JP2020021139A - Ad conversion device - Google Patents

Abstract

To measure noises in a time period shorter than a prior art and remove noises.SOLUTION: There are provided an input unit 1 to which analog signals of a plurality of channels are input, a switch 2 which outputs one of analog signals input by the input unit 1, an ADC 3 which converts the analog signal output by the switch 2 to a digital signal, a switch control unit 41 which controls the switching operation of the switch 2 so as to output an analog signal in a prescribed cycle for each channel and output analog signals of the plurality of channels between the cycles, and an arithmetic unit 42 which averages digital signals acquired by the ADC 3 for each channel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an AD converter that inputs analog signals of a plurality of channels and performs AD conversion.

  2. Description of the Related Art Conventionally, an AD converter that inputs an analog signal and removes commercial noise added to the analog signal has been known (for example, see Patent Documents 1 and 2). In the technique disclosed in Patent Document 1, on the assumption that the number of channels is one, the measurement (sampling) of an analog signal is performed an integer multiple of 4 at a period of 25 ms, so that the commercial noise added to the analog signal is measured. Has been removed. In the technology disclosed in Patent Document 2, the number, the number of channels, and the number, the scan cycle, the order, and the number of measurement scans of the analog signal of each channel are adjusted to adjust the analog signal of each channel. The added commercial noise is removed.

JP-A-5-296787 JP 2000-278128 A

Here, if the technique disclosed in Patent Document 1 is applied to measurement of multi-channel analog signals, at least (25 ms × 4 × the number of channels) is required until all measured values are determined.
The same applies to the technique disclosed in Patent Literature 2. Assuming that the period of the measurement scan is 25 ms, at least (25 ms × 4 × the number of channels) is required until all measured values are determined. .

Further, in the technology disclosed in Patent Document 2, when an analog signal of a channel including an external noise component other than commercial noise is measured alternately with an analog signal of another channel, the external noise component becomes analog of the other channel. May affect the signal.
Further, in the technique disclosed in Patent Document 2, when there is a channel of an input type to be measured at the same time, an error occurs if measurement of a target analog signal is not performed at the same time. Note that the input type to be measured at the same time includes a ratio input and a differential input.

  The present invention has been made in order to solve the above-described problems, and is an AD converter that inputs analog signals of a plurality of channels. It is an object to provide a simple AD converter.

  An AD converter according to the present invention includes an input unit for inputting analog signals of a plurality of channels, a switch for outputting one of the analog signals input from the input unit, and a digital signal for outputting the analog signal output from the switch. An A / D converter that converts the signals into signals, a switch switching unit that controls a switching operation of a switch so as to output an analog signal at a predetermined cycle for each channel and output analog signals of a plurality of channels during the cycle. An arithmetic unit for averaging the digital signal obtained by the AD converter for each channel.

  According to the present invention, since the configuration is as described above, measurement can be performed in a shorter time and noise can be removed as compared with the related art.

FIG. 1 is a diagram illustrating a configuration example of an AD converter according to Embodiment 1 of the present invention. 6 is a flowchart illustrating an operation example of the AD converter according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a specific example of control of a switch switching operation performed by the switch switching unit according to the first embodiment of the present invention. FIG. 13 is a diagram illustrating a specific example of control of a switch switching operation by a switch switching unit according to Embodiment 2 of the present invention. FIG. 13 is a diagram illustrating a configuration example of an AD converter according to Embodiment 3 of the present invention. FIG. 14 is a diagram illustrating a specific example of control of a switch switching operation performed by a switch switching unit according to Embodiment 3 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of an AD converter according to Embodiment 1 of the present invention.
The AD converter inputs analog signals of a plurality of channels and performs AD (analog-digital) conversion. As shown in FIG. 1, the AD converter includes an input unit 1, a switch 2, an ADC (AD converter) 3, and a control unit 4.

  The input unit 1 inputs analog signals of a plurality of channels. The input unit 1 has a plurality of terminals 11 and a plurality of input circuits 12, as shown in FIG. In FIG. 1, assuming that the AD converter inputs analog signals of four channels (ch1 to ch4), the AD converter has terminals 11a to 11d as terminals 11, and input circuits 12a to 12d as input circuits 12. Is shown. The terminal 11a and the input circuit 12a correspond to ch1, the terminal 11b and the input circuit 12b correspond to ch2, the terminal 11c and the input circuit 12c correspond to ch3, and the terminal 11d and the input circuit 12d correspond to ch4.

  The terminal 11 is connected to an output terminal of a target device (not shown) via a signal line, and receives an analog signal.

  The input circuit 12 is connected to one terminal 11 and performs various processes on an analog signal input to the terminal 11. The processing performed by the input circuit 12 includes an amplification processing using an amplification unit and a filtering processing using an analog filter. Note that the input circuit 12 is not an essential component of the AD converter.

  The switch 2 is controlled by the control unit 4 (a switch switching unit 41 to be described later) to control the analog signal (an analog signal subjected to various processes by the input circuits 12a to 12d in FIG. 1) input from the input unit 1. Is output.

  The ADC 3 converts the analog signal output from the switch 2 into a digital signal.

  The control unit 4 controls the switching operation of the switch 2 and obtains a digital signal from which noise has been removed based on the digital signal obtained by the ADC 3. The control unit 4 includes a switch switching unit 41 and a calculation unit 42, as shown in FIG.

  The switch switching unit 41 controls the switching operation of the switch 2 so as to output an analog signal at a predetermined cycle for each channel and to output analog signals of a plurality of channels during the cycle. In the first embodiment, the cycle of outputting the analog signal of each channel, the order of outputting the analog signal of each channel, and the number of outputting the analog signal of each channel are set in advance.

  In the following, it is assumed that the switch switching unit 41 controls the switching operation of the switch 2 so that the period is set to 25 ms and the analog signal is output an integral multiple of 4 for each channel. Further, at this time, the switch switching unit 41 may control the switching operation of the switch 2 so that the output intervals of the analog signals of a plurality of channels output during the period are equal.

  The arithmetic unit 42 averages the digital signal obtained by the ADC 3 for each channel.

  The control unit 4 is realized by a processing circuit such as a system LSI (Large Scale Integration) or a CPU (Central Processing Unit) that executes a program stored in a memory or the like.

Next, an operation example of the AD converter according to the first embodiment will be described with reference to FIG.
In the operation example of the AD converter, first, the input unit 1 inputs analog signals of a plurality of channels (step ST1).

  Next, the switch 2 outputs one of the analog signals input from the input unit 1 under the control of the switch switching unit 41 (step ST2). A specific example of the control of the switching operation of the switch 2 by the switch switching unit 41 will be described later.

  Next, the ADC 3 converts the analog signal output from the switch 2 into a digital signal (step ST3).

  Next, the arithmetic unit 42 averages the digital signal obtained by the ADC 3 for each channel (step ST4). Hereinafter, the operation principle of the arithmetic unit 42 will be described. Hereinafter, a case where the AD converter measures (samples) the analog signal of one channel four times every 25 ms will be described.

  In the AD converter, the switch 2, the ADC 3, and the arithmetic unit 42 measure an analog signal for one channel every 25 ms, and calculate an average of the measured data (digital signals) every four collections. As a result, the sum of the commercial noises included in the above four measurement data becomes 0, regardless of whether the commercial power supply used by the target device is 50 Hz or 60 Hz. As a result, commercial noise is removed from the measurement data finally obtained by the AD converter.

Here, the commercial noise is represented by the following equation (1). In Equation (1), NZ represents commercial noise, Em represents the maximum value of commercial noise, ω represents angular velocity, θ represents a reference time, t represents time, and f represents the frequency of the commercial power supply. .
NZ = Esinω (θ + t)
= Emsin2πf (θ + t) (1)

When the frequency of the commercial power supply was 50 Hz, _{NZ 50} is the sum of the commercial noise included in the four measurement data for each 25ms is expressed by the following formula (2).
NZ ₅₀ = Emsin100π (θ + 0) + Emsin100π (θ + 0.025) + Emsin100π (θ + 0.05) + Emsin100π (θ + 0.075) (2)

When developing equation (2), _{NZ 50} by the following equation (3) becomes zero.
NZ ₅₀ = Emsin (100πθ + 0) + Emsin (100πθ + 2.5π) + Emsin (100πθ + 5π) + Emsin (100πθ + 7.5π)
= Emsin100πθcos0 + Emcos100πθsin0 + Emsin100πθcos2.5π + Emcos100πθsin2.5π + Emsin100πθcos5π + Emcos100πθsin5π + Emsin100πθcos7.5π + Emcos100πθsin.7.
= Emsin100πθ × 1 + Emcos100πθ × 0 + Emsin100πθ × 0 + Emcos100πθ × 1 + Emsin100πθ × (-1) + Emcos100πθ × 0 + Emsin100πθ × 0 + Emcos100πθ × (-1)
= Emsin100πθ + Emcos100πθ × 1−Emsin100πθ−Emcos100πθ
= 0 (3)

When the frequency of the commercial power supply is 60 Hz, NZ ₆₀ , which is the sum of the commercial noises included in the four measurement data every 25 ms, is expressed by the following equation (4).
NZ ₆₀ = Emsin120π (θ + 0) + Emsin120π (θ + 0.025) + Emsin120π (θ + 0.05) + Emsin120π (θ + 0.075) (4)

Then, when Expression (4) is expanded, NZ ₆₀ becomes 0 as in Expression (5) below.
NZ ₆₀ = Emsin (120πθ + 0) + Emsin (120πθ + 3π) + Emsin (120πθ + 6π) + Emsin (120πθ + 9π)
= Emsin120πθcos0 + Emcos120πθsin0 + Emsin120πθcos3π + Emcos120πθsin3π + Emsin120πθcos6π + Emcos120πθsin6π + Emsin120πθcos9π + Emcos120πθsin9π
= Emsin120πθ × 1 + Emcos120πθ × 0 + Emsin120πθ × (-1) + Emcos120πθ × 0 + Emsin120πθ × 1 + Emcos120πθ × 0 + Emsin120πθ × (-1) + Emcos100πθ × 0
= Emsin120πθ-Emsin120πθ + Emsin120πθ-Emsin120πθ
= 0 (5)

In the above description, the case where the AD converter obtains the average of four measurement data each time it is collected has been described. On the other hand, the same applies to the case where the AD converter obtains the average every time the measurement data is collected by an integral multiple of 4.
As described above, the arithmetic unit 42 averages the digital signal obtained by the ADC 3 for each channel, so that commercial noise is removed from the averaged digital signal.

Next, a specific example of the control of the switching operation of the switch 2 by the switch switching unit 41 in the first embodiment will be described with reference to FIG. FIG. 3 shows a case where the number of channels is four (ch1 to ch4), and the AD converter measures the analog signal four times every 25 ms for each channel to remove commercial noise. In FIG. 3, reference numeral 101 denotes a waveform of a 50 Hz commercial noise, and reference numeral 102 denotes a waveform of a 60 Hz commercial noise.
In FIG. 3, the switch switching unit 41 outputs the analog signal at a period of 25 ms for each channel and sequentially outputs the analog signals of four channels every 6.25 ms during the period of 25 ms. Is controlling.

  As a result, as shown in FIG. 3, the ADC 3 measures the analog signal of ch1 at 0 ms, measures the analog signal of ch2 at 6.25 ms, and measures the analog signal of ch3 at 12.5 ms as the first measurement. The analog signal of ch4 is measured at 18.75 ms. The ADC 3 measures the analog signal of ch1 at 25 ms, measures the analog signal of ch2 at 31.25 ms, measures the analog signal of ch3 at 37.5 ms, and measures the ch4 analog signal at 43.75 ms as the second measurement. Measure the analog signal of As a third measurement, the ADC 3 measures an analog signal of ch1 at 50 ms, measures an analog signal of ch2 at 56.25 ms, measures an analog signal of ch3 at 62.5 ms, and measures ch4 at 68.75 ms. Measure the analog signal of The ADC 3 measures the analog signal of ch1 at 75 ms, measures the analog signal of ch2 at 81.25 ms, measures the analog signal of ch3 at 87.5 ms, and measures the ch4 analog signal at 93.75 ms as the fourth measurement. Measure the analog signal of

Thereafter, the arithmetic unit 42 averages the four digital signals obtained by the ADC 3 for each channel.
Thereby, the AD converter according to the first embodiment can remove commercial noise added to an analog signal for each channel. Further, in the example of FIG. 3, the AD converter according to the first embodiment requires only (25 ms × 4) time until all measured values are determined, so that the measurement can be performed in a shorter time than in the related art. .

  In FIG. 3, the AD converter sequentially measures the analog signals of four channels at equal intervals (intervals of 6.25 ms) during a period of 25 ms. Thus, the AD converter according to the first embodiment can reduce the influence of the analog signal on the analog signal of another channel.

  FIG. 3 shows a case where the AD converter measures the analog signal four times every 25 ms for each channel to remove commercial noise. However, the noise to be removed in the AD converter is not limited to commercial noise, and other noises can be removed or reduced by changing the period.

  As described above, according to the first embodiment, the AD converter outputs the input unit 1 for inputting analog signals of a plurality of channels and one of the analog signals input by the input unit 1. A switch 2; an ADC 3 for converting an analog signal output from the switch 2 into a digital signal; and outputting an analog signal at a predetermined period for each channel and outputting analog signals of a plurality of channels during the period. , A switching unit 41 for controlling the switching operation of the switch 2, and an arithmetic unit 42 for averaging the digital signal obtained by the ADC 3 for each channel. Thereby, the AD converter according to the first embodiment can measure and remove noise in a shorter time than the conventional technology.

Embodiment 2 FIG.
In the second embodiment, when there is a channel that easily contains an external noise component other than the noise to be removed (commercial noise or the like), the AD converter separates the analog signal of the channel from the analog signal of another channel. This shows the case where measurement is performed using
The configuration example of the AD converter according to the second embodiment is the same as the configuration example of the AD converter according to the first embodiment shown in FIG.

  In the second embodiment, the switch switching unit 41 controls the switching operation of the switch 2 so that an analog signal of a specific channel is output separately from an analog signal of another channel. Here, the specific channel is a channel that easily contains an external noise component other than the noise to be removed, and is set in advance in the second embodiment.

Next, a specific example of the control of the switching operation of the switch 2 by the switch switching unit 41 in the second embodiment will be described with reference to FIG. FIG. 4 shows a case where the number of channels is four (ch1 to ch4), and the AD converter measures the analog signal four times every 25 ms for each channel to remove commercial noise. In FIG. 4, ch4 is a channel that is likely to contain extraneous noise components other than commercial noise.
In FIG. 5, first, the switch switching unit 41 outputs an analog signal at a period of 25 ms for each of the channels ch1 to ch3, and outputs a three-channel analog signal every 6.25 ms during the period of the 25 ms. , The switching operation of the switch 2 is controlled. Thereafter, the switch switching unit 41 controls the switching operation of the switch 2 so as to output an analog signal at a cycle of 25 ms for ch4.

  As a result, as shown in FIG. 4, the ADC 3 first measures the ch1 analog signal at 0 ms and measures the ch2 analog signal at 6.25 ms as the first measurement for ch1 to ch3. The analog signal of ch3 is measured at 5 ms. The ADC 3 measures the analog signal of ch1 at 25 ms, measures the analog signal of ch2 at 31.25 ms, and measures the analog signal of ch3 at 37.5 ms as the second measurement. As a third measurement, the ADC 3 measures the analog signal of ch1 at 50 ms, measures the analog signal of ch2 at 56.25 ms, and measures the analog signal of ch3 at 62.5 ms. As the fourth measurement, the ADC 3 measures the analog signal of ch1 at 75 ms, measures the analog signal of ch2 at 81.25 ms, and measures the analog signal of ch3 at 87.5 ms. Thereafter, the ADC 3 measures the first analog signal at 100 ms, measures the second analog signal at 125 ms, measures the third analog signal at 150 ms, and measures the fourth analog signal at 175 ms for ch4. I do.

  As described above, according to the second embodiment, the switch switching unit 41 controls the switching operation of the switch 2 so as to output the analog signal of a specific channel separately from the analog signals of other channels. . Accordingly, in addition to the effect of the first embodiment, when there is a channel that easily contains an external noise component other than the noise to be removed, the AD converter according to the second embodiment can output analog signals of other channels. It is possible to reduce the influence of the external noise component.

Embodiment 3 FIG.
In the third embodiment, a case will be described in which, when there is a channel of the input type to be measured at the same time, the AD converter performs measurement of the analog signal of the target channel at the same time.
An example of the configuration of the AD converter according to the third embodiment is as shown in FIG. In FIG. 5, assuming that ch1 and ch2 are a pair and ch3 and ch4 are a pair, the AD converter has terminals 11a and 11b as terminals 11 and input circuits 12a to 12c as input circuits 12. The case where it has is shown. The terminal 11a and the input circuit 12a correspond to ch1 and ch2, the terminal 11b corresponds to ch3 and ch4, the input circuit 12b corresponds to ch3, and the input circuit 12c corresponds to ch4. In the AD converter according to the third embodiment shown in FIG. 5, the operation of each unit other than switch switching unit 41 is basically the same as the operation of each unit of the AD converter according to the first embodiment shown in FIG. And the description is omitted.

  In the third embodiment, the switch switching unit 41 controls the switching operation of the switch 2 so as to output each analog signal of a specific plurality of channels. Here, the specific channel is a channel of an input type to be measured at the same time, and is set in advance in the third embodiment.

Next, a specific example of control of the switching operation of the switch 2 by the switch switching unit 41 according to the third embodiment will be described with reference to FIG. FIG. 6 shows a case where the number of channels is four (ch1 to ch4), and the AD converter measures the analog signal four times every 25 ms for each channel to remove commercial noise. FIG. 6 shows a case where ch1 and ch2 are pairs and ch3 and ch4 are pairs.
In FIG. 6, first, the switch switching unit 41 outputs an analog signal at a period of 25 ms for each of the channels ch1 and ch2, and outputs an analog signal of two channels at a period of 12.5 ms during the period of 25 ms. , The switching operation of the switch 2 is controlled. Thereafter, the switch switching unit 41 outputs the analog signal for each of the channels ch3 and ch4 at a period of 25 ms for each channel, and outputs the analog signal of two channels every 12.5 ms during the period of 25 ms. Switching operation is controlled.

  As a result, as shown in FIG. 6, the ADC 3 first measures the ch1 analog signal at 0 ms and measures the ch2 analog signal at 12.5 ms as the first measurement for ch1 and ch2. The ADC 3 measures the analog signal of ch1 at 25 ms and the analog signal of ch2 at 37.5 ms as the second measurement. The ADC 3 measures the analog signal of ch1 at 50 ms and measures the analog signal of ch2 at 62.5 ms as the third measurement. The ADC 3 measures the analog signal of ch1 at 75 ms and the analog signal of ch2 at 87.5 ms as the fourth measurement. Thereafter, the ADC 3 measures the ch3 analog signal at 100 ms and measures the ch4 analog signal at 112.5 ms as the first measurement for ch3 and ch4. The ADC 3 measures the analog signal of ch3 at 125 ms and measures the analog signal of ch4 at 137.5 ms as the second measurement. The ADC 3 measures the analog signal of ch3 at 150 ms and the analog signal of ch4 at 162.5 ms as the third measurement. The ADC 3 measures the analog signal of ch3 at 175 ms and measures the analog signal of ch4 at 187.5 ms as the fourth measurement.

  As described above, according to the third embodiment, the switch switching unit 41 controls the switching operation of the switch 2 so as to output the analog signals of a plurality of specific channels. Accordingly, in addition to the effects of the first embodiment, when there is a channel of the input type to be measured at the same time, the AD conversion device according to the third embodiment has an error due to a shift in measurement timing and an error of another channel. The effect of the analog signal can be suppressed.

  In the first to third embodiments, the case where the switch switching unit 41 controls the switching operation of the switch 2 based on the information set in advance has been described. However, the invention is not limited thereto, and the switch switching unit 41 may automatically control the switching operation of the switch 2. In this case, the switch switching unit 41 determines the presence or absence and type of noise for each channel based on the digital signal obtained by the ADC 3, and controls the switching operation of the switch 2 based on the determination result. Also in this case, the initial operation of the switch switching unit 41 controls the switching operation of the switch 2 based on the information set in advance.

  In the present invention, any combination of the embodiments, a modification of an arbitrary component of each embodiment, or an omission of an arbitrary component in each embodiment is possible within the scope of the invention. .

1 input unit 2 switch 3 ADC
4 control unit 11 terminal 12 input circuit 41 switch switching unit 42 arithmetic unit

Claims (6)

An input section for inputting analog signals of a plurality of channels,
A switch for outputting one of the analog signals input by the input unit;
An AD converter that converts an analog signal output by the switch into a digital signal;
A switch switching unit that controls a switching operation of the switch, so as to output an analog signal at a predetermined cycle for each channel and output analog signals of a plurality of channels during the cycle.
An arithmetic unit for averaging the digital signal obtained by the AD converter for each channel. The AD converter according to claim 1, wherein the switch switching unit controls the switching operation of the switch such that the cycle is 25 ms and an analog signal is output an integral multiple of 4 for each channel. . The said switch change part controls the switch operation | movement of the said switch so that the output interval of the analog signal of the some channel output during the said period may be equalized. The Claim 1 or Claim 2 characterized by the above-mentioned. AD converter. 4. The switch according to claim 1, wherein the switch switching unit controls a switching operation of the switch such that an analog signal of a specific channel is output separately from an analog signal of another channel. 5. The AD converter according to claim 1. The said switch switching part controls the switching operation | movement of the said switch so that it may output for every analog signal of a specific some channel. The Claim 1 characterized by the above-mentioned. AD converter. The switch switching unit determines the presence or absence and type of noise for each channel based on a digital signal obtained by the AD converter, and controls the switching operation of the switch based on the determination result. The AD converter according to any one of claims 1 to 5.

Images