CN101458282B - High-frequency circuit spacing electromagnetic radiation characteristic analyzing and predicting method - Google Patents

Abstract

The invention discloses a method for analyzing and predicting the space electromagnetic radiation characteristics of a high-frequency circuit. The input terminal of the preamplifier is connected to the current probe, and the output terminal is connected to the spectrum analyzer; the current probe is stuck on the cable of the circuit loop for measurement to obtain the common mode current value; according to the common mode current value, the field strength value of the common mode radiation is calculated . The input terminal of the preamplifier is connected to a differential mode probe, and the output terminal is connected to a spectrum analyzer. Use a differential mode probe to clamp on the cable of the circuit loop for measurement; obtain the differential mode current value. Calculate the field strength value of the differential mode radiation according to the differential mode current value. The second step is to clamp the current probe on the ground cable of the circuit under test; divide the ground cable of the circuit into several sections, and then move the position of the current probe on the ground cable to measure the current parameter value of each section of the ground cable , to calculate the value of the electromagnetic field strength in the circuit space. It is simple, fast and practical to analyze and predict the electromagnetic radiation characteristics of high-frequency circuits.

Description

High-frequency circuit spacing electromagnetic radiation characteristic analyzing and predictor method

Technical field

What the present invention relates to is the method for electronic circuit being measured circuit parameter analysis and anticipator circuit near-field thermal radiation characteristic, be based on the high-frequency circuit spacing electromagnetic radiation characteristic analyzing and the predictor method of current measurement specifically, judging and suppress for the mechanism of radiativity electromagnetic interference (EMI) noise provides prerequisite, belongs to the electromagnetic compatibility technology field.

Background technology

The modern power electronic product is just towards microminiaturized, intelligent, the design of system also becomes increasingly complex, add system's parasitic parameter of the speed-sensitive switch generation of on-off element in the power electronic equipment, it is serious further to cause equipment disturbed by conduction interference and radial pattern, and more and more higher to the requirement of system's anti-electromagnetic interference capability.Thereby, in order to save the development time, save development cost, research is absolutely necessary to the product circuit spacing electromagnetic radiation characteristic.

Electromagnetic compatibility standard is the compulsory standard of produce market access at present, and no matter electric and electronic product still is international marketing at home, all must reach corresponding EMC standard and just can sell on market.Therefore, the measurement of electromagnetic interference (EMI) noise emission and inhibition are essential major issues of considering in electric and electronic device design and the manufacture process, at present the mensuration of near-field electromagnetic radiation characteristic is used usually the method for near field electromagnetic field measurement, wherein, " EMSCAN " system is popular on the market near-field electromagnetic radiation measuring system, it mainly is to utilize probe or linear transducer array that the entire circuit plate is scanned, and note the variation of surveying the electromagnetic field that causes because high-frequency current changes, and provide the visual pattern of electromagnetic field space distribution on PCB.Yet this quasi-instrument is all comparatively expensive; medium-sized and small enterprises are difficult to bear; and this type systematic can only provide the result of field intensity size; and can not provide deduction to the radiation characteristic (being common mode radiation or differential mode radiation) of circuit; promptly can not propose guidance instruction, promptly can not infer that the circuit space electromagnetic radiation is radiation-induced by common mode or differential mode by measurement result to the channel radiation cause of failures.In addition, existing radiation EMI measurement mechanism all is based on electromagnetic field measurements, and operability is not strong, brings very big puzzlement often for the operation of measuring.

Summary of the invention

Technical matters to be solved by this invention is to overcome the defective that prior art exists, and has proposed a kind of high-frequency circuit spacing electromagnetic radiation characteristic analyzing and predictor method.The current parameters of the direct metering circuit of this method is by the power relatively and the circuit space electromagnetic field Changing Pattern of common mode in the current parameters analysis circuit or differential mode radiation interference.

High-frequency circuit electromagnetic radiation diagnosis principle based on the circuital current parameter

Be illustrated in figure 1 as the Radiation Emission figure in the high-frequency circuit, wherein circuit loop can cause the Radiation Emission that is similar to coil antenna, and transmission cable can cause the Radiation Emission of short straight antenna.Fig. 2 is the common mode radiation model of circuit, and the field intensity formula of common mode radiation is:

$E_{\mathrm{CM}}=1.256\×{10}^{-6}\frac{\mathrm{Ifdl}}{r}\sin \mathrm{\θ}---\left(1\right)$

Figure 3 shows that the differential mode radiation model of circuit, the field intensity formula of differential mode radiation is:

$E_{\mathrm{DM}}=2.632\&times;{10}^{-14}\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{IdS}}{r}---\left(2\right)$

From formula (1) (2) as can be seen the differential mode radiation maximal value and frequency square, the size of loop area and differential-mode current is directly proportional; The maximal value of common mode radiation is directly proportional with the length of frequency, lead and the size of common mode current.Because the radiation EMI noise in the circuit is caused by common mode current, and the circuit design scheme determines that back frequency f and loop (comprising loop area dS and conductor length dl) also determine thereupon, so as long as the size that measures loop current just can the electromagnetic radiation of decision circuitry in which kind of radiation more intense.

The radiated electric field computing formula of current lead is in the free space:

$E_{\mathrm{\&theta;}}\&ap;j\frac{I1Z_0{\mathrm{\&beta;}}_0\sin \mathrm{\&theta;}}{4\mathrm{\&pi;r}}{e}^{-j{\mathrm{\&beta;}}_{0}r}V/m---\left(3\right)$

Along with the increase of frequency, along the uniformity no longer of the distribution of current on the lead.Lead evenly can be divided into N segment for this reason, adopt the radio-frequency current probe to measure its electric current separately, establish and be respectively I in the centre position of every segment ₁, I ₂I _nAs shown in Figure 4, total space equivalence computation of radiation field is converted into so:

$\left|E_c\right|\&ap;\frac{2\mathrm{\&pi;f}\&times;{10}^{-7}F({\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="H200810242654XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">I</figure-callout>}}_2+...+I_n)l}{3\sqrt{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">r</figure-callout>}}^2+{(H-0.8)}^2}}V/m---\left(4\right)$

Therefore, only need to measure the common mode current size on the lead, just can obtain circuit space electromagnetic radiation field strength.

Based on above-mentioned high-frequency circuit electromagnetic radiation diagnosis principle, high-frequency circuit spacing electromagnetic radiation characteristic analyzing and predictor method that the present invention proposes the steps include:

The first step: current probe is linked to each other with the input end of prime amplifier, and the output terminal of prime amplifier is connected to the input end of spectrum analyzer; Current probe is stuck on the cable of circuit loop and measures (as shown in Figure 5), from spectrum analyzer, can read common-mode current value;

According to common-mode current value, calculate the field intensity value of common mode radiation:

$E_{\mathrm{CM}}=1.256\&times;{10}^{-6}\frac{\mathrm{Ifdl}}{r}\sin \mathrm{\&theta;}$

The differential mode probe is linked to each other with the input end of prime amplifier, and the output terminal of prime amplifier is connected to the input end of spectrum analyzer.The differential mode probe card is measured on the cable of circuit loop; From spectrum analyzer, can read the differential-mode current value;

According to the differential-mode current value, calculate the field intensity value of differential mode radiation:

$E_{\mathrm{DM}}=2.632\&times;{10}^{-14}\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{IdS}}{r}$

If the common mode radiation field intensity value that calculates is much larger than differential mode radiation field intensity value, then the electromagnetic interference in circuit-under-test loop is based on common mode radiation; Otherwise, based on the differential mode radiation;

In second step, current probe is stuck on the circuit-under-test ground cable; The ground cable of circuit is divided into plurality of sections, the migration current probe position on ground cable then, measure the current parameters value of each section of ground cable, counting circuit external electromagnetic field field intensity value respectively:

$\left|E_c\right|\&ap;\frac{2\mathrm{\&pi;f}\&times;{10}^{-7}F({\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="H200810242654XE00011.png"\; state="\{\{state\}\}">I</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">I</figure-callout>}}_2+...+I_n)l}{3\sqrt{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="H200810242654XE00011.png,H200810242654XE00031.png"\; state="\{\{state\}\}">r</figure-callout>}}^2+{(H-0.8)}^2}}V/m$

Therefore visible circuit parameter (radio-frequency current or voltage) has corresponding relation with the electromagnetic field parameter, can estimate the size of circuit space radiation field by the metering circuit parameter.

The present invention analyzes and estimates the electromagnetic radiation characteristic of high-frequency circuit by current measurement, can draw: electromagnetic radiation characteristic in (1) circuit, and promptly circuit is main still based on the differential mode radiation with the common mode radiation; (2) the circuit space electromagnetic field is strong and weak relatively.This method is easy, quick, practical.

Description of drawings

Radiation Emission in Fig. 1 high-frequency circuit.What describe among the figure is the Radiation Emission that circuit loop causes equivalent coil antenna, and transmission cable causes the Radiation Emission of the short straight antenna of equivalence.Wherein, the 1st, radiated electric field, the 2nd, radiation field, the 3rd, high-frequency current probe, the 4th, HF voltage probe, the 5th, circuit-under-test.

Fig. 2 common mode radiation model.Picture is described is the electric dipole common mode radiation noise that constitutes mainly due to the short straight antenna of equivalence that non-good earth or ground connection reflection current potential cause.The current potential of signal ground is non-vanishing, makes the electric current return path be affected, and is equivalent to have an electric current to go out from ground current like this, produces the common mode radiation noise then, and the circuit model of this moment is an electric dipole common mode model.Wherein, the 6th, the cable of the short straight antenna of equivalence, current potential and the current potential between the ground of the earth point B of circuit are non-vanishing, i.e. V _BA≠ 0.

Fig. 3 differential mode radiation model.Picture is described is the magnetic dipole differential mode radiated noise that the equivalent loop antenna that do not have the large-signal loop of fine control to cause constitutes.The big loop cabling equivalence of circuit is a coil antenna, and the circuit model of this moment is a magnetic dipole differential mode model.Wherein, 7 is the circuit loop of equivalent coil antenna.

Fig. 4 high-frequency current probe is estimated schematic diagram, just can reach the purpose of being estimated the electromagnetic field parameter by circuit parameter by calculating as long as measure the field intensity size that each section of ground cable give off.Wherein, the electric current I on every section junior unit of circuit cable ₁, I ₂... I _iI _nForming compound in the space is:

$\stackrel{\&RightArrow;}{E}=f\left(I_i\right)=\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{\stackrel{\&RightArrow;}{E}}_i.$

Fig. 5 current probe instrumentation plan.The input end of current probe is stuck on the circuit cable, and output terminal links to each other with the prime amplifier input end, and the output of amplifier connects spectrum analyzer.Wherein spectrum analyzer, prime amplifier and current probe are to mate mutually, and matched impedance is 50 Ω.Wherein, the 3rd, high-frequency current probe, the 8th, circuit loop cable.

Fig. 6 test specimen circuit theory diagrams.Driving voltage is DC 5V in the circuit, and CRY, 74LS04 and 74LS90 are respectively the active crystal oscillator of dual inline type 10MHz, phase inverter and decade adder, and the size of resistance R is 330 Ω.

Fig. 7 high-frequency current probe is to 60cm ²Circuit (high differential mode, S1) and 24cm ²(the common mode differential mode is suitable, S2) measurement result of loop cable for circuit.(a) figure is the measurement result to the S1 circuit, and (b) figure is the measurement result to the S2 circuit.Wherein, the swept frequency range of spectrum analyzer is: 30MHz～500MHz, datum are 90dBuV.

Fig. 8 uses the differential mode probe to 60cm ²Circuit (high differential mode, S1) and 24cm ²(the common mode differential mode is suitable, S2) measurement result of loop cable for circuit.(a) figure is the measurement result to the S1 circuit, and (b) figure is the measurement result to the S2 circuit.Wherein, the swept frequency range of spectrum analyzer is: 30MHz～500MHz, datum is-10dBm.

Fig. 9 electromagnetic field measurements method is to 60cm ²Circuit (high differential mode, S1) and 24cm ²(the common mode differential mode is suitable, electromagnetic field field strength measurement result S2) for circuit.For the validity of circuit parameter method is described, the electromagnetic field measuring method result is compared with circuit parameter method measurement result, wherein, red solid line is represented the measurement result to the S1 circuit, blue dotted line is represented the measurement result to the S2 circuit.That use in the electromagnetic field measuring method is ROHDE﹠amp; The HZ-11 near field probes group that SCHWARZ company produces.

Embodiment

Below in conjunction with embodiment, the inventive method is described in further detail.

In order to say something, checking the inventive method adopts the ten minutes frequency circuit as test specimen to the validity of circuit space electromagnetic radiation characteristic analyzing, and circuit theory diagrams as shown in Figure 6.DC 5V power supply in the circuit provides driving power for the active crystal oscillator of 10MHz, phase inverter 74LS04, decade adder 74LS90, the output terminal of crystal oscillator links to each other with a 74LS04 phase inverter, the 10MHz signal is among phase inverter is input to decade adder 74LS90, make signal frequency become original 1/10th through the division function of 74LS90 digital circuit, be 1MHz, be added to the output resistance two ends of 330 Ω after the shaping of the other 74LS04 phase inverter of last 1MHz signal process.Circuit according to foregoing circuit principle design various wirings mode.S1 represents loop area 60cm ²Circuit, S2 represents loop area 24cm ²Circuit.According to formula (1) (2) as can be known the size of common mode radiation be directly proportional with antenna eliminator length d l, the size of differential mode radiation is directly proportional with loop area dS, so the S1 circuit is differential mode radiation model, the differential mode radiation in the highest flight; S2 compares in the loop S1 and reduces greatly, and its differential mode radiation is effectively suppressed, and common mode radiation and differential mode radiation are also deposited.Use the inventive method that two circuit are measured according to such scheme,

It at first is electromagnetic radiation characteristic in the analysis circuit.Ohm law is converted into logarithmic equation, that is:

|I _CM| _dBuA＝|V _SA| _dBuV-|Z _T| _dBΩ (5)

Wherein: I _CMBe common mode current (dBuA), V _SABe the reading (dBuV) on the spectrum analyzer, Z _TBe matched impedance, because the matched impedance between the surveying instrument is 50 Ω, therefore | Z _T| _{AB Ω}=10lg 50 (dB).From formula (5) as can be seen, as long as guarantee to mate with 50 Ω impedances between the surveying instrument, then common-mode current value is mutual corresponding with reading on the spectrum analyzer.Such as, current probe measurement result shown in Figure 7, S1 circuit spectrum analyzer reading size than S2 circuit approximately little 4～6dB, so the common mode current of S1 circuit also than S2 circuit approximately little 4～6dB.Use and the current probe using method of differential mode probe are similar, and Fig. 8 is the measurement result that differential mode is popped one's head in, the differential-mode current of S1 circuit than S2 circuit big approximately 10dB.So, can obtain in the S1 circuit based on the differential mode radiation, and differential mode radiation and common mode radiation and deposit in the S2 circuit, wherein the differential mode radiation is big slightly.So only needing relatively current probe and the reading size of differential mode probe on spectrum analyzer just can obtain radiation in the circuit fast is main or based on differential mode with the common mode.In fact, known S1 circuit is a differential mode radiation model, and differential mode and common mode and deposit in the S2 circuit are so measurement result is with known consistent.

Next is the strong and weak relatively of electromagnetic field in the estimating circuit.By above-mentioned principle as can be known circuit parameter (radio-frequency current or voltage) and electromagnetic field parameter corresponding relation is arranged, can estimate the size of circuit space radiation field by the metering circuit parameter.In Fig. 7 the common mode current of S1 circuit also than S2 circuit approximately little 4～6dB, can get the common mode radiation of S1 circuit less than the S2 circuit by (4) formula so.For the validity of this scheme is described, use electromagnetic field measuring method that S1 and S2 circuit are measured.That emf probe uses is ROHDE﹠amp; The HZ-11 near field probes group that SCHWARZ company produces, this probe group can be that magnitude of voltage outputs in the middle of the spectrum analyzer its highest frequency 2GHz with electromagnetic field field intensity size conversion.Connect the output terminal of probe and the input end of spectrum analyzer with transmission cable, flyback retrace is come near the space of will popping one's head in circuit, finds out spectrum analyzer output voltage maximal value, and it is stored in the middle of the computing machine.Then according to formula: E _{DB (μ V/m)}=[V _{DB (μ V)}+ AF _{DB (l/m)}] and H _{DB (μ A/m)}=[V _{DB (μ V)}+ AF _{DB (l/m Ω)}] calculate, can obtain S1 and S2 circuit space radiation field field intensity value size respectively.Wherein, E _{DB (μ V/m)}, H _{DB (μ A/m)}Be electric field and magnetic field intensity, V _{DB (μ V)}Be the reading of spectrum analyzer, AF _{DB (l/m)}, AF _{DB (l/m Ω)}Be the antenna factor of electric field probe and magnet field probe, businessman provides by probe.Measurement result as shown in Figure 9.The radiation field of S1 circuit is less than the S2 circuit as seen from the figure, and this measurement result with the high-frequency current probe is consistent.

Claims (1)

1. A high-frequency circuit space electromagnetic radiation characteristic analysis and estimation method, its steps are: Step 1: Connect the current probe to the input terminal of the preamplifier, and connect the output terminal of the preamplifier to the input terminal of the spectrum analyzer; clamp the current probe to the cable of the circuit loop for measurement, and then measure from the spectrum analyzer Can read the common mode current value; According to the common mode current value, calculate the field strength value of the common mode radiation: ${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; CM</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.256</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 6</span>}}\frac{\mathrm{<span\; class="notranslate">\; Ifdl</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$ Among them: I represents the common mode current, f represents the frequency, dl represents the length of the wire; r represents the distance between the cable and the receiving antenna, and θ represents the angle between the electromagnetic field propagation direction and the short straight wire; Connect the differential mode probe to the input of the preamplifier, and the output of the preamplifier to the input of the spectrum analyzer. The differential mode probe is clamped on the cable of the circuit loop for measurement; the differential mode current value can be read from the spectrum analyzer; According to the differential mode current value, calculate the field strength value of the differential mode radiation: ${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; DM</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2.632</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 14</span>}}\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; IdS</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}$ Among them: f represents the frequency, I represents the differential mode current, r represents the distance between the loop and the receiving antenna, and dS represents the loop area; If the calculated common-mode radiation field strength value is much greater than the differential-mode radiation field strength value, the electromagnetic radiation interference of the circuit under test is dominated by common-mode radiation; otherwise, it is dominated by differential-mode radiation; The second step is to clamp the current probe on the ground cable of the circuit under test; divide the ground cable of the circuit into several sections, and then move the position of the current probe on the ground cable to measure the current parameter value of each section of the ground cable , to calculate the field strength value of the electromagnetic field in the circuit space: $<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 7</span>}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.8</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; m</span>}$ Among them: f represents the frequency, F represents the correction factor of the ground reflection in the open field, l represents the length of each small unit, r represents the test distance in the open field, H represents the height of the measuring antenna, I ₁ , I ₂ ... _In represents the circuit line The current on each small unit of the cable.

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