MEASURING APPARATUS AND A MEASURING METHOD OF ELECTROMAGNETIC INTERFERENCE

Abstract

The present invention relates to a measuring apparatus, comprising: an arbitrary waveform generator to generate, and inject to a coupling network, a combination of N test signals; the coupling network to couple the N test signals to an EUT, and the responses thereof and those signals generated by the EUT itself, to a measuring unit; the measuring unit to measure the electrical rn signals provided by the coupling network; and—a processing unit to process the N test signals and the measured electrical signals, to obtain: the electromagnetic signals, noise or EMI generated by the EUT; and—the Z, Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents. The invention also relates to a measuring method adapted to perform method steps with the apparatus of the invention.

Claims

1. A measuring apparatus, comprising: an arbitrary waveform generator of N ports, wherein N is a natural number, configured and arranged to generate a combination of N test signals, one per port, and to inject said generated N test signals to the N ports of a coupling network; said coupling network configured to couple the N test signals from said arbitrary waveform generator to an equipment under test (EUT) having M ports, where M is equal to, lower than or greater than N, and to couple the responses of the EUT to these N test signals and those signals generated by the EUT itself, to a measuring unit; said measuring unit of at least N ports configured and arranged to measure the electrical signals provided by the coupling network; and a processing unit configured and arranged to process said N test signals and said measured electrical signals, to obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

2. The measuring apparatus according to claim 1, wherein said arbitrary waveform generator is configured and arranged to generate said combination of N test signals from discrete sequences of length L with auto-correlation $\mathrm{Rxx}(\mathrm{Rxx}\left(n\right)=\frac{1}{L}{.Math.}_{l=1}^{L}x\left[l\right]{x^{*}\left[l+n\right]}_L,$ where x* represents the complex conjugate and [l+n].sub.L represents a circular shift with a modulus outside the origin lower or equal than 1/√{square root over (L)} for n≠0, and modulus of the cross-correlation Rxy $\left(\mathrm{Rxy}\left(n\right)=\frac{1}{L}{.Math.}_{l=1}^{L}x\left[l\right]{y^{*}\left[l+n\right]}_L\right)$ with a modulus lower or equal than 1/√{square root over (L)}.

3. The measuring apparatus according to claim 1, wherein the measuring unit has N, 2N or 3N ports.

4. The measuring apparatus according to claim 1, wherein the arbitrary waveform generator is configured and arranged to simultaneously generate said combination of N test signals and/or simultaneously inject the generated N test signals to the N ports of the coupling network, and wherein: the measuring unit is configured and arranged to simultaneously measure the electrical signals provided by the coupling network; and said processing unit is configured and arranged to process said N test signals and said measured electrical signals, to simultaneously obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

5. The measuring apparatus according to claim 1, wherein the arbitrary waveform generator is configured and arranged to at least sequentially inject the generated N test signals to the N ports of the coupling network, and wherein: the measuring unit is configured and arranged to sequentially measure the electrical signals provided by the coupling network; and said processing unit is configured and arranged to process said N test signals and said measured electrical signals, to sequentially obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

6. The measuring apparatus according to claim 1, wherein the aforementioned N test signals are tones or chirp signals or modulated signals or pulses or impulses or wideband signals covering a frequency range to be measured.

7. The measuring apparatus according to claim 1, wherein said processing unit comprises a processor to process said received measured electrical signals using correlation techniques with the injected N test signals, to separate data representative of said electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT from data representative of said Z or Y or S parameters of the EUT or of any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

8. The measuring apparatus according to claim 1, wherein the coupling network contains Line Impedance Stabilization Network (LISN) channels configured and arranged: to electrically couple an AC power supply to the ports of the EUT, and to electrically decouple the arbitrary waveform generator and the measuring unit from the AC power supply network.

9. The measuring apparatus according to claim 1, wherein the processing unit is configured to compute a modal decomposition of data representative of the aforementioned measured electrical signals.

10. The measuring apparatus according to claim 1, wherein said processing unit comprises EMC detectors applied directly on modal decomposition data representative of the aforementioned measured electrical signals.

11. The measuring apparatus according to claim 1, wherein the signal generator is configured to generate and inject N test signals with a period smaller than the switching period of the EUT, to characterize the variations along time of the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

12. The measuring apparatus, according to claim 1, wherein said processing unit is configured and arranged to process the N test signals and the measured electrical signals, also to design: a filter to attenuate the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT; and/or a matching network for the optimal transference of the electromagnetic signals generated by the EUT.

13. A measuring method, comprising: a) generating and injecting test signals to at least some of the ports of an EUT; b) receiving electrical signals from said at least some of the ports of the EUT, after said test signals have been injected thereto, c) simultaneously or sequentially measuring on the received electrical signals: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at said at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

14. The measuring method according to claim 13, comprising using a measuring apparatus comprising: an arbitrary waveform generator of N ports, wherein N is a natural number, configured and arranged to generate a combination of N test signals, one per port, and to inject said generated N test signals to the N ports of a coupling network; said coupling network configured to couple the N test signals from said arbitrary waveform generator to an equipment under test (EUT) having M ports, where M is equal to, lower than or greater than N, and to couple the responses of the EUT to these N test signals and those signals generated by the EUT itself, to a measuring unit said measuring unit of at least N ports configured and arranged to measure the electrical signals provided by the coupling network; and a processing unit configured and arranged to process said N test signals and said measured electrical signals, to obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents; to perform the method steps, wherein: said step a) comprises generating, as said test signals, said combination of N test signals by means ofwith said arbitrary waveform generator, and simultaneously or sequentially injecting the same to at least some of the ports of the EUT through said coupling network; said step b) comprises receiving through said coupling network said electrical signals, including said responses of the EUT to the N test signals and said signals generated by the EUT itself; and said step c) comprises: simultaneously or sequentially measuring, with said measuring unit, the electrical signals provided by the coupling network; and processing, with said processing unit, the N test signals and said measured electrical signals, to simultaneously or sequentially obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

15. The measuring method according to claim 13, wherein: in said step b), said receiving step is a measuring step for measuring electrical signals from said at least some of the ports of the EUT, after said test signals have been injected thereto; and in said step c), said simultaneous or sequential measuring step refers to a processing/computing step for simultaneously or sequentially processing/computing from the measured electrical signals: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at said at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

16. The measuring method according to claim 15, comprising using a measuring apparatus comprising: an arbitrary waveform generator of N ports, wherein N is a natural number, configured and arranged to generate a combination of N test signals, one per port, and to inject said generated N test signals to the N ports of a coupling network; said coupling network configured to couple the N test signals from said arbitrary waveform generator to an equipment under test (EUT) having M ports, where M is equal to, lower than or greater than N, and to couple the responses of the EUT to these N test signals and those signals generated by the EUT itself, to a measuring unit said measuring unit of at least N ports configured and arranged to measure the electrical signals provided by the coupling network; and a processing unit configured and arranged to process said N test signals and said measured electrical signals, to obtain: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents. to perform the method steps, wherein: said step a) comprises generating, as said test signals, said combination of N test signals with said arbitrary waveform generator, and simultaneously or sequentially injecting the same to at least some of the ports of the EUT through said coupling network; said step b) comprises simultaneously or sequentially measuring, with said measuring unit, the electrical signals provided by the coupling network, including said responses of the EUT to the N test signals and said signals generated by the EUT itself; and said step c) comprises: processing, with said processing unit, the N test signals and said measured electrical signals, to simultaneously or sequentially compute: the electromagnetic signals or noise or electromagnetic interference (EMI) generated by the EUT at at least some of its ports; and the Z or Y or S parameters of the EUT or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents.

17. The measuring method according to claim 13, comprising: building a circuit model or modal model of the EUT; and designing an optimal power filter or matching network, and/or components thereof, by predicting the levels of electromagnetic signals or noise or EMI generated by the EUT when virtually connect said built circuit and/or modal models to electric filter or matching network components and simulate their operation.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0075] In the following some preferred embodiments of the invention will be described with reference to the enclosed figures. They are provided only for illustration purposes without however limiting the scope of the invention.

[0076] FIG. 1. EUT models, among others, that can be generated using the instrument comprising the measuring apparatus of the first aspect of the present invention: a) a N-port EUT; b) Thevenin equivalent model; c) Norton equivalent model.

[0077] FIG. 2. Block diagram of the measurement instrument/apparatus of the first aspect of the present invention electrically coupled to an EUT and to a power line network, for an embodiment.

[0078] FIG. 3. Block diagram of a model of the measurement instrument of the first aspect of the present invention, for an embodiment.

[0079] FIG. 4. Definition of normalized waves used for the analysis in the frequency domain performed for the model of FIG. 3.

[0080] FIG. 5. Two-port EUT model: The S-parameter matrix S.sub.EUT characterizes the internal impedance of the EUT, and the two voltage sources (V.sub.n1 and V.sub.n2) characterize the conducted emissions generated by the EUT, for an embodiment used for the examples of approaches A and B described below.

[0081] FIG. 6. The S-parameters of the EUT used for the examples of approaches A and B, for the EUT model of FIG. 5.

[0082] FIG. 7. Magnitude of the Spectra of the two noise voltage sources also for the examples of approaches A and B, for the EUT model of FIG. 5. CISPR limits for class A equipment are plotted for comparison purposes.

[0083] FIG. 8. Signals (1) b.sub.2M0 and (2) b.sub.4M0 measured with V.sub.g1 and V.sub.g2 switched off, for the example of approach A.

[0084] FIG. 9. Signals (1) b.sub.2M1 and (2) b.sub.4M1 measured with V.sub.g1 switched on and V.sub.g2 switched off, for the same example of approach A.

[0085] FIG. 10. Signals (1) b.sub.2M2 and (2) b.sub.4M2 measured with V.sub.g1 switched off and V.sub.g2 switched on for the same example of approach A of FIGS. 8 and 9.

[0086] FIG. 11. Comparison of the four original and estimated S parameters of the EUT (S.sub.EUT), for the same example of approach A of FIGS. 8, 9 and 10.

[0087] FIG. 12. Comparison of the original and estimated voltage noise sources V.sub.n1 and V.sub.n2 for the same example of approach A of FIGS. 8 to 11.

[0088] FIG. 13. First samples of the MLS sequence of 32767 chips used in the example of approach B.

[0089] FIG. 14. Comparison results of the b.sub.2M,1 and b.sub.2M,2 matrices obtained with the previous method and the ones obtained with the PN sequences.

[0090] FIG. 15. The comparison between the actual S parameters of the EUT and the estimated ones.

[0091] FIG. 1. Comparison between the interferent sources (V.sub.n1 and V.sub.n2) of the EUT and the estimated ones.

[0092] FIG. 17 shows four different examples of coupling networks of the measuring apparatus of the first aspect of the present invention, for different embodiments, particularly: a) a voltage follower; b) current meter; c) a transformer; d) a directional coupler.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0093] In the present section some working embodiments of the measuring apparatus of the first aspect of the present invention and of the different signals intervening in the operation thereof, will be described with reference to the Figures.

[0094] The description below refers to embodiments of the apparatus/method of the present invention to perform sequential measurements (Approach A) of conducted emissions and impedance and also simultaneous measurements (Approach B) thereof.

Measurement Steps to Perform a Sequential or Simultaneous Measurement of Conducted Emissions and Impedance:

[0095] The embodiments described above for the measuring apparatus of the first aspect of the present invention, allow the computation of the conducted emissions and characterization parameters of an EUT. These can be combined to obtain a generic equivalent Thevenin/Norton model of the EUT. By a generic Thevenin/Norton equivalent it is understood in this document any characterization of an EUT (FIG. 1.a) of the form of y=Ax+y.sub.0, where y is a column vector of electrical magnitudes taken as responses, x is a column vector of electrical magnitudes taken as excitations, the matrix A encapsulates the response of the equipment to these excitations (contains its characterization parameters), and y.sub.0 contains the effect of the conducted emissions. The electrical magnitudes can be any combination of voltages and currents. x, y and y.sub.0 can be understood as containing time or frequency characterizations of electrical magnitudes (if time-domain magnitudes are used, Ax must be understood as a matrix convolution). Therefore, the matrix A can be, among others, any of the commonly used parameters (scattering (S) parameters, impedance parameters (Z), admittance parameters (Y), chain scattering or chain transfer (T) parameters, hybrid (H) parameters, chain (ABCD) parameters, etc.) and the column vector yo could represent series voltage sources, shunt current sources, wave sources, etc. In graphical representations of these parameters, it is common to mix elements from different representations, as in FIG. 1.b, where the series voltage sources would naturally fit in an EUT characterization using a Z parameter matrix, or in FIG. 1.c, where the shunt current sources would naturally fit in a characterization using a Y parameter matrix. Since most matrix characterizations can be transformed one into another, mixed graphical characterizations such as those of FIG. 1.b or FIG. 1.c are also possible. In order to measure an equivalent Thevenin/Norton model of the EUT the instrument simultaneously or sequentially measures the conducted emissions and the characterization parameters of any EUT connected to it, and, with this information, constructs its equivalent model.

[0096] The block diagram of the instrument that can perform these measurements is shown in FIG. 2, according to an embodiment of the measuring apparatus of the first aspect of the present invention. It is designed to measure an EUT of N ports (if the EUT has less than N ports, some of the ports of the EUT would remain unused; if the EUT has more than N ports, some of the ports of the EUT would remain unmeasured; with this understood, in the following, the EUT will be supposed an N-port device, for the here described embodiments). The instrument consists of an N-port Arbitrary Waveform Generator; a k×N-port Measuring Unit, being k usually 1, 2 or 3; N Coupling Networks that inject a signal dependent on the signal generated by the Arbitrary Waveform

[0097] Generator to the ports of the EUT, and inject a signal dependent of the response of EUT to the aforementioned excitations to the kxN ports of the Measuring Unit. The Processing Unit will perform most of the computations specified below. In the particular embodiment shown in FIG. 2, the Coupling Networks include the circuitry typical of a channel of an LISN, since it is intended to characterize the mains or power terminals of the EUT. A different embodiment of the invention designed to characterize other kind of terminals, would not have the Coupling Networks connected to the mains through LISN channels.

[0098] The Arbitrary Waveform Generator and the Measuring Unit can work in a base band configuration or include frequency mixers, upconverters, downconverters, etc. The Measuring Unit contains k×N signal measurement devices, which can be actual or equivalent (a multiplexing schema could be used if needed).

[0099] The Processing Unit can be embedded into the physical instrument or be hosted in an external PC or the Cloud.

[0100] The Coupling Networks can be made in a variety of configurations, none of which refers to a switching matrix. For instance, using power dividers and directional couplers, impedance bridges, circulators, voltage or current probes, etc. This definition means that in such coupling networks all ports are always interconnected (contrary to what can happen in a switching matrix with more inputs than outputs or vice versa, where only those ports placed at the switching position are interconnected).

[0101] In order to demonstrate the feasibility of the instrument, it can be modelled as seen in FIG. 3 and described as follows. In this analysis, 4-port Coupling Networks are supposed, although three-port Coupling Networks would be enough for the analysis performed. In a real implementation, the fourth port could be used, for instance, and with the appropriate Coupling Network, to sense the level of the signals injected by the Arbitrary Waveform Generator. In the following analysis, the Coupling Networks are very general. The analysis is performed in the frequency domain. Since any signal admits either a time-domain or a frequency-domain characterization, the analysis performed is general. For the purpose of the analysis, normalized waves are used, but it is understood that the instrument can measure other kinds of electrical signals (that can be expressed as combinations of normalized waves). For the following analysis, ports 1 of the Coupling Networks have a reference impedance equal to the internal impedance of the corresponding Arbitrary Waveform Generator ports. And ports 2 and 4, have a reference impedance equal to the input impedance of the corresponding Measuring Unit ports (a value of k=2 is supposed, although the analysis could analogously be performed for other values of k). The N signal generators of the block diagram of FIG. 2 can be characterized, without loss of generality, by their open-source voltage V.sub.gi and internal impedance Z.sub.01M.sup.(i), i=1, . . . ,N, and the k N Measuring Unit ports (in FIG. 3, 2N) can be characterized, without loss of generality, by their input impedance Z.sub.02M.sup.(i) and Z.sub.04M.sup.(i), i=1, . . . , N. The Arbitrary Waveform Generator and the Measuring Unit devices are coupled to the EUT ports by means of the N Coupling Networks, characterized again, without loss of generality, by their S-parameter matrix, S.sub.M.sup.(i), i=1, . . . ,N. The following analysis is performed, without loss of generality, under the assumption of two Measuring Unit ports for each EUT port. The analysis could also be performed for an arbitrary number of Measuring Unit devices for each EUT port (k). In particular, the case of k=1 can be easily taken into account in the following equations by equating the relevant S parameters of the relevant S.sub.M.sup.(i) matrix to 0.

[0102] The following analysis has been performed using a very general definition on normalized waves (and, therefore, of S parameters), as seen in FIG. 4. The parameters k and Z.sub.0 used for the definition of a normalized wave are indicated below the port. As can be seen, to simplify the computations, the values on the different parameters Z.sub.0 used at ports 1, 2 and 4 of the N Coupling Networks are equal to the internal impedance of the Arbitrary Waveform Generator and the input impedances of the Measuring Unit ports. The values of k and Z.sub.0 at their port 3 are set to accommodate the desired wave definitions at the port of the EUT.

[0103] Let it be the following column vectors,

[00003]$a_{\mathrm{jM}}=\left[\begin{array}{c}{a}_{\mathrm{jM}}^{\left(1\right)}\\ .Math.\\ a_{\mathrm{jM}}^{\left(N\right)}\end{array}\right]b_{\mathrm{jM}}=\left[\begin{array}{c}{b}_{\mathrm{jM}}^{\left(1\right)}\\ .Math.\\ b_{\mathrm{jM}}^{\left(N\right)}\end{array}\right]a=\left[\begin{array}{c}{a}_1\\ .Math.\\ a_N\end{array}\right]b=\left[\begin{array}{c}{b}_1\\ .Math.\\ b_N\end{array}\right]V_n=\left[\begin{array}{c}{V}_{n1}\\ .Math.\\ V_{\mathrm{nN}}\end{array}\right]V_g=\left[\begin{array}{c}{V}_{g1}\\ .Math.\\ V_{\mathrm{gN}}\end{array}\right],$

with=1, . . . ,4. If the S parameter matrix of the EUT and Coupling Networks are

[00004]$S_{\mathrm{EUT}}=\left[\begin{array}{ccc}{s}_{11}& .Math.& s_{1N}\\ .Math.& \ddots & .Math.\\ s_{N1}& .Math.& s_{\mathrm{NN}}\end{array}\right]\mathrm{and}{S}_M^{\left(i\right)}=\left[\begin{array}{ccc}{s}_{11M}^{\left(i\right)}& .Math.& s_{14M}^{\left(i\right)}\\ .Math.& \ddots & .Math.\\ s_{41M}^{\left(i\right)}& .Math.& s_{44M}^{\left(i\right)}\end{array}\right],$

with i=1, . . . ,N, let it be the diagonal matrices

[00005]$S_{\mathrm{ijM}}=\left[\begin{array}{ccc}{s}_{\mathrm{ijM}}^{\left(1\right)}& & 0\\ & \ddots & \\ 0& & s_{\mathrm{ijM}}^{\left(N\right)}\end{array}\right],$

with i=1, . . . ,4, j=1, . . . ,4. Finally, let it be the diagonal matrices

[00006]$K_{\mathrm{jM}}=\left[\begin{array}{ccc}{k}_{\mathrm{jM}}^{\left(1\right)}& & 0\\ & \ddots & \\ 0& & k_{\mathrm{jM}}^{\left(N\right)}\end{array}\right],$

with j=1, . . . ,4.

[0104] Then,

b=S.sub.EUTa

a.sub.1M=K.sub.1MV.sub.g

a.sub.3M=K.sub.3MV.sub.n+b

b.sub.3M=K.sub.3MV.sub.n+a

b.sub.1M=S.sub.11Ma.sub.1M+S.sub.13Ma.sub.3M

b.sub.3M=S.sub.31Ma.sub.1M+S.sub.33Ma.sub.3M

b.sub.2M=S.sub.21Ma.sub.1M+S.sub.23Ma.sub.3M

b.sub.4M=S.sub.41Ma.sub.1M+S.sub.43Ma.sub.3M

From these equations, it follows that
b.sub.3M=(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31Ma.sub.1M+(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M(I.sub.N−S.sub.EUT)K.sub.3MV.sub.na.sub.3M=S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31Ma.sub.1M+(I.sub.N+S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M)(I.sub.N−S.sub.EUT)K.sub.3MV.sub.n.

[0105] From these, all other waves (and therefore, the voltages and currents) at all the ports of the circuit of FIG. 3 can be easily computed.

[0106] From these equations, several measurement strategies (time-domain, frequency-domain, mixed-domain, or spread-spectrum) can be envisaged.

[0107] For instance, two very basic approaches, which can be enriched at several stages, would be the ones described below.

Approach A:

[0108] Suppose an EUT emitting stationary interference. First, the effect of V.sub.n is measured when V.sub.g=0 (a.sub.1M=0), yielding

b.sub.2M0=S.sub.23Ma.sub.3M=S.sub.23M(I.sub.N+S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M)(I.sub.N−S.sub.EUT)K.sub.3MV.sub.n

b.sub.4M0=S.sub.43Ma.sub.3M=S.sub.43M(I.sub.N+S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M)(I.sub.N−S.sub.EUT)K.sub.3MV.sub.n.

[0109] If then adequately timed (synchronized with the interference or with the 50-Hz mains signal, . . . ) measurements are performed with V.sub.g≠0 (a.sub.1M≠0), the following waves are measured,

b.sub.2M=S.sub.21Ma.sub.1MS.sub.23Ma.sub.3M=(S.sub.21M+S.sub.23MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M+b.sub.2M0

b.sub.4M=S.sub.41Ma.sub.1MS.sub.43Ma.sub.3M=(S.sub.41M+S.sub.43MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M+b.sub.4M0

[0110] If N linearly independent (at all frequencies) (column) vectors a.sub.1M, k=1, . . . , N are generated, and its responses measured, the following excitation and response matrices (made up of column vectors) can be constructed,

A=[a.sub.1M,1 . . . a.sub.1M,N]

B.sub.2=[b.sub.2M,1−b.sub.2M0−b.sub.2M,N . . . b.sub.2M0]

B.sub.4=[b.sub.4M,1−b.sub.4M0−b.sub.4M,N . . . b.sub.4M0],

with

B.sub.2=(S.sub.21m+S.sub.23MS.sub.EUT(I.sub.N+S.sub.33MS.sub.EUT).sup.−1S.sub.31M)A

B.sub.4=(S.sub.41M+S.sub.43MS.sub.EUT(I.sub.N+S.sub.33MS.sub.EUT).sup.−1S.sub.31M)A.

[0111] Since A is invertible, S.sub.EDT can be computed from either expression. For instance,

S.sub.EUT=(I.sub.N+S.sub.23M.sup.−1(B.sub.2A.sup.−1−S.sub.21M)S.sub.31M.sup.−1S.sub.33M).sup.−1(S.sub.23M.sup.−1(B.sub.2A.sup.−1−S.sub.21M)S.sub.31M.sup.−1)   Equation 1

[0112] Once S.sub.EUT is known, V.sub.n can be readily computed.

[0113] Example A: Consider the case of a two-port EUT modelled using the characterization of FIG. 5 (to select one, although any other characterization as described above could be used), that consists of a S-parameter network (S.sub.EUT) that characterizes the internal impedance of the EUT (its characterization parameters), and two noise voltage sources (V.sub.n1 and V.sub.n2) that characterize the interference generated by the EUT. Port 1 of the EUT is the line-ground port, and port 2 the neutral-ground port. The S parameters used in this example (based on actual measurements) are shown in FIG. 6, and the magnitude of the two noise-voltage sources are shown in FIG. 7. Some CISPR limits are also plotted only for comparison purposes.

[0114] The Coupling Networks considered for the instrument feature each a CISPR-16 50Ω//50 μH LISN channel, a limiter attenuator and a directional coupler.

[0115] The Measurement steps for this case are: [0116] a. The EUT of N ports (being N any number) is connected to the instrument and switched on. [0117] b. The instrument measures the signals at port 2 and port 4 of the Coupling Networks with both generators V.sub.g1 and V.sub.g2 switched off. The signals measured are what was defined as b.sub.2M0 and b.sub.4M0. FIG. 8 shows this measurement. [0118] c. The instrument measures the signals at port 2 and 4 with the first Generator switched on (V.sub.g1 in this case), and the second switched off (V.sub.g2 in this case) (an easy schema for generating linearly independent signals). The signal used in this particular example is a signal with a flat spectrum from 9 kHz to 30 MHz, although many other signals could be used instead. The injected signals interact with the EUT and are in part reemitted along with the EUT's emissions generated by V.sub.n1 and V.sub.n2 . These signals arrive to the Measuring Unit through ports 2 and 4 of the Coupling Networks, where they are measured. In this case, the measured signals are shown in FIG. 9. [0119] d. In a fourth step, the instrument measures the signals in port 2 and 4 of the coupling Networks with the second generator switched on (V.sub.g2 in this case), and the first switched off (V.sub.g7 in this case), and a signal with similar spectrum as above, as shown in FIG. 10. [0120] e. Using the measurements done in the previous steps, the S parameters of the EUT, S.sub.EUT, can be computed using Equation 1. In this example, the four S parameters are recovered, as shown in FIG. 11. [0121] f. Having measured the S parameters of the EUT, the noise voltage sources can be obtained using:

V.sub.N=(K.sub.3M(I.sub.N−S.sub.EUT).Math.(I.sub.N+S.sub.EUT.sup.−1(I.sub.N−S.sub.33MS.sub.EUT)S.sub.33M)S.sub.23M).sup.−1b.sub.2M0.   Equation 2 [0122] Applying this equation to our example, the two voltage noise sources are perfectly recovered, as shown in FIG. 12.sub.!Error! No se encuentra el origen de la referencia.

[0123] After these five steps, all the information to construct the Thevenin equivalent model of the EUT has been obtained.

Approach B:

[0124] Now, if the excitation is a spread-spectrum one, with the signal generators generating highly-uncorrelated sequences, all the above measurements could be performed simultaneously. The system would be simultaneously excited by N pseudo-noise (PN) sequences and the response of the EUT recorded. Therefore, by performing N.Math.N correlations of all responses by all PN sequences, response column vectors as those described above would be recovered, one for each exciting sequence (although this kind of measurements, and the associated correlations, are time-domain, as before they are characterized by their frequency-domain counterparts for analysis purposes):

b.sub.2M=(S.sub.21M+S.sub.23MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M+b.sub.2M0

b.sub.4M=(S.sub.41M+S.sub.43MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M+b.sub.4M0

b.sub.2M0=S.sub.23Ma.sub.3M=S.sub.23M(I.sub.N−S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M)I .sub.N−S.sub.EUT)K.sub.3MV.sub.n

b.sub.4M0=S.sub.43Ma.sub.3M=S.sub.43M(I.sub.N−S.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.33M)(I.sub.N−S.sub.EUT)K.sub.3MV.sub.n.

[0125] In this case, due to the spreading effect of the correlation to signals other than the exciting PN sequence, the terms b.sub.2M0 and b.sub.4M0 would have a low value and could generally be ignored.

[0126] Then, the matrices

A=[a.sub.1M,1 . . . a.sub.1M,N]

B.sub.2=[b.sub.2M,1−b.sub.2M0 . . . b.sub.2M,N−b.sub.2M0]≈[b.sub.2M,1 . . . b.sub.2M,N]

B.sub.4=[b.sub.4M,1−b.sub.4M0 . . . b.sub.4M,N−b.sub.4M0]≈[b.sub.4M,1 . . . b.sub.4M,N],

could be constructed (the A matrix is also constructed by appropriately recording the N N correlation of the input PN sequences, and is, basically, a diagonal matrix at each measurement frequency), and the S-parameters matrix of the EUT could be obtained by

S.sub.EUT=(I.sub.N+S.sub.23M.sup.−1(B.sub.2A.sup.−1−S.sub.21M)S.sub.31M.sup.−1S.sub.33M).sup.−1(S.sub.23M.sup.−1(B.sub.2A.sup.−1−S.sub.21M)S.sub.31M.sup.−1)

[0127] Once S.sub.EUT is known, the interference vectors b.sub.2M0 and b.sub.4M0 can be recovered from

b.sub.2M0−b.sub.2m−(S.sub.21M+S.sub.23MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M

b.sub.4M0−b.sub.4m−(S.sub.41m+S.sub.43MS.sub.EUT(I.sub.N−S.sub.33MS.sub.EUT).sup.−1S.sub.31M)a.sub.1M,

this time using the PN excitations and their responses directly to perform the computations. From b.sub.2M0 and b.sub.4M0 the interference vector

V.sub.N=(K.sub.3M(I.sub.N−S.sub.EUT).Math.(i I.sub.N+S.sub.EUT.sup.−1(I.sub.N−S.sub.33MS.sub.EUT)S.sub.33M)S.sub.23M).sup.−1b.sub.2M0,

can be obtained.

[0128] This schema of measurement has been presented only as an example to demonstrate that simultaneous measurements of all the parameters of a (generalized) Thevenin equivalent can be performed. As in the case of the more conventional measurement schemas described above, other measurement steps could be performed to arrive at the same result. For instance, the interference levels might be recovered first, and then the S-parameters of the circuit, or the generators could generate a superposition of PN sequences to achieve code-diversity in the measurements, or the measurement of interferences and S-parameters could be performed sequentially, among others. As before, this basic measurement schema can be enriched with algorithms and techniques which improve the numerical accuracy of the results (interpolations, multiple measurements, . . . ).

[0129] Example B: Consider the case of an EUT modelled using the characterization of FIG. 5, with the S-parameter network (S.sub.EUT) shown in FIG. 6, and the two noise voltage sources (V.sub.n1 and V.sub.n2) shown in FIG. 7.

[0130] Again, all Coupling Networks considered for the instrument feature a CISPR-16 50Ω//50 μH LISN channel, an attenuator (transient limiter) and a directional coupler.

[0131] The Measurement steps for this case are: [0132] a. The EUT of 2 ports is connected to the instrument and switched on. [0133] b. The instrument generates the PN sequences. In this example, a single maximum-length (MLS) sequences of 32767 chips is used in both ports simultaneously, but with a time shift of 16384 samples (to avoid an overlapped interference). The measurement period is of 16384 samples. FIG. 13.sub.!Error! No se encuentra el origen de la referencia. shows its first 200 samples. [0134] c. a.sub.1M, b.sub.2M and b.sub.4M are simultaneously measured. These time-domain signals are correlated with the PN sequences. FIG. 14 shows the results of the b.sub.2M,1 and b.sub.2M,2 column vectors obtained after performing the cross-correlations with the PN sequences described above. A median filter has been used to smooth the effect of the interference. [0135] d. Estimation of the S parameters of the EUT using equation 1. FIG. 15 shows the comparison between the actual S parameters of the EUT and the estimated ones. A median filter has been used to smooth the effect of the interference. [0136] e. Estimation of the interferent sources. FIG. 16 shows the comparison between the interferent sources (V.sub.n1 and V.sub.n2) of the EUT and the estimated ones.

[0137] The two approaches described above are only presented as non-limiting examples of possible measurement strategies. The present invention embraces at least any measurement strategy including the generation and injection of the N test signals described in a previous section of the present document, at least those with the auto-correlation R.sub.XX and cross-correlation R.sub.XY described above.

[0138] Considering the definition given in the previous section of this document for the term Coupling Network, and taking into account the same port numeration shown in FIG. 3, some examples of coupling networks are shown in FIG. 17.

[0139] Specifically, FIG. 17.a) shows a coupling network for a Measuring Unit with a single port (k=1). This coupling network consists of a voltage follower (a voltage follower is a circuit whose output voltage straight away follows the input voltage).

[0140] FIG. 17.b) shows a coupling network fora Measuring Unit with two ports (k=2). In this case, the coupling network is composed of two voltage followers and a small value resistor. It allows the measurement of both the voltage at the port of the EUT (port 4), and of its current from the voltage drop across the resistor.

[0141] FIG. 17.c) shows an example of a coupling network using a transformer. Finally, FIG. 17.d) shows an example of a coupling network using only a directional coupler. In this case, part of the generated signal in the Arbitrary Waveform

[0142] Generator goes to the Measuring Unit (port 2), and part to the EUT (port 3). On the other hand, the reflected signal in the EUT, or its conducted emissions, enter via port 3 and goes to the Measuring Unit via port 4.

[0143] The measuring apparatus of the first aspect of the present invention is more complex and complete than those known in the prior art, with a performance not available by any of them. It not only adds the possibility to simultaneously (or sequentially) measure the Z or Y or S parameters or any other meaningful set of parameters that can be computed from the aforementioned ones or from voltages and currents, and the electromagnetic signals or noise or electromagnetic interference generated by an EUT (or what is the same, its conducted emissions), but it also builds, for some embodiments, the Thevenin or Norton equivalent model and, as a last resort, finds the optimal power-line filter to mitigate the conducted emissions. This apparatus aims to accelerate the design and implementation of electronic EUTs, decreasing their design cost, optimizing its implementation and accelerating their time-to-market.

[0144] A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims. For example, substituting the above described LISNs internal to the Coupling Networks by one or more LISNs external thereto.