# Patent

## Title
Method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading introduced by software, computer program product for carrying out the method and associated article of manufacture

## Abstract

There is described a method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading. With the method, a designer can, for example, perform a transient simulation on the device only once, and then add frequency spreading with specific parameters by simulation. The resulting frequency spread signal can be observed. The designer can thus evaluate the reduction in electromagnetic emission level, and repeat this process by iteratively applying frequency spreading each time with specific parameters but without having to modify the schematic of the device and to perform another simulation of the device. The method according to this innovation is extremely rapid as the simulation of the design does not need to be repeated at each run of the frequency spreading simulation.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority to International Application No. PCT/IB2014/000370, entitled “METHOD OF OPTIMIZING THE DESIGN OF AN ELECTRONIC DEVICE WITH RESPECT TO ELECTROMAGNETIC EMISSIONS BASED ON FREQUENCY SPREADING INTRODUCED BY SOFTWARE, COMPUTER PROGRAM PRODUCT FOR CARRYING OUT THE METHOD AND ASSOCIATED ARTICLE OF MANUFACTURE,” filed on Feb. 7, 2014, the entirety of which is herein incorporated by reference.
The present application is related to co-pending U.S. patent application Ser. No. 14/324,391, entitled “METHOD OF OPTIMIZING THE DESIGN OF AN ELECTRONIC DEVICE WITH RESPECT TO ELECTROMAGNETIC EMISSIONS BASED ON FREQUENCY SPREADING INTRODUCED BY DATA POST-PROCESSING, COMPUTER PROGRAM PRODUCT FOR CARRYING OUT THE METHOD AND ASSOCIATED ARTICLE OF MANUFACTURE,” filed on Jul. 7, 2014, and U.S. patent application Ser. No. 14/324,404, entitled “METHOD OF OPTIMIZING THE DESIGN OF AN ELECTRONIC DEVICE WITH RESPECT TO ELECTROMAGNETIC EMISSIONS BASED ON FREQUENCY SPREADING INTRODUCED BY HARDWARE, COMPUTER PROGRAM PRODUCT FOR CARRYING OUT THE METHOD AND ASSOCIATED ARTICLE OF MANUFACTURE,” filed on Jul. 7, 2014, the entirety of which are herein incorporated by reference.
FIELD OF THE INVENTION
This invention relates to method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading introduced by software, to a computer program product for carrying out the method and to an associated article of manufacture.
BACKGROUND OF THE INVENTION
Electromagnetic compatibility (EMC) is a fundamental constraint that all electric or electronic equipments must meet to ensure the simultaneous operation of electric or electronic devices present at the same time in a given area, for a given electromagnetic environment.
By definition, EMC covers two complementary aspects: the electromagnetic (EM) emission and the immunity to electromagnetic interferences. When designing new electric or electronic devices, it is desirable to both keep the emission low and ensure robustness of the device, such that it complies with certain limits. Mainly, such EMC limits are defined by standards, e.g. CISPR 25, “Radio disturbance characteristics for the protection of receivers used on board vehicles, boats, and on devices—Limits and methods of measurement”, IEC, 2002. Sometimes, more drastic limits may be defined by the customers. Moreover, the measurement equipment is described in CISPR 16-1-1 Specification for radio disturbance and immunity measuring apparatus and methods—Part 1-1: Radio disturbance and immunity measuring apparatus—Measuring apparatus.
Simulation and measure of EM emissions during the design phase of integrated circuits allows evaluating signals that could cause spurious emissions leading to failure to meet the EMC specifications, before the product is first manufactured. Hence, when EM emission problems are detected by measurements on the manufactured device, the cost of redesign and manufacture may be prohibitive.
Therefore, it has become general practice to evaluate the signals that could cause spurious emissions leading to failure to meet the EMC specifications during the design phase of the device. At this stage it is relatively simple to modify the device to reduce the emission level by modifying the design.
For instance, when the maximum level of EM emissions at a given frequency specified by a standard or by customers is exceeded, the performance can be improved by spreading the signal at a specific frequency over a band of frequencies. Indeed, frequency spreading is often used to reduce the susceptibility of a receiver to an aggressor or to reduce the effect of a transmission on a victim.
The difficulty is to determine the optimum parameters for the frequency spreading, which may include the form of the modulating signal (ramp, triangle, stepped or linear, etc), the frequency of the modulating signal and the peak frequency deviation), without having to spend time simulating “real schematics” or, worse, having to generate numerous versions of the device to test different configurations.
Key principles of frequency spreading applied to EM emission reduction, as well as more general considerations regarding frequency spreading are disclosed in the publication by J. Shepherd, et al, “Getting the most out of frequency spreading”, EMC Compo 2009.
The publication by K. Hörmaier, et al, “An EMI receiver Model to Evaluate Electromagnetic Emissions by Simulation”, IEEE International Instrumentation and Measurement Technology Conference (I2MTC), 2012, discusses various methods of simulating an electromagnetic interference (EMI) test receiver.
Finally, the article by V. Crisafulli, et al, “Model Based Design Tool for EMC Reduction Using Spread Spectrum Techniques in Induction Heating Platform” discusses SPICETM simulation of an equipment. The proposed method applies a previously calculated modulation waveform to the SPICETM schematic of the equipment to be tested. The necessary circuitry for frequency spreading is already included in the SPICETM schematic of the equipment.
However, the addition of the frequency spreading function into the existing schematic of the device under test (DUT) may be difficult to achieve, particularly when various combinations of frequency spreading parameters must be tried.
SUMMARY OF THE INVENTION
The present invention provides a method, a computer program product and an article of manufacture as described in the accompanying claims.
Specific embodiments of the invention are set forth in the dependent claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.



BRIEF DESCRIPTION OF THE DRAWINGS
Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.
FIG. 1A is a schematic block diagram of a setup according to embodiments of the invention when applying frequency spreading to a signal resulting from an electrical simulation of an electronic device.
FIG. 1B is a schematic block diagram of a setup according to embodiments of the invention when applying frequency spreading to a measured signal.
FIG. 2 is a block diagram of a simulation setup for introducing frequency spreading to an existing signal according to a first embodiment.
FIG. 3 is block diagram of a simulation setup for introducing frequency spreading to an existing signal according to a second embodiment.
FIG. 4 is block diagram of a simulation setup for introducing frequency spreading to an existing signal according to a third embodiment.
FIG. 5 is a spectrum diagram showing the spectrum of a frequency spread signal obtained by using the setup of FIG. 4, namely when the frequency spreading is achieved by mixing the existing signal with a frequency spread signal at zero frequency.
FIG. 6 schematically shows an example of an embodiment of a simulation apparatus adapted for carrying out embodiments of the method.
FIG. 7 is a flow diagram illustrating the design flow according to the prior art.
FIG. 8 is a flow diagram illustrating the design flow according to embodiments of the method.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A method of debugging electromagnetic emission problems during the design phase of an electronic device is presented. The device under test (DUT) may be an integrated circuit (IC), a part of an IC like a functional block also named an IP block in the art of electronic circuit design, or a complete system comprising an arrangement of various ICs or a System-on-Chip (SoC).
The device to be designed can be defined using a circuit-level modeling, and thus the simulation of the design can be carried out by means of a conventional circuit simulator.
In further embodiments, however, a high-level behavioral block diagram modeling can be used for defining the electronic device to be designed. Still further, a mixed behavioral and circuit-level description can be used. Accordingly, a block oriented simulator, or a mixed-level behavioral and circuit simulation tool, respectively, can be used for the simulation. These variants allow optimizing the design of the electronic device with respect to electromagnetic emissions before decisions on implementation details at circuit level have to be made.
Embodiments of the invention rely on applying frequency spreading to an existing signal without the need to modify the device or part of the device generating the signal. Frequency spreading is applied in an electrical simulator, by simulating the mixing of the existing signal with a frequency spread signal. Embodiments of the invention can be implemented in any electronic design automation (EDA) or computer-aided design (CAD) tool. The method can be included in the toolbox of any simulator (such as SPICETM, ADSTM (Advanced Design System) available from Agilent, etc.) or mathematical software (such as MatlabTM, for instance). It can be used as part of the design flow.
Because the illustrated embodiments of the present invention may for the most part, be implemented using hardware and/or software components known to those skilled in the art, details will not be explained in any greater extent than that considered necessary, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.
With reference to FIG. 1A, the method of applying frequency spreading may be applied by a frequency spreading simulation setup 100 to a signal resulting from an electrical simulation of the electronic device. The latter electrical simulation may be performed by using another simulation setup 110, adapted to perform an electrical simulation of the electronic device under test. In some embodiments, both setups can share resources, such as components libraries and means of processing data. For example, the frequency spreading simulation setup 100 may be designed as a sub-module of the simulation setup 110 used for simulating the device and generating the signal to be frequency spread.
In a variant illustrated by FIG. 1B, the existing signal to be frequency spread may be a real signal at a pin or terminal of a device measured with a measurement setup 120, for example an oscilloscope.
Data from a transient simulation or from acquisition of a real signal is typically a list of time-voltage pairs (piece-wise linear), which may be stored in a simple data structure like a memory table.
In both cases as illustrated by FIG. 1A and FIG. 1B, namely irrespective of whether data 130 results from electrical simulation by setup 110 or from measurement by setup 120, the frequency spreading is applied by simulating the addition to the existing signal of a frequency spreading signal. The resulting data 130 can be filtered by the frequency spreading simulation setup 100 using various well known methods and the resulting spectrum can be observed. Advantageously, the schematic of the device generating the signal does not need to be modified when testing the reduction of electromagnetic emissions achieved by frequency spreading.
The technical result which is achieved is that reduction in the electromagnetic emissions of an electronic device using frequency spreading can be optimized without the need to modify the device for performing such optimisation. Stated otherwise, embodiments of the invention offer the possibility of trying various frequency spreading parameters by applying frequency spreading to an existing signal generated by the device under test, without modifying the device or part of the device generating the signal for each try.
With reference to FIG. 2, a first embodiment of the frequency spreading setup 100 of FIG. 1A and FIG. 1B is described below. In this embodiment the signal VIN to be frequency spread is added to, namely is mixed with a local oscillator signal VS, which is frequency-spread according to a set of determined frequency spreading parameters.
In the shown example, the signal VIN is multiplied by the signal VS. In this example, indeed, the frequency spreading simulation setup 100 as shown in FIG. 2 is based on the well-known super-heterodyne conversion stage. It may thus comprise an input for receiving the signal VIN to be frequency spread, which is coupled to a first input of a frequency mixer 21, for instance a digital multiplier. The frequency spreading signal VS may be provided by a frequency spread source 20, known as the local oscillator, whose output is coupled to a second input of the multiplier 21. For instance the source 20 may be a memory table storing time-voltage pairs (piece-wise linear). In a variant, the source 20 may be a variable frequency oscillator providing digital output values adapted to be multiplied by multiplier 21 with the data 130 of the signal VIN. The resulting, i.e. mixed signal VMIX output by the multiplier 21 is filtered by a band pass filter 22 to remove all but the desired intermediate frequency (IF) signal. The signal outputted by filter 22 is finally fed to additional circuitry 23 which is adapted to amplify and process the desired signal, and to output the detected signal VMEAS of interest. Signal VMEAS is adapted to be observed by the user to check whether the EMC specifications are met or not.
For mathematical convenience and simplicity of the present description, let us consider that both the existing signal VIN (as defined by data 130) and the frequency spreading signal VS are sine waves. For instance, VIN and VS may be given by:

VIN=EIN×cos(ωt+φ)  (1)

and,

VS=2×cos(ωSt)  (2)

so that the mixed signal VMIX is given by

VMIX=VIN×VS=EIN×cos [(ω±ωS)t+φ]+EIN×cos [(ω−ωS)t+φ]  (3)

These resulting frequency products at the output of the multiplier 21 contain the sum and difference of the two multiplied signals and they are frequency spread with exactly the same parameters as the frequency spread signal VS provided by source 20. Band pass filtering of the product by filter 22 allows one or the other component to be selected before detection.
Examples of implementation as regards the shape of the band pass filter and the detection method can be found in the document CISPR 16-1-1 identified in the introduction of the present description.
With the embodiment as shown in FIG. 2 and discussed above, the sweeping of the desired frequency range can be achieved either by tuning the centre frequency of the band pass filter 22 or by shifting the centre frequency of the frequency spread source 20, or both.
A second embodiment of the setup 100 is shown in FIG. 3, which may use direct quadrature conversion (IQ). This allows avoiding the detection of unwanted products, such as image frequencies, in the output signal VMEAS.
The frequency multiplier 21 and the band-pass filter 22 of FIG. 2 are replaced, on one side, with an in-phase multiplier 31 also named an I-Multiplier and an in-phase filter 33 also named an I-Filter, and, on the other side, with an in-quadrature multiplier 32 also named a Q-Multiplier and an in-quadrature filter 34 also named a Q-Filter. In the implementation as shown, the 90° phase shift required to generate the quadrature signals VS, and VSq fed to the I-Multiplier 31 and the Q-Multiplier 32, respectively, is placed in the frequency spread signal path. Indeed, a 90° phase shifter 30 may be placed between the frequency spread source 20 and the multipliers as shown. In a variant (not shown) the 90° phase shift may alternately be placed in the input signal path. Quadrature conversion ensures correct detection for all cases of phase. In all of these possible implementations, signals VSi and VSq are 90° out of phase with each other.
The filtering of unwanted frequencies by filters 33 and 34 can be achieved with low-pass filtering structures as described, for instance, in the document CISPR 16-1-1 identified in the introduction of the present description.
Detection of the signal VMEAS from the signals VFILi and VFILq output by filters 33 and 34, respectively, may be achieved e.g. by the well-known Sum-of-Squares Detection (SSD) method. To this end, the detector 23 of FIG. 2 is replaced, in the embodiment as shown in FIG. 3, by a Sum-of-Squares detector 35. This detector 35 comprises square operators 37 and 38, following the I-Filter 33 and the Q-Filter 34, respectively. These operators 37 and 38 are adapted to raise the signals VFILi and VFILq output by I-Filter 33 and the Q-Filter 34, respectively, by the exponent of two. The raised signals are then summed by a digital adder 36, which provides the output signal VMEAS to be observed.
Assuming again that both the existing signal VIN (as defined by data 130) and the frequency spreading signal VS are sine waves given above by relations (1) and (2), respectively, we have, for the in-phase path:

VSi=2×cos(ωSt)  (4)

and,

VMIXi=VIN×VSi=EIN×cos [(ω+ωS)t+φ]+EIN×cos [(ω−ωS)t+φ]  (5)

And for the in-quadrature path, we have:

VSq=2×sin(ωSt)  (6)

and,

VMIXq=VIN×VSq=EIN×Sin [(ω+ωS)t+φ]+EIN×Sin [(ω−ωS)t+φ]  (7)

After the filtering by filters 33 and 34, the filtered in-phase and in-quadrature signals VFILi and VFILq, respectively, are given by:

VFILi=EIN×cos [(ω−ωS)t+φ]  (8)

and,

VFILq=EIN×Sin [(ω−ωS)t+φ]  (9)

whereby the output signal VMEAS is given by:

VMEAS=VFILi2+VFILq2=EIN2  (10)

These resulting frequency products at the output of the multipliers 31 and 32 contain the sum and difference of the two multiplied signals and they are frequency spread with exactly the same parameters as the frequency spread signal VS provided by source 20. Low pass filtering of the products by filters 33 and 34 allows the unwanted component to be suppressed before detection.
The frequency spread signal can be generated by any of the classical methods such as those mentioned above. The one with ordinary skills in the art will note that the frequency spreading of the input signal as described in FIG. 2 and FIG. 3 is achieved by adding the signal frequency spread source to the input signal VIN which results from simulation or measurement of the device under test by the first simulation setup 110 or 120, respectively. Therefore, the fundamental and harmonics are spread by the same peak deviation. This means that each harmonic should in principle be studied independently of the others by applying the desired peak frequency deviation to that harmonic, while ignoring the others. However, this can be overcome by indexing the peak deviation proportionally to the frequency being analyzed. Stated otherwise, a peak deviation of the frequency spreading is made proportional to a frequency of the electrical signal being considered with respect to the EMC test.
An alternative to the above feature consists in generating a frequency spread signal centred at zero frequency and mixing it with the existing signal in a quadrature mixer. The output of this mixer is a frequency spread signal at the same frequency as the original signal. The frequency spread signals at zero frequency Vpi and Vpq are generated by phase modulation with the integral of the modulating signal, as will now be explained with reference to FIG. 4.
FIG. 4 shows the schematic of a third embodiment of the frequency spreading simulation setup 100 wherein the input signal VIN is mixed with a frequency spread signal centered at DC, namely at zero frequency, so that the output frequency is the same as the input frequency. In this embodiment, frequency modulation is achieved by phase modulation with the integral of a modulation signal Vmod centered at zero frequency. Further, quadrature processing is used to eliminate the image frequency.
Let us consider that the existing signal VIN (as defined by data 130) is a sine wave given by:

Vin=Ein cos(ωt)  (11)

A 90° phase shifter 40 generates quadrature signals Vini and Vinq which are 90° out of phase with each other, and which are fed to a first input of an I-Multiplier 41 and to a first input of a Q-Multiplier 42, respectively. These quadrature signals are expressed by:

Vini=Ein cos(ωt)

Vinq=Ein sin(ωt)  (12)

In addition, an integrator 45 is adapted to provide the integral Vint of the modulation signal Vmod, such that:

Vint=∫Vmod dt  (13)

Phase modulators 43 and 44 generate an in-phase frequency modulated version Vpi of Vint and an in-quadrature version Vpq of Vint, respectively, such that we have:

Vpi=cos(ΔfVint)

Vpq=sin(ΔfVint)  (14)

where Δf is the is the peak frequency deviation.
Signals Vpi and Vpq are fed to a second input of the I-Multiplier 41 and to a second input of the Q-Multiplier 42, respectively, which generate mixed voltages Vmixi and Vmixq, respectively, where:




  
    
      
        
          
            
              
                
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which shows that the nominal frequency of VS is the same as the frequency of VIN, but that frequency modulation is achieved by phase modulation with the integral of a modulation signal Vmod centered at zero frequency.
To summarize, the modulation signal Vmod is integrated and then it phase modulates the quadrature carriers Vini and Vinq, which are finally added to form the frequency spread signal VS. Although IQ modulation is not necessary, it allows the negative frequencies of the Fourier transform to be used. Setting the carrier frequency to zero allows better use of the Fourier transform.
It will be appreciated by the one with ordinary skills in the art, that although sine waves have been considered for mathematical convenience of the calculations as presented, the methods of frequency spreading according to embodiments as described above can be applied to any waveform.
Also, it will be noted that all the functions required by the methods described above can be formulated in a netlist for an electrical simulator. For example, in a SPICETM (Simulation Program with Integrated Circuit Emphasis) netlist the various mathematical formulas can be implemented in arbitrary voltage generators. The 90° phase shift required in the Q-path can be achieved, for example, with a time delay (equivalent to a quarter of a cycle at the frequency of interest) in a voltage controlled voltage source, for instance. The functions can therefore be conveniently added to the netlist of the circuit being analysed or applied to the signal obtained from a transient simulation of the circuit being analysed (e.g. piece-wise linear data). No specific post-processing with additional software is required.
The spectrum diagram of FIG. 5 illustrates the Fast Fourier transform (FFT) of a frequency spread signal which has been obtained using a frequency spreading simulation setup 100 whose schematic was implemented in CadenceTM and was simulated with MICATM softwares. The frequency spread signal was obtained by using the setup of FIG. 4, namely the frequency spreading was achieved by mixing the existing signal to be analyzed (whose data was contained in an ExcelTM spreadsheet) with a frequency spread signal at zero frequency. It could also have been implemented in a mathematical calculator (such as Matlab, etc) and simulated in any other existing electrical simulator (such as ADS, QUCS, etc.).
A detailed embodiment of an apparatus suitable for carrying out the proposed method will now be described with reference to FIG. 6, in the case of a signal at a given test point of an electronic device (DUT), which is obtained by simulating said device.
Indeed, FIG. 6 describes the general architecture of a simulation apparatus 10 which may embody the invention. The simulation apparatus may be based on the SPICETM suite of software tools, and may be implemented as a programmable apparatus, such as a computer system. In the embodiment as shown, the device to be designed is defined using a circuit-level modeling, and the simulation of the design is carried out by means of a conventional circuit simulator. It will be appreciated by the one with ordinary skills in the art, however, that a high-level behavioral block diagram modeling or a mixed behavioral and circuit-level modeling can be used for defining the electronic device to be designed. In such embodiments (not shown), a block oriented simulator or a mixed-level behavioral and circuit simulation tool, respectively, can be used for the simulation.
The simulation apparatus 10 as shown in FIG. 6 comprises a schematic editor module 11 which is in charge of the edition of the schematic of the electronic device, and which may generate a file of the “.sch” type. The schematic editor may comprise, or is otherwise associated with, a symbol library 12 storing symbols of components used in the circuit design of the electronic device. Thus, the symbol library may be internal or external to the simulation device 10. This database, in one embodiment, may use an object-oriented approach to represent each component in the architecture of an IC, including: Central Processing Unit (CPU), on-chip network buses, functional blocks also referred to as IP (Intellectual property), power supply and ground planes, electrical interconnect (i.e., wiring), and other similar components. Unified schema objects of the database link the components together based on their logical and physical relationships.
Component models, adapted to describe the electrical characteristics and operation of all components of the electronic device, are provided by component libraries 14 of the apparatus. Some or all of these libraries may be external to the device.
The apparatus further comprises a netlist generator module 13, which generates a SPICETM model of the electronic device adapted to serve as input file for a simulator module 15. This netlist file may be of the “.cir” type, that is to say a netlist format compatible with the analog simulation tool WinSPICETM. It contains the netlist description of the electronic device. It may be stored in a SPICETM model storage unit 16, to become available to the simulator module 15.
The simulator module 15 may be a software processing unit configured to execute circuit simulation based on the model of the electronic device. It may be WinSPICETM, for instance. Alternative simulators, based on other component models may also be provided.
At the end of a simulation run, simulation results are made available in the form of a simulation result file, which may be accessed by post-processing tools 17. Different simulation result file formats may be supported by the apparatus. More than one simulation result file may be stored in a simulation result storage unit 18 which, again, may be internal or external to the computer system.
Finally, the simulation apparatus may comprise a Graphical User Interface (GUI) 19, which provides Input/Output functionality using, for example, editing and controlling icons and menus, viewing screens, plot printers, etc.
In particular, the level of EM emissions may be displayed to the user through the interface 19. This allows the user, during the design phase to check the operation of the various functions of the device and, in particular, to evaluate the signals that could cause spurious emissions leading to failure to meet the EMC specifications.
The design flow for optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading will now be described.
The design flow according to the prior art will first be presented with reference to the flow diagram of FIG. 7.
At 71, an initial design of the device is defined. This is performed by the user who, typically, may be an electronic circuit designer.
At 72, there is obtained at least one electrical signal at a given test point of the electronic device. In the shown example, this is achieved by simulating the electronic device, for instance by using the simulation apparatus described above with reference to FIG. 6. In the example as shown, this simulation may be a transient simulation.
At 73, the resulting simulation data can be converted to the frequency domain, for instance using a Fast Fourier transform (FFT) and filtered by various well known methods.
The resulting spectrum is then observed at 74. For example, the level of EM emissions may be displayed to the user through the GUI 19 of the apparatus of FIG. 6, so that the user may visually check whether there is an electromagnetic emission problem or not. For instance, an electromagnetic compatibility (EMC) test may be performed to determine whether the signal being tested does or not cause spurious emissions above a given threshold which would lead to failure to meet the EMC specifications by the actual device.
If not, then the EMC test is passed, and the design of the electronic device is finalized and its layout is computed, at 75. Else, a redesign of the electronic device is performed, in a looped process.
If frequency spreading is not implemented in the actual design of the electronic device, then the user will opt, at 77, to implement frequency spreading in the design as frequency spreading should be investigated as a possible solution. Else, namely when frequency spreading is readily implemented in the design, the user will likely modify the design by choosing new frequency spreading parameters at 78.
Then, the process loops to 72 where another simulation run is performed for the device with an added or newly defined frequency spreading function.
To summarize, having ascertained that the emissions of the device exceed the specified levels at certain frequencies, the designer must choose suitable parameters for the frequency spreading. These parameters include, for instance, the form of the modulating signal (ramp, triangle, stepped or linear, etc), the frequency of the modulating signal and the peak frequency deviation.
The design flow as shown in FIG. 7, however, suffers at least the following drawbacks:

    
    
        on-the-fly modifications to the design must be performed to find the optimum frequency spreading parameters, which modifications are time consuming; and,
        long simulations must be executed after each design modification, since the electronic device simulation performed at 72 lies in the loop of the design flow.
    
    


The design flow according to embodiments of the present invention, allowing to alleviate the above inconvenient, will now be presented with reference to the flow diagram of FIG. 8. This design flow is implemented when it is assumed that no simple design solution can be found to reduce EMC emissions and that frequency spreading should be investigated as a possible solution.
At 81, an initial design of the device is defined. This is similar to the definition of the initial design performed at 71, in the design flow of FIG. 7 as described above.
At 82, there is obtained at least one electrical signal at a given test point of the electronic device. In the shown example, this is achieved by simulating the electronic device, for instance by using the simulation apparatus described above with reference to FIG. 6. In the example as shown, this simulation may be a transient simulation. This, also, is similar to the simulation of the initial design performed at 72, in the design flow of FIG. 7 as described above.
At 83, the resulting simulation data corresponding to this electrical signal is stored, for example in the simulation result storage unit 18 of FIG. 6, for being further processed within the framework of the frequency spreading simulation process.
This further processing of the stored data is then performed, at 84. Said processing comprises applying frequency spreading by mixing, at simulation level, the electrical signal obtained at 82 with a frequency spread signal. In other words, it comprises simulating the mixing of the electrical signal based on the stored data which define said electrical signal, with a frequency spread signal.
At the first iteration of 84, frequency spreading is applied to the electrical signal according to an initial set of frequency spreading parameters, suitable to reduce electromagnetic emissions of the device.
This may be achieved, in one embodiment, by simulating the mixing of said electrical signal with said frequency spread signal in a mixer, as was described above with reference to FIG. 2, for instance.
In another embodiment, mixing the electrical signal with the frequency spread signal at simulation level comprises simulating the mixing of said electrical signal with said frequency spread signal in a quadrature mixer, as was described above with reference to FIG. 3.
In both embodiments, the peak deviation of the frequency spreading may be made proportional to a frequency of the electrical signal which is considered for performing the EMC test (see below). That way, it is not necessary to study each harmonic independently of the others by applying the desired peak frequency deviation to that harmonic while ignoring the others, even though the fundamental and harmonics are spread by the same peak deviation.
In still another embodiment, the mixing of the electrical signal with the frequency spread signal at simulation level comprises simulating the mixing of said electrical signal with said frequency spread signal at zero frequency in a quadrature mixer, as was described above with reference to FIG. 4.
At 85, the resulting simulation data can be converted to the frequency domain, for instance using a FFT, and filtered by various well known methods. This, again, is similar to the conversion and filtering performed at 73 in the design flow of FIG. 7 as described above.
The resulting spectrum is then observed at 86. For example, the level of EM emissions may be displayed to the user through the GUI 19 of the apparatus of FIG. 6, so that the user may visually check whether there is an electromagnetic emission problem or not. In some embodiments a given EMC test is passed when the signal being tested does not cause spurious emissions above a given threshold which would lead to failure to meet the EMC specifications by the actual device.
If the EMC test is passed, then the design of the electronic device is modified at 87 to introduce a frequency spreading feature corresponding to the initial set of frequency spreading parameters.
Else, the steps of applying frequency spreading to the electrical signal and checking whether the frequency spread signal passes the EMC test are repeated, at 84 and 86, respectively, with respect to another set of frequency spreading parameters, different from the initial set of frequency spreading parameters. This set of frequency spreading parameters is selected at 88. Also, the frequency conversion and filtering performed at 85 are repeated. It will be appreciated, however, that the transient simulation which had been performed at 82 is not repeated. Stated otherwise, this simulation is performed only once in the design flow according to embodiments. This yields in a significant reduction in the time needed to optimize the design of the electronic device with respect to electromagnetic emissions using frequency spreading, compared with the prior art.
In some embodiments, the above steps may be repeated until it is determined, at 86, that the EMC test is passed and the process jumps to the design modification at 87. More precisely, repeating the steps 84 of applying frequency spreading to the electrical signal and checking 86 whether the frequency spread signal passes the EMC test may be performed iteratively with respect to other, namely respective sets of frequency spreading parameters, until the EMC test is passed or until an end condition for the iterations is met. Such end condition can be met, for example, when a given number of iterations have been run, or when the reduction in the electromagnetic emissions caused by the frequency spread signal remains below a given threshold thus indicating that no significant improvement can be expected if iterations are continued further.
After the design has been modified at 87 to introduce a frequency spreading feature corresponding to the optimum frequency spreading parameters, another simulation run is launched at 90, to obtain electrical signals which may include at least the electrical signal at the test point previously considered. In the shown example, this simulation is a transient simulation performed by using, for instance, the simulation apparatus as described above with reference to FIG. 6. It will be appreciated that this transient simulation is a relatively long simulation (compared to simulation at 82) since it is a simulation with frequency spreading. This is similar to the further iterations of simulations (namely simulations other than the first one) performed at 72 with reference to FIG. 7, according to the design flow of the prior art. However, it will further be appreciated that, unlike the simulations 72 of FIG. 7 which are iteratively repeated, the relatively long transient simulation 90 of the invention is carried out only once.
At 91, the resulting simulation data can then be converted to the frequency domain, for instance using a Fast Fourier transform (FFT) and filtered by various well known methods so as to filter power out of the frequency band(s) of interest.
The resulting spectrum is then observed at 93. For example, the level of EM emissions may be displayed to the user through the GUI 19 of the apparatus of FIG. 6, so that the user may visually check whether the EMC test is passed. In practice, the test is passed when the signal being tested does not cause spurious emissions above a given threshold which would lead to failure to meet the EMC specifications by the actual device. This may be determined by the user with consideration of the spectrum of the signal thanks to the GUI 19 by any appropriate means.
If the EMC test is passed, then the design of the electronic device is finalized and its layout is computed, at 94. Else, a failure analysis may be performed, at 95, in order to check whether electronic device as redesigned to include the frequency spreading actually generates the expected frequency spreading or not. In cases where there are still EMC problems at that stage, a more in-depth redesign of the electronic device may need to be considered.
Advantages of the solution as described in the above include at least the following:

    
    
        no modifications to the design are required to find the optimum frequency spreading parameters;
        a relatively short transient simulation of the existing design (namely without frequency spreading) only needs to be carried out once at 82;
        the design is modified only once, at 87, when the optimum frequency spreading parameters have been determined; and,
        the relatively long transient simulation of the optimized design (namely with frequency spreading) only needs to be carried out once at 90.
    
    


To summarize, having ascertained, for instance by simulation or by measurements, that the emissions of a device exceed the specified levels at certain frequencies, the designer may decide to explore frequency spreading as a possible solution. What must be done is to choose suitable parameters for the frequency spreading, which are the form of the modulating signal (ramp, triangle, stepped or linear, etc), the frequency of the modulating signal and the peak frequency deviation. At this stage it is relatively simple to modify the device to reduce the emission level by adding frequency spreading.
With the invention the designer can, for example, perform a transient simulation on the device only once, and then simulate mixing of the obtained electrical signal with a frequency spread signal to add frequency spreading with specific parameters at simulation level. The resulting data can be filtered by various methods and the resulting spectrum observed. The designer can thus evaluate the reduction in electromagnetic emission level, and repeat this process by iteratively applying frequency spreading each time with specific parameters but without having to modify the schematic of the device and to perform another simulation of the device.
Thus, the method according to the invention is extremely rapid, as only the same set of signal data defining the electrical signal to be frequency spread is manipulated at each iteration. The frequency spreading parameters can be modified and the simulation of the mixing can be run again. This way, many different configurations of frequency spreading parameters can be tested in a very short time. Therefore, the proposed method is considerably less time consuming than having to re-run transient simulations as is the case when the invention is not implemented and the frequency spreading function is added in the schematic of the device which thus needs to be simulated at each try of a set of frequency spreading parameters.
Indeed, designers are able to optimize frequency spreading parameters rapidly and apply them to the design of the device before the first tape-out, thereby avoiding costly redesign after EMC characterization.
The method according to this innovation is extremely rapid as the simulation of the design does not need to be repeated at each run of the frequency spreading simulation. Only the simulation of the mixing of the existing electrical signal with the frequency spread signal is iteratively repeated.
This method of frequency spreading can be applied to any waveform. If the waveform contains a fundamental frequency and harmonics, the frequency deviation of each harmonic is multiplied by the order of the harmonic, as is the case in frequency spreading implemented in a real device.
The invention may also be implemented in a computer program for running on a computer system, at least including code portions for performing steps of a method according to the invention when run on a programmable apparatus, such as a computer system or enabling a programmable apparatus to perform functions of a device or system according to the invention. The computer program may for instance include one or more of: a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system. The computer program may be provided on a data carrier, such as a CD-rom or diskette, stored with data loadable in a memory of a computer system, the data representing the computer program. The data carrier may further be a data connection, such as a telephone cable or a wireless connection.
In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, the time-value pairs of which the signal data is constituted are not necessarily obtained from an electrical simulation of the device using a simulation apparatus as in the example described above with reference to FIG. 6 to FIG. 8. Indeed, time-value pairs defining the signal data may also be obtained from a time domain measurement. In some embodiment, this may be achieved by measuring a real signal at a test point of a real electronic device, which may be an external pin of the device pin or a terminal of a device measured, e.g., with an oscilloscope.
Some of the above embodiments, as applicable, may be implemented using a variety of different information processing systems. For example, although FIG. 6 and the discussion thereof describe an exemplary simulation architecture, this exemplary architecture is presented merely to provide a useful reference in discussing various aspects of the invention. Of course, the description of the architecture has been simplified for purposes of discussion, and it is just one of many different types of appropriate architectures that may be used in accordance with the invention. Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements.
Furthermore, those skilled in the art will recognize that boundaries between the functionality of the above described operations are merely illustrative. The functionality of multiple operations may be combined into a single operation, and/or the functionality of a single operation may be distributed in additional operations. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.
All or some of the software described herein may be received elements of system 10, for example, from computer readable media or other media on other computer systems. Such computer readable media may be permanently, removably or remotely coupled to an information processing system such as system 10. The computer readable media may include, for example and without limitation, any number of the following: magnetic storage media including disk and tape storage media; optical storage media such as compact disk media (e.g., CD-ROM, CD-R, etc.) and digital video disk storage media; nonvolatile memory storage media including semiconductor-based memory units such as FLASH memory, EEPROM, EPROM, ROM; ferromagnetic digital memories; MRAM; volatile storage media including registers, buffers or caches, main memory, RAM, etc.; and data transmission media including computer networks, point-to-point telecommunication equipment, and carrier wave transmission media, just to name a few.
In one embodiment, system 10 is a computer system such as a personal computer system. Other embodiments may include different types of computer systems. Computer systems are information handling systems which can be designed to give independent computing power to one or more users. Computer systems may be found in many forms including but not limited to mainframes, minicomputers, servers, workstations, personal computers, notepads, personal digital assistants, electronic games, automotive and other embedded systems, cell phones and various other wireless devices. A typical computer system includes at least one processing unit, associated memory and a number of input/output (I/O) devices.
A computer system processes information according to a program and produces resultant output information via I/O devices. A program is a list of instructions such as a particular application program and/or an operating system. A computer program is typically stored internally on computer readable storage medium or transmitted to the computer system via a computer readable transmission medium. A computer process typically includes an executing (running) program or portion of a program, current program values and state information, and the resources used by the operating system to manage the execution of the process. A parent process may spawn other, child processes to help perform the overall functionality of the parent process. Because the parent process specifically spawns the child processes to perform a portion of the overall functionality of the parent process, the functions performed by child processes (and grandchild processes, etc.) may sometimes be described as being performed by the parent process.
Also, the invention is not limited to physical devices or units implemented in non-programmable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code. Furthermore, the devices may be physically distributed over a number of apparatuses, while functionally operating as a single device. For example,
Also, devices functionally forming separate devices may be integrated in a single physical device.
Other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

## Claims

1. A method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading, the method comprising:
defining an initial design of the device;
obtaining at least one electrical signal at a given test point of the device;
applying frequency spreading to the electrical signal according to an initial set of frequency spreading parameters, suitable to reduce electromagnetic emissions of the device, by mixing said electrical signal with a frequency spread signal at simulation level;
checking whether the frequency spread electrical signal passes a given electromagnetic compatibility, EMC, test;
if the EMC test is passed, then modifying the design to introduce a frequency spreading feature with respect to the set of frequency spreading parameters;
else, repeating applying frequency spreading to the electrical signal and checking whether the frequency spread signal passes the EMC test with respect to another set of frequency spreading parameters, different from the initial set of frequency spreading parameters, and modifying the design to introduce a frequency spreading feature with respect to said other set of frequency spreading parameters if the EMC test is passed, wherein the optimizing the design of the electronic device is used to manufacture the electronic device.

2. The method of claim 1, wherein repeating applying frequency spreading to the electrical signal and checking whether the frequency spread signal passes the EMC test is performed iteratively with respect to other, respective sets of frequency spreading parameters until the EMC test is passed or until an end condition of iterations is met.

3. The method of claim 1, wherein the design of the device is defined at circuit level and/or at behavioral block level, and the electrical signal is obtained at the test point by electrical simulation of the device using a conventional circuit simulator, a block oriented simulator, or a mixed-level behavioral and circuit simulation tool.

4. The method of claim 1, wherein the electrical signal is captured at the test point by measurement performed on the device.

5. The method of claim 1, wherein checking whether the frequency spread electrical signal passes the EMC test comprises frequency filtering the frequency spread electrical signal and observing the resulting spectrum of the signal.

6. The method of claim 1, wherein mixing the electrical signal with the frequency spread signal at simulation level comprises simulating the mixing of said electrical signal with said frequency spread signal in a mixer.

7. The method of claim 1, wherein mixing the electrical signal with a frequency spread signal at simulation level comprises simulating the mixing of said electrical signal with said frequency spread signal in a quadrature mixer.

8. The method of claim 7, wherein a peak deviation of the frequency spreading is proportional to a frequency of the electrical signal being considered with respect to the EMC test.

9. The method of claim 1, wherein mixing the electrical signal with the frequency spread signal at simulation level comprises simulating the mixing of said electrical signal with said frequency spread signal at zero frequency in a quadrature mixer.

10. The method of claim 1, wherein the frequency spreading parameters comprise at least one of the form of the frequency spread signal, the frequency of the frequency spread signal and the peak frequency deviation.

11. A computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, cause the processor to carry out the steps of claim 1.

12. An article of manufacture, comprising a machine-readable medium having machine-readable instructions stored thereon that are executable by a processor to carry out the steps of claim 1.