JP2003150660A - Design method for electronic appliance provided with clock frequency modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decide design specifications of an optimum clock frequency modulation circuit considering both of clock specifications and an EMI suppression effect amount and to shorten a development period of a device to which the clock frequency modulation circuit is applied by obtaining an estimated value of the EMI suppression effect amount by the clock frequency modulation circuit in an EMI standard adaptability test after the device is completed in a stage of deciding the design specifications of the clock frequency modulation circuit. SOLUTION: The design specifications of the clock frequency modulation circuit satisfying the clock specifications 53 which are electric specifications of clock signals and satisfying an EMI effect target value 58 for which an EMI suppression effect in the EMI standard adaptability test 21 is estimated are decided in SSC specification decision 14. Thus, re-design or the like due to insufficiency of the EMI suppression effect in an EMI evaluation after the device is completed is eliminated and the development period is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of designing an electronic device having a clock frequency modulation circuit, and more particularly to a method of designing a clock frequency modulation circuit in consideration of suppression of electromagnetic interference (hereinafter referred to as EMI).

[0002]

BACKGROUND OF THE INVENTION In electronic equipment, clock signals used in digital circuits can make EMI emissions more pronounced. The spectrum component of EMI radiation caused by this clock signal usually exhibits a peak value at a harmonic of the fundamental frequency of the clock signal. EMI regulations
It specifies the test method and the allowable value for this EMI emission amount, and in principle, it is necessary to respect this regulation for products on the market.

Various methods have been studied in order to respect the regulations on EMI radiation. One of them is widely used for the EMI radiation at the harmonic of the fundamental frequency generated by the clock signal. There is a clock frequency modulation method that can be expected to be effective in the frequency band.

When a clock signal with a constant frequency is used, an impulse-shaped EM as shown in the non-modulation spectrum waveform 101 of FIG.
I spectrum component is generated.

On the other hand, when the clock frequency modulation circuit applies frequency modulation according to the modulation signal 103 as shown in FIG. 11 and the modulation clock signal 104 whose frequency changes with the passage of time is used, as shown in FIG. EM spread in frequency like the spectrum waveform 102 at the time of modulation
It becomes an I spectrum component, and its peak value is reduced as compared with the case where a clock signal having a constant frequency is used.

A conventional design method in the case of applying the above-mentioned clock frequency modulation circuit to the electronic equipment for suppressing EMI will be described with reference to FIG.

Device specification 5 determined in device specification determination 11
The circuit specification 52 is determined in the circuit specification determination 12 on the basis of 1. Therefore, the clock specification 53 such as the clock frequency error and the rise / fall time is determined in the clock specification determination 13.

Next, the SSC specification 54, which is the design specification of the clock frequency modulation circuit, is arbitrarily set to SS within the range that satisfies the clock specification 53 determined in the clock specification determination 13.
Determined by C specification determination 14.

After that, circuit design 15 is carried out, and device manufacturing 1
Does the EMI suppression effect by applying the clock frequency modulation circuit after 6 satisfy the EMI effect target value 58 determined by the EMI effect target value determination 18 from the conventional evaluation data 17 based on the evaluation of the conventional device? An effect confirmation 19 is performed to evaluate whether or not. If the conditions are not satisfied, the process returns to SSC specification determination 14 to determine the clock frequency modulation circuit design specification again. If the conditions are satisfied, the performance is confirmed by checking whether the clock specifications are not adversely affected by the frequency modulation of the clock.
Done in.

If the condition is not satisfied here as well, S
Returning to SC specification determination 14, the design specification of the clock frequency modulation circuit is determined again. If the conditions are satisfied, the evaluation of the EMI of the device is completed and the process moves to the EMI standard conformance test 21.

[0011]

According to the above conventional design method, when the design specification of the clock frequency modulation circuit is determined, only the clock specification is used as a reference, and the clock frequency modulation circuit is arbitrarily selected within the range satisfying this. Design specifications are determined. Therefore, E by the clock frequency modulation circuit
Since the amount of MI suppression effect is not known until the EMI evaluation after the device is completed, if the target effect is not obtained as a result of the evaluation, it will be repeated from the determination of the design specifications of the clock frequency modulation circuit again. It causes delay.

Further, in the above conventional design method, since the design specifications of the clock frequency modulation circuit are arbitrarily determined with respect to the clock specifications, the EMI suppression effect amount by the clock frequency modulation circuit is evaluated after the device is completed. It is necessary to evaluate the clock specifications, which also causes a delay in the device development period.

Therefore, an object of the present invention is to perform clock frequency modulation in an EMI standard conformance test after completion of the device at the stage of determining the design specifications of the clock frequency modulation circuit in the process of designing the clock frequency modulation circuit for the purpose of EMI countermeasures. By determining the estimated value of the EMI suppression effect amount by the circuit, the optimum design specifications of the clock frequency modulation circuit considering both the clock specifications and the EMI suppression effect amount are determined, and the development period of the device to which the clock frequency modulation circuit is applied is determined. It is to shorten.

[0014]

The feature of the present invention is that, in the process of developing an electronic device having a clock frequency modulation circuit, a predetermined electromagnetic interference suppressing effect, preferably an electromagnetic interference suppressing effect satisfying an electromagnetic interference standard conformance test. Is a method of designing an electronic device that determines the design specifications of a clock frequency modulation circuit based on the result of the estimation.

Here, in determining the design specifications of the clock frequency modulation circuit, candidates for the clock signal generator having the clock frequency modulation circuit are extracted, and the electromagnetic interference suppressing effect is estimated from the specifications of the candidate clock signal generator. Then, it is possible to select and use the clock signal generator that satisfies the target effect of the estimated electromagnetic interference suppression effect.

Alternatively, in determining the design specifications of the clock frequency modulation circuit, a temporary design specification of the clock frequency modulation circuit is determined, an electromagnetic interference suppressing effect is estimated from the temporary design specification, and the estimated electromagnetic interference suppressing effect is a target. When the above effect is satisfied, the provisional design specification can be determined as the formal design specification of the clock frequency modulation circuit, and the clock frequency modulation circuit can be designed based on this specification.

The electromagnetic interference suppressing effect can be estimated by calculating the spectrum distribution when the clock signal is frequency-modulated to obtain the theoretical value of the electromagnetic interference suppressing effect.

Further, the electromagnetic interference suppressing effect is estimated by correcting the difference between the theoretical value of the electromagnetic interference suppressing effect and the theoretical value when measured under the resolution band setting condition of the electromagnetic interference standard conformance test. be able to.

The electromagnetic interference suppression effect can be estimated by correcting the difference between the theoretical value of the electromagnetic interference suppression effect and the theoretical value when measured by the detection method of the electromagnetic interference standard conformance test. .

As described above, according to the present invention, E in the EMI standard conformance test is performed at the design stage of the clock frequency modulation circuit.
By estimating the MI suppression effect amount, clock specifications and EM
Since it is possible to select the optimum design specification of the clock frequency modulation circuit in consideration of both the I suppression effect amount, the EMI
There is no need to redesign due to lack of effectiveness in the evaluation, and the evaluation after the device is completed can be simplified and the device development period can be shortened.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, in the process of developing an electronic device having a clock frequency modulation circuit according to the embodiment of the present invention, the device specification determination 11 determines the device specification 51 and the circuit specification determination 12 determines the device. The circuit specification 52 is determined based on the specification 51.

The clock specification determination 13 determines the clock specification 53 based on the circuit specification 52. The EMI effect target value determination 18 determines the EMI effect target value 58 based on the conventional evaluation data 17. The SSC specification determination 14 is based on the clock specification 53 and the EMI effect target value 58.
Determine 4. The circuit design 15 performs a circuit design based on the circuit specifications 52, the clock specifications 53, the SSC specifications 54, and the like, and performs the EMI standard conformance test 21 after the devices are assembled in the device manufacturing 16.

Referring to FIG. 2, details of the SSC specification determination 14 shown in FIG. 1 are shown. In FIG. 2, SSC
The G candidate extraction 31 is a clock signal generator (SSC) having a clock frequency modulation circuit based on the clock specification 53.
G) Extract the candidate 71. The SSCG specification extraction 32 is S
The SSCG specification 72 of the SCG candidate 71 is extracted. EMI
The effect estimation 33 obtains the EMI effect estimated value 73 according to the SSCG specification 72. The estimated effect determination 34 compares the EMI effect estimated value 73 with the EMI effect target value 58, and returns to the SSCG candidate extraction 31 if the conditions are not satisfied. If satisfied, the process proceeds to SSCG selection 35 to select the SSCG candidate 71 and shift to the circuit design 15.

Referring to FIG. 3, details of the EMI effect estimation 33 shown in FIG. 2 are shown. The spectrum distribution calculation 41 calculates the modulation spectrum distribution 81 according to the SSCG specification 72 or according to the SSCG provisional specification 76 of FIG. 4 which will be described later. The EMI effect calculation 42 calculates the EMI effect theoretical value 82 from the modulation spectrum distribution 81. The RBW measurement correction 43 corrects the difference in the measurement data due to the setting of the frequency resolution band (RBW) at the time of EMI measurement with respect to the EMI effect theoretical value 82, and calculates the RWB correction EMI effect 83. The detection method measurement correction 44 corrects the difference in the measurement data due to the difference in the detection method at the time of EMI measurement with respect to the RWB correction EMI effect 83, and calculates the EMI effect estimated value 73.

Next, the operation of the present invention will be described.

In FIG. 1, a device specification determination 11 determines a device specification 51, and a circuit specification determination 12 determines a circuit specification 52 based on the device specification 51. The clock specification decision 13 decides a clock specification 53 which is an electrical specification such as a frequency error of the clock signal, a rise time and a fall time based on the circuit specification 52. The EMI effect target value determination 18 determines the amount of EMI suppression effect (EMI) expected for the clock frequency modulation circuit based on the conventional evaluation data 17 collected in the evaluation of the conventional device.
The effect target value 58) is determined. In SSC specification determination 14, the EMI suppression effect by the clock frequency modulation circuit is estimated while considering the clock specification 53, and the design specification (SSC specification 54) of the clock frequency modulation circuit that satisfies the EMI effect target value 58 is determined. . Circuit design 15
Are circuit specifications 52, clock specifications 53, SSC specifications 54
The circuit is designed based on the above, and after the device is assembled in the device manufacturing 16, the EMI standard conformance test 21 is performed.
Details of the SSC specification determination 14 shown in FIG. 1 will be described with reference to FIG. In FIG. 2, the SSCG candidate extraction 31 extracts an SSCG candidate 71 that meets the conditions from a clock signal generator (SSCG) having a clock frequency modulation circuit commercially available as a general-purpose product in consideration of the clock specification 53.

The SSCG specification extraction 32 is performed by the SSCG candidate 7
Specifications required to estimate the EMI suppression effect from 1 (S
Extract the SCG specification 72). The EMI effect estimation 33 is
The EMI suppression effect by the clock frequency modulation circuit is estimated based on the SSCG specifications 72 and the like to obtain the EMI effect estimated value 73. In the estimated effect determination 34, the EMI effect estimated value 73 is E
It is judged whether or not the MI effect target value 58 is satisfied, and if it is not satisfied, the process returns to the SSCG candidate extraction 31 to extract another SSCG candidate and repeat until the condition is satisfied, and if satisfied, the SSCG candidate 71. Select SSCG 3
The selection is made at 5, and the process proceeds to the circuit design 15.

Details of the EMI effect estimation 33 shown in FIG. 2 will be described with reference to FIG. In FIG. 3, the spectrum distribution calculation 41 calculates a modulation spectrum distribution 81 when the clock frequency is modulated based on the SSCG specification 72 or according to the SSCG provisional specification 76 of FIG. 4 described later. As an example of a method of calculating the modulation spectrum distribution 81, there is a method of using an expression representing a frequency modulation signal having a Bessel function as a coefficient as shown in FIG.

The coefficient Jn (Δf / f) of each term using the maximum frequency deviation Δf and the modulation signal frequency fm of this equation as parameters.
m) {n = 0, 1, 2, ...} Indicates the value of each sideband of the spectrum distribution at the time of modulation with respect to the peak value “1” of the spectrum distribution at the time of non-modulation. As a result, the spectrum distribution is obtained as shown in FIG. EM
In the I effect calculation 42, the theoretical EMI effect value 82 is calculated from the difference between the modulation spectrum distribution 81 and the non-modulation spectrum distribution when the clock frequency is not modulated.

The RBW measurement correction 43 is a frequency resolution band (RB) for EMI measurement with respect to the theoretical EMI effect value 82.
WWB is corrected by correcting the difference of the measured data according to the setting value.
The corrected EMI effect 83 is calculated. EMI effect theoretical value 82
The reason why correction is required according to the set value of RBW is
When measuring the harmonic spectrum distribution when the clock frequency is modulated, the measured value when the resolution band RBW of the measuring instrument is narrower than the modulation signal frequency fm of the clock frequency modulation circuit is almost the same as the theoretical value, RBW is fm
When set to a wider band, the measured value is different from the theoretical value.

In the EMI standard conformance test, RBW is 120k
Since the fm of a general clock frequency modulation circuit and SSCG is several tens of kHz, it is usually RB.
It is measured with W set to a wider band than fm. Therefore, as for the EMI suppression effect, when measured under the RBW setting condition in the EMI standard conformance test, the measured value is different from the theoretical value, so it is necessary to prepare and correct the correction data.

As an example of the correction method performed here, there is a method using the correction graph shown in FIG. The graph in FIG. 7 shows the RBW of the measuring instrument as the EMI standard conformance test condition 1
The value of the EMI suppressing effect with respect to the modulation signal frequency fm is measured in the state of being set to 20 kHz, and the difference from the theoretical value of the EMI suppressing effect is represented.

The value for the modulation signal frequency fm used is read from this graph, and the value obtained by subtracting the value from the theoretical value EMI effect 82 is the RBW correction EMI effect 83. The detection method measurement correction 44 is the RWB correction EMI effect 8
For 3, the difference in the measurement data generated due to the difference in the detection method during the EMI measurement is corrected, and the EMI effect estimated value 73 is calculated. The reason why the RWB correction EMI effect 83 needs to be corrected by the detection method is that the theoretical value requires the peak value of the spectrum distribution, whereas the measurement value in the EMI standard conformance test is slightly lower than the peak value. This is because the QP detection method (quasi-peak value detection method) for measuring is used.

Therefore, the EMI suppression effect is also E
Since the detection method in the MI standard conformance test has a value different from the theoretical value, it is necessary to prepare and correct the correction data. An example of the correction method performed here is to use the correction graph shown in FIG.

The graph of FIG. 8 shows the difference between the EMI suppressing effect on the modulation factor of the clock frequency measured by the peak value (theoretical value) of the spectrum distribution and the QP detection method. The value for the modulation factor used is read from this graph, and the value added to the RWB correction EMI effect 83 is the EMI effect estimated value 73.

As another embodiment of the present invention, another detailed configuration and operation of the SSC specification determination 14 shown in FIG. 1 will be described with reference to FIG.
Shown in.

In FIG. 4, the SSCG specification provisional decision 36 is made.
Determines the SSCG temporary specification 76 in consideration of the clock specification 53. EMI effect estimation 33 is based on SSCG provisional specification 76
Based on the above, the EMI suppression effect by the clock frequency modulation circuit is estimated and the EMI effect estimated value 73 is obtained.

The estimated effect judgment 34 is the EMI effect estimated value 7
3 determines whether the EMI effect target value 58 is satisfied, and if not satisfied, the SSCG specification provisional decision 36
Return to and repeat other SSCG tentative specifications until the conditions are satisfied.
The SCG specification decision 37 decides on the SSCG specification 77.
The SSCG circuit design 38 is S based on the SSCG specification 77.
After designing the SSCG circuit in the SCG circuit design 38, the process proceeds to the circuit design 15.

[0040]

According to the present invention, the amount of EMI suppression effect when the clock frequency modulation circuit is applied can be estimated at the design stage.
It is possible to shorten the device development period by eliminating the situation that the shortage of the I suppression effect amount is discovered and the design is restarted.

Further, since the design specifications of the clock frequency modulation circuit can be determined while estimating the EMI suppression effect, the margin for the circuit specifications can be sufficiently taken into consideration during the design stage, so that the performance evaluation of the circuit specifications after the device is completed can be performed. Since it can be simplified, the device development period can be shortened.

[Brief description of drawings]

FIG. 1 is a flow chart showing a development flow of an electronic device apparatus having a clock frequency modulation circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a part of a development flow (clock frequency modulation circuit specification determination flow) of the electronic device apparatus having the clock frequency modulation circuit according to the embodiment of the present invention.

FIG. 3 is a part of a development flow (EM) of an electronic device having a clock frequency modulation circuit according to an embodiment of the present invention.
It is a flowchart showing (I effect estimation flow).

FIG. 4 is a flowchart showing a part of a development flow (clock frequency modulation circuit specification determination flow) of an electronic device apparatus having a clock frequency modulation circuit according to another embodiment of the present invention.

FIG. 5 is an arithmetic expression showing an example of a frequency-modulated spectrum distribution calculation expression.

FIG. 6 is a diagram showing an example of a spectrum distribution obtained by a spectrum distribution calculation formula.

FIG. 7 is a graph showing an example of an EMI suppression effect correction value under a resolution band setting condition in an EMI standard conformance test.

FIG. 8: EM in detection method in EMI standard conformance test
It is a graph which shows an example of an I suppression effect correction value.

FIG. 9 is a flowchart showing a development flow of an electronic device apparatus having a conventional clock frequency modulation circuit.

FIG. 10 is a diagram showing an example of spectrum waveforms at the time of non-modulation and at the time of modulation.

FIG. 11 is a diagram showing an example of a modulation signal and a modulation clock signal in a clock frequency modulation circuit.

[Explanation of symbols]

11 Device specification decision 12 Circuit specification decision 13 Clock specification decision 14 SSC specification decision 15 Circuit design 16 Equipment manufacturing 17 Conventional evaluation data 18 EMI effect target value determination 19 Effect confirmation 20 Performance check 21 EMI standard conformance test 31 SSCG candidate extraction 32 SSCG specification extraction 33 EMI effect estimation 34 Estimated effect judgment 35 SSCG selection 36 SSCG specifications provisional decision 37 SSCG specification decision 38 SSCG circuit design 41 Calculation of spectrum distribution 42 EMI effect calculation 43 RBW measurement correction 44 Detection method measurement correction 51 Device specifications 52 Circuit specifications 53 clock specifications 54 SSC specifications 58 EMI effect target value 71 SSCG candidates 72 SSCG specifications 73 EMI effect estimated value 76 SSCG provisional specifications 77 SSCG specifications 81 Modulation spectrum distribution 82 EMI effect theoretical value 83 RBW correction EMI effect 101 Spectrum waveform without modulation 102 Spectrum waveform during modulation 103 modulated signal 104 modulated clock signal

Claims (7)

[Claims] 1. An electronic device, characterized in that, in a process of developing an electronic device having a clock frequency modulation circuit, a design specification of the clock frequency modulation circuit is determined based on a result of estimating a predetermined electromagnetic interference suppressing effect. Design method. 2. The method of designing an electronic device according to claim 1, wherein the predetermined electromagnetic interference suppressing effect is an electromagnetic interference suppressing effect satisfying an electromagnetic interference standard conformance test. 3. In determining the design specifications of the clock frequency modulation circuit, a candidate of a clock signal generator having a clock frequency modulation circuit is extracted, and the electromagnetic interference suppressing effect is estimated from the specifications of the candidate clock signal generator. 2. The method of designing an electronic device according to claim 1, further comprising selecting and using a clock signal generator whose estimated electromagnetic interference suppression effect satisfies a target effect. 4. In determining the design specifications of the clock frequency modulation circuit, a temporary design specification of the clock frequency modulation circuit is determined, an electromagnetic interference suppressing effect is estimated from the temporary design specification, and the estimated electromagnetic interference suppressing effect is a target. The design of electronic equipment according to claim 1, wherein the provisional design specification is determined as a formal design specification of the clock frequency modulation circuit when the effect is satisfied, and the clock frequency modulation circuit is designed based on this specification. Method. 5. The electronic device according to claim 1, wherein the electromagnetic interference suppressing effect is estimated by calculating a spectrum distribution when a clock signal is frequency-modulated to obtain a theoretical value of the electromagnetic interference suppressing effect. Design method. 6. The electromagnetic interference suppression effect is estimated by correcting the difference between the theoretical value of the electromagnetic interference suppression effect and the theoretical value when measured under the resolution band setting condition of the electromagnetic interference standard conformance test. The method of designing an electronic device according to claim 1, wherein: 7. The electromagnetic interference suppression effect is estimated by correcting the difference between the theoretical value of the electromagnetic interference suppression effect and the theoretical value when measured by a detection method of an electromagnetic interference standard conformance test. The method for designing an electronic device according to claim 1.