JP4972856B2 - Source identification method of electromagnetic interference signal - Google Patents

Description

  The present invention relates to a method for specifying an electromagnetic wave interference signal generation source suitable for specifying an electromagnetic wave interference signal generation source of an electronic apparatus having a digital circuit.

  In general, most electromagnetic interference signals (EMI) generated by the operation of an electronic device having a digital circuit are caused by a fundamental wave of a rectangular wave typified by a clock signal or a digital transmission signal and its harmonics.

  An electronic device having a digital circuit in recent years is constituted by a plurality of functional modules as shown in FIG. 6, and in this case, operates with clock signals having a plurality of frequencies. These clock signals having a plurality of frequencies are usually generated by multiplying or dividing one frequency.

  For this reason, the electromagnetic wave interference signal (EMI) generated by the operation of this digital circuit is often intricately superimposed with a fundamental wave or its harmonics by a clock signal having a plurality of frequencies or a digital transmission signal synchronized therewith. ing.

  In general, countermeasures against electromagnetic interference proceed while investigating the source and transmission path of the electromagnetic interference signal. As a method of investigating the source of this electromagnetic interference signal, as shown in FIG. 6, a current having a frequency that is a countermeasure against electromagnetic interference flowing on a board, chassis, or cable using an inspection probe 1 such as an electric field probe or a current probe. Can be used.

Further, an electromagnetic radiation measurement method as described in Patent Document 1 has been proposed.
JP 2001-343409 A

  By the way, for example, as shown in FIG. 6, when investigating the source 2 and the transmission path of the electromagnetic wave interference signal having the frequency f1, the clock signal frequencies of the other functional modules 3, 4 and 5 are f2, f3. And f4, when the higher harmonics overlap with the frequency f1 of the electromagnetic interference signal to be investigated as f1 = 2 × f2 = 3 × f3 = 4 × f4, the frequency f1 of this electromagnetic interference signal and other It is impossible to distinguish between harmonics 2 × f2, 3 × f3, 4 × f4, and a plurality of sources of electromagnetic interference signals and transmission paths are observed in a complex manner. It is difficult to specify the transmission path, and there is a disadvantage that it takes a long time to investigate the source of the electromagnetic interference signal.

  Moreover, although the technique of patent document 1 can measure an electromagnetic interference signal, the generation source of the electromagnetic interference signal of the electronic device which has a digital circuit cannot be specified.

  SUMMARY OF THE INVENTION In view of this point, an object of the present invention is to make it possible to identify a source of an electromagnetic wave interference signal relatively easily and in a relatively short time.

The method for identifying the source of the electromagnetic interference signal of the present invention measures the carrier frequency of the electromagnetic interference signal, obtains the time domain information of the electromagnetic interference signal, detects the periodicity from the time domain information, and calculates the frequency of this period obtain a modulation frequency of the amplitude modulation by, resulting frequency domain information of the electromagnetic interference signal at a frequency greater range than twice the modulation frequency sidebands indicating the modulation frequency is present in the frequency area information And if present, measure the frequency and level of this sideband and the carrier wave of this electromagnetic interference signal, convert this frequency and level to the modulation degree and modulation frequency as modulation information, Based on this modulation information, the source of the electromagnetic wave interference signal is specified.

  According to the present invention, the modulation information of the amplitude modulation contained in the electromagnetic interference signal is obtained, and the source of the electromagnetic interference signal is specified based on this modulation information. Even when the frequency harmonics of the module clock signal are superimposed, the source of the electromagnetic interference signal can be distinguished, and the source of the electromagnetic interference signal can be identified relatively easily and in a relatively short time. it can.

  Hereinafter, an example of the best mode for carrying out the electromagnetic wave interference signal generation source specifying method of the present invention will be described with reference to the drawings.

  FIG. 2 shows a configuration example for carrying out the electromagnetic wave interference signal generation source specifying method according to the present example. In FIG. 2, 10 is a facility for conducting electromagnetic wave interference evaluation and electromagnetic wave interference countermeasure examination, for example, an anechoic chamber.

  In this example, an electronic device, that is, a device under test 11 for specifying the source of the electromagnetic wave interference signal as shown in FIG.

  An antenna 12 for detecting an electromagnetic interference signal generated by the device under test 11 is provided at a predetermined position in the anechoic chamber 10, and a detection signal such as an electromagnetic interference signal from the antenna 12 is supplied to the anechoic chamber 10. It supplies to the measurement system 13 provided outside.

  In the study on countermeasures against electromagnetic interference, a device that indirectly evaluates electromagnetic interference signals as a common mode current or a common mode voltage, such as an evaluation device using a Workbench Faraday Cage or a current probe, may be used instead.

  The measurement system 13 includes a spectrum analyzer, an electromagnetic wave interference signal (EMI) receiver, a high frequency (RF) amplifier, a high frequency (RF) switch, and the like, and is controlled by a control device 14 such as a computer. In this case, the interface of the measurement system 13 is often automatically controlled via a GPIB (General Purpose Interface Bus) or the like.

  The control device 14 composed of a computer or the like controls the anechoic chamber 10 and the measurement system 13 through GPIB or the like, collects and analyzes the data measured by the measurement system 13, and uses the flowchart shown in FIG. The signal source identification method is executed. In FIG. 2, reference numeral 15 denotes a monitor for performing various displays.

  In the flowchart of FIG. 1, after the start, first, in step S1, the frequency fe of the electromagnetic wave interference signal to be measured is defined (set) in the spectrum analyzer which is a measuring instrument. The frequency fe of the electromagnetic wave interference signal is frequency data obtained from spectrum data obtained by normal evaluation based on the EMI standard as shown in FIG. FIG. 3 shows an example of spectrum data of 30 MHZ to 1 GHz based on the EMI standard. In FIG. 3, the line a is a standard value.

  In step S1, the spectrum analyzer defines (sets) a sideband measurement frequency upper limit fsmax and a sideband measurement frequency lower limit fsmin. The frequency upper limit fsmax and the frequency lower limit fsmin are determined from the performance of the measuring instrument and the time taken for measurement. Generally, the frequency lower limit fsmin is defined as several KHZ to several tens KHZ, and the frequency upper limit fsmax is defined as several hundred KHZ. Set).

  Thereafter, the carrier frequency fc of the electromagnetic wave interference signal is measured (step S2). This carrier frequency fc is the center frequency of the frequency fe of the electromagnetic interference signal, and can be obtained by measuring the frequency fe of the electromagnetic interference signal in detail.

  Next, in step S3, the SPAN (span, measurement frequency range) of the spectrum analyzer is set to “0” at the frequency fe of the electromagnetic wave interference signal to be measured, the frequency is specified, and the scanning time SWT (Sweep Time) Is set to an arbitrary time during which the frequency upper limit fsmax can be sufficiently measured. For example, 1 / (2 × fsmax) or more.

  This is because, in this example, the frequency upper limit fsmax is changed from the scan time SWT at which the frequency lower limit fsmin can be measured to the scan time SWT at which the frequency lower limit fsmin can be measured. First, the frequency lower limit fsmin is set to a scanning time SWT at which sufficient measurement is possible.

  Next, the resolution bandwidth (Resolution Band Width) of the spectrum analyzer, which is a measuring instrument, is adjusted to a value that can best measure the electromagnetic wave interference signal to be measured (step S4).

  Next, in order to remove noise from the measurement waveform, the VBW (Video Band Width) of this spectrum analyzer is set to 20 ÷ SWT, for example. This means 20 times the 1 / SWT (HZ), and is generally set to about 10 to 40 times (step S5).

  The time domain information (time domain data) of the electromagnetic wave interference signal is acquired by the spectrum analyzer in the above state (step S6). The time width measured in step S6 is set so that the set frequency lower limit fsmin and frequency upper limit fsmax can be measured.

  The shortest time width is set to a range that can sufficiently cover the frequency fe of the electromagnetic wave interference signal to be measured, for example, 1 / fsmax × 0.8, and the longest time width, for example, 1 / fsmin × 1.5.

  In this case, when a measuring instrument (spectrum analyzer) capable of simultaneously measuring both the lower frequency limit fsmin and the upper frequency limit fsmax can be used, one measurement may be performed if there is little variation.

  However, if this cannot be realized, the observation time region is divided into a plurality of times with a time width corresponding to the electromagnetic wave interference signal frequency to be measured.

  For the time domain information of the electromagnetic interference signal obtained in step S6, for example, an electromagnetic interference signal having a horizontal axis as a time axis and a vertical axis as a level as shown in FIG. 4 is obtained.

Next, it is determined (detected) whether the time domain information of the electromagnetic wave interference signal as shown in FIG. 4 acquired in step S6 has periodicity (step S7).
When periodicity is detected in step S7, the frequency 1 / TS = fs of the period TS can be calculated to obtain amplitude modulation frequency information, and this frequency information is stored as periodic data (step S8). . In this case, there may be a plurality of periods TS. In this way, it is possible to recognize the modulation frequency (possibly multiple) originating from the same source.

  When the time domain information of the electromagnetic wave interference signal is the example of FIG. 4, there are two periods of TS1 and TS2, and the modulation frequencies fs1 = 1 / TS1 and fs2 = 1 / TS2 of the periods TS1 and TS2 are calculated. Is stored (stored) in the memory.

  Thereafter, the scanning time SWT of the spectrum analyzer is doubled (step S9). If no periodicity is detected in the time domain information (time domain data) of the electromagnetic wave interference signal in step S7, the process proceeds to step S9, and then it is determined whether or not the doubled scanning time SWT is smaller than 1 / fsmin. If it is smaller, step S5, step S6, step S7, step S8, step S9, and step S10 are repeated to store the modulation frequency fs = 1 / TS of the period TS.

  When the spectrum analyzer scanning time SWT is greater than 1 / fsmin in step S10, it is determined whether there is periodic data stored in step S8 (step S11). If there is no stored periodic data, The process ends with no modulation information (step S12).

  When there is a modulation frequency fs = 1 / TS of amplitude modulation which is the periodic data of the period TS stored in step S11, the SPAN of this spectrum analyzer is set slightly larger than 2 × fs and the resolution bandwidth RBW is set to SPAN / 20. (Step S13), and then, with this spectrum analyzer, as shown in FIG. 5, the narrow-band frequency domain information of the electromagnetic wave interference signal is captured, and the sideband corresponding to the frequency fs of the period TS is extracted. It is confirmed whether or not the modulation frequency fs stored in step S8 on the acquired electromagnetic interference information, in the example of FIG. 4, the modulation frequencies fs1 and fs2 are present in the frequency domain information of the electromagnetic interference signal as shown in FIG. S14).

  That is, it is matched whether or not the sidebands indicating the modulation frequencies obtained from the time domain information, for example, the modulation frequencies fs1 and fs2 are present in the frequency domain information. In the example of FIG. 5, it can be confirmed that the sideband 1 (fc−fs1, fc + fs1) and the sideband 2 (fc−fs2, fc + fs2) exist.

  Thus, by extracting the frequency domain information and the modulation frequency fs of the measurement result of the time domain information, it is possible to improve the extraction accuracy of the modulation frequency of the electromagnetic wave interference signal.

  In step S14, when the sideband indicating the modulation frequency fs obtained from the time domain information of the electromagnetic wave interference signal is also present on the frequency domain information of the electromagnetic wave interference signal, the sideband (fc-fs, fc + fs) and the frequency and level of the carrier wave fc are measured in detail, and the modulation degree and modulation frequency, which are modulation information, are converted (step S15).

  The modulation degree and the modulation frequency, which are modulation information of the electromagnetic wave interference signal, are obtained, and the extraction of the modulation information is completed (step S16).

  In this example, the generation source of the electromagnetic wave interference signal of the electronic device as shown in FIG. 6 is specified based on this modulation information.

  According to this example, the modulation information of the amplitude modulation included in the electromagnetic wave interference signal is obtained from the time domain information of the electromagnetic wave interference signal, and the source of the electromagnetic wave interference signal is specified based on the modulation information. Even when the frequency of the electromagnetic wave interference signal and the harmonic of the frequency of the clock signal of another functional module are superimposed, the source of the electromagnetic wave interference signal can be distinguished, and the electromagnetic wave interference can be made relatively easily and in a relatively short time. The source of the signal can be identified.

  Of course, the present invention is not limited to the above-described examples, and various other configurations can be adopted without departing from the gist of the present invention.

It is a flowchart with which description of the example of the best form for implementing the source identification method of the electromagnetic wave interference signal of this invention is provided. It is a block diagram which shows the example of the structure system for implementing FIG. It is a diagram with which it uses for description of this invention. It is a diagram with which it uses for description of the example of this invention. It is a diagram with which it uses for description of the example of this invention. It is a block diagram with which it uses for description of the conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Anechoic chamber, 11 ... Device under test, 12 ... Antenna, 13 ... Measurement system, 14 ... Control apparatus

Claims (1)

Measure the carrier frequency of the electromagnetic interference signal,
Obtain time domain information of the electromagnetic interference signal,
From the time domain information, the periodicity is detected, and the modulation frequency of the amplitude modulation is obtained by calculating the frequency of the period ,
The resulting frequency domain information of the electromagnetic interference signal at a frequency greater range than twice the modulation frequency,
Matching whether or not a sideband indicating the modulation frequency is present in the frequency domain information, and if present, measuring the frequency and level of the sideband and the carrier wave of the electromagnetic interference signal, The level is converted into the modulation degree and modulation frequency, which is modulation information,
An electromagnetic wave interference signal generation source specifying method for specifying an electromagnetic wave interference signal generation source based on the modulation information.

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