD conversion unit to start the analog-to-digital conversion of the AD conversion unit. After the conversion is completed, a data sample transmission is performed, that is, the converted digital signal Output to external control system through SDO.

When measuring, the input signal is 300mH, one of the electronic switches is turned on, for example, the currently turned on electronic switch is SWITCH2, the signal sampling circuit Is2 is turned on, the external control system sends the CNV signal to the analog-to-digital conversion unit, and the signal sampling circuit Is2 receives After receiving the input signal, the input signal is amplified by the signal conditioning circuit AMP2, differentially converted by the drive circuit DRIVE, and converted by the analog-to-digital conversion unit ADC, and the digital signal is output to the external control system by the SDO of the analog-to-digital conversion unit. The external control system measures that the current current value is greater than 10mA, which is greater than the range 1 to 10mA corresponding to the signal sampling circuit Is2. The external control system controls the electronic switch SWITCH2 to close, and selects the electronic switch SWITCH3 corresponding to a larger range. The external control system controls the electronic switch SWITCH3 Turn on, the input signal is amplified by the signal conditioning circuit AMP3, the differential conversion of the drive circuit and the analog-to-digital conversion of the analog-to-digital conversion unit are converted into digital signals, and the digital signal is output to the external control system by the SDO of the analog-to-digital conversion unit , the external control system measures that the current value is greater than 100mA, which is 10 to 100mA greater than the range corresponding to the signal sampling circuit Is3, and the external control system controls the electronic switch SWITCH3 to close, selects the electronic switch SWITCH4 corresponding to a larger range, and the external control system controls the electronic switch SWITCH4 is turned on. In this way, since the signal sampling circuit Is4 corresponds to a range of 100 to 1000mA, the external control system can accurately detect that the input signal is 300mA.

For example, later, when the value of the input signal changes to 60mA, since the electronic switch SWITCH4 is turned on at this time, and the range corresponding to the signal sampling circuit Is4 is 100 to 1000mA, the external control system measures that the value of the input signal is smaller than the range corresponding to Is4 100 to 1000mA, therefore, the control electronic switch SWITCH4 is closed, and the electronic switch SWITCH3 corresponding to the smaller range is selected, and the external control system controls the electronic switch SWITCH3 to be turned on. Since the range corresponding to the signal sampling circuit Is3 is 10 to 100mA, the value of the input signal is 60mA at The range corresponding to Is3 is within 10 to 100mA, therefore, the external control system can accurately detect that the input signal is 60mA.

Through the above process, the electronic switch is selected to be turned on and off, so as to realize the rapid selection and switching of the range, so that the range can better match the value of the current input signal, and then realize the accurate measurement of the input signal. In addition, since the external control system detects each sampling value in real time, the internal algorithm is used to judge whether the value of the input signal is within the range, so as to realize the real-time adjustment of the range, instead of the traditional judgment on the effective value of multiple cycles , so that the range can be adjusted in real time according to the measured waveform, and can effectively adapt to the measurement of fast-changing nonlinear waveforms, making the measurement of current or voltage more accurate.

In addition, in this embodiment, the input signals of the four signal sampling circuits are respectively Is1, Is2, Is3 and Is4, and are respectively connected to four sampling resistors. The four sampling resistors are respectively Ri1, Ri2, Ri3 and Ri4 sampling resistors, that is, the signal sampling circuit corresponding to the sampling signal Is1 is connected to the sampling resistor Ri1, the signal sampling circuit corresponding to the sampling signal Is2 is connected to the sampling resistor Ri2, and the corresponding signal sampling circuit to the sampling signal Is3 The signal sampling circuit is connected to the sampling resistor Ri3, and the signal sampling circuit corresponding to the sampling signal Is4 is connected to the sampling resistor Ri4.

The technical features of the above-mentioned embodiments can be combined arbitrarily. FIG. 3 is another embodiment applied to voltage sampling. Because only the connection mode of the sampling resistor is different, and the input signal of the voltage sampling is usually large enough, so the range switch is moved before the signal conditioning circuit in Figure 3, and the number of instrumentation amplifiers is saved at the same time. For the sake of concise description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered as within the scope of this specification.

As shown in Figure 4, it is the range control process of the external control system of an embodiment:

Step 1, sending an enable CNV signal.

Send the enable signal CNV to the enable terminal of one of the analog-to-digital conversion units.

Step 2, start ADC conversion.

That is, the analog-to-digital conversion unit starts the analog-to-digital conversion to perform analog-to-digital conversion on the signal.

Step 3, judge that the ADC conversion is completed, if yes, execute step 4, otherwise continue to execute step 2.

That is, it is judged whether the ADC conversion is completed.

Step 4, sending a sample data Sn via SPI communication.

The external control unit receives a digital signal converted by the analog-to-digital conversion unit, and acquires a sample data Sn.

Step five, judge that Sn>Max_n, if yes, select n=n+1 range, and execute step five again, otherwise, execute step six.

To judge whether the sample data is greater than the maximum value of the current range, select the n+1 range, and then make the judgment of Sn>Max_n again, that is, measure with a larger range, otherwise go to step 6.

Step 6, judge Sn<Min_n, if yes, select n=n-1 range, and execute step 6 again, otherwise, execute step 7.

To judge whether the sample data is greater than the minimum value of the current range, it is to select n-1 range, that is, to measure with a smaller range, and to judge again that Sn<Min_n. It is worth mentioning that, in this embodiment, the range corresponding to the n file is smaller than that corresponding to the n+1 file, and the measuring range corresponding to the n file is larger than the n−1 file.

Step 7, turn on the nth switch.

That is to turn on the electronic switch corresponding to the n range, so that the signal sampling circuit, signal conditioning circuit, drive circuit and analog-to-digital conversion unit corresponding to the electronic switch are connected, so as to realize the accuracy of the current signal or voltage signal in the range. Measurement.

Step eight, turn off the CNV signal.

After the measurement is completed, the next group of enable signals CNV is sent to the enable terminal of the analog-to-digital conversion unit, so that the analog-to-digital conversion unit enters the next sampling control cycle.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (6)

1. A digital nonlinear analog front-end measurement circuit, characterized in that, comprises: a plurality of signal sampling circuits, a plurality of signal conditioning circuits, a range selection unit, a drive circuit, an analog-to-digital conversion unit and an electrical isolation unit; The range selection unit includes a plurality of electronic switches, each of the signal sampling circuits is connected to the first end of the electronic switch through a signal conditioning circuit, and the second end of the electronic switch is connected through the driving circuit Connected to the input end of the analog-to-digital conversion unit, the control end of the electronic switch is used to connect to the external control system through the electrical isolation unit, and the digital interface signal end of the analog-to-digital conversion unit is used to The isolation unit is connected to an external control system. 2. The digital nonlinear analog front-end measurement circuit according to claim 1, wherein the first input end of the drive circuit is connected to the second end of each of the electronic switches respectively, and the second end of the drive circuit The input is connected to ground through a resistor. 3. The digital nonlinear analog front-end measurement circuit according to claim 1, characterized in that, the first output terminal and the second output terminal of the driving circuit are respectively connected to the two input terminals of the analog-to-digital conversion unit. 4. The digital nonlinear analog front-end measurement circuit according to claim 1, wherein the electronic switch is a SPST analog switch. 5. The digital non-linear analog front-end measurement circuit according to claim 1, characterized in that each of the signal sampling circuits is connected with a sampling resistor. 6 . The digital nonlinear analog front-end measurement circuit according to claim 5 , wherein the resistance values of each of the sampling resistors are different.