JP3916856B2 - Noise generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for quickly generating a noise signal having a desired characteristic and enabling the characteristics of the generated signal to be confirmed in advance.
[0002]
[Prior art]
For example, in a system that communicates digital signals, there is a problem of deterioration in communication quality due to digital signal phase fluctuations (jitter or wander).
[0003]
For this reason, conventionally, the tolerance to the phase fluctuation of the digital signal of the communication system or the equipment constituting the system is measured.
[0004]
In order to perform such measurement in a state close to the actual operating state, conventionally, the clock signal is phase-modulated with the noise signal output from the noise generator, and the digital signal synchronized with this clock signal is transmitted as the communication to be measured. Input to a system or device and measure a code error rate of the communication system or device.
[0005]
In recent years, a digital type is used instead of an analog type as a noise generating device used for such a purpose.
[0006]
Conventionally, as a digital noise generation device, a configuration in which waveform data of a noise signal stored in a memory is read out and output in advance, or exclusive OR of a predetermined stage output of a multistage shift register is used as the first stage. There is a configuration in which outputs of a plurality of pseudo-random generators that generate pseudo-random signals by feeding back to are combined and output.
[0007]
However, in the configuration that reads and outputs the waveform data of the noise signal stored in the memory, the maximum period of the waveform depends on the memory capacity, and the low frequency component of the noise signal that can be output is limited by the memory capacity. For example, in order to generate a phase fluctuation (wander) of 10 Hz or less, a huge amount of memory is required.
[0008]
In addition, in the case of synthesizing pseudo random signals output from multiple pseudo random signal generators, noise signals with low frequency components can be generated by increasing the number of stages of each pseudo random signal generator. However, only noise having characteristics approximating to white noise whose amplitude follows a Gaussian distribution can be generated, and a desired phase fluctuation characteristic cannot be given.
[0009]
In order to solve this, as shown in FIG. 10, the white noise signal output from the noise generator 11 is input to the digital filter 12, and the filter coefficient of the digital filter 12 is variable by the filter coefficient setting means 13. It is conceivable to control and output a noise signal having an arbitrary frequency characteristic from the digital filter 12.
[0010]
The digital filter 12 generally stores the input signal while sequentially shifting it to a plurality of internal storage elements, and performs a product-sum operation between the contents of each storage element and the filter coefficient corresponding to each storage element. The calculation result is sequentially output, and the frequency characteristic of the filter can be varied by varying the filter coefficient.
[0011]
[Problems to be solved by the invention]
However, in order for the digital filter 12 to have an arbitrary frequency characteristic, it is necessary to increase the frequency resolution that can be set. For this purpose, the order of the filter is increased, that is, the number of storage elements in the digital filter is increased. Must.
[0012]
However, when the number of storage elements in the digital filter is increased in this way, there is a problem that it takes a very long time until a noise signal having a desired characteristic is output at the initial stage of operation or when switching characteristics.
[0013]
For example, at the initial stage of operation, the stored value of each storage element in the digital filter 12 is reset to 0, and until the noise signal is input by the number of these storage elements, the digital filter 12 has a desired characteristic. Noise signals having completely different characteristics are output, and if the number of internal storage elements is large as described above, this waiting time becomes very long.
[0014]
On the other hand, when the characteristics of the noise signal to be output can be arbitrarily varied in this way, the noise signal actually output from the noise generation device, or the device that generates jitter and wander using this noise generation device is actually It is inconvenient if the characteristics of the generated clock signal cannot be confirmed.
[0015]
In order to solve this, it is conceivable to measure the characteristics of the noise signal output from the digital filter 12 and the clock signal generated based on the noise signal, and display the measurement result. In the method of actually measuring a noise signal or a clock signal, the configuration of the noise generator and the jitter / wander generator using the noise generator becomes complicated, and depending on the characteristics of the characteristics to be measured, it takes a very long time to complete the measurement ( Several hours to several tens of days), which is difficult to realize.
[0016]
An object of the present invention is to provide a noise generator that solves such problems.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a noise generator according to claim 1 of the present invention comprises:
White noise generating means for generating a digital white noise signal;
A digital signal is stored while being sequentially shifted to a plurality of internal storage elements, and a product-sum operation is performed on the storage contents of the plurality of storage elements, and the noise signal output from the white noise generating means is A filter unit that converts and outputs a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient;
Characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit;
A noise signal sequence equivalent to the storage content of each storage element of the digital filter in a state where a noise signal having a frequency characteristic corresponding to the characteristic coefficient is output from the filter unit, at least at the initial operation of the device, Initial setting means for initial setting in each memory element.
[0018]
The noise generator of claim 2 of the present invention is:
White noise generating means for generating a digital white noise signal;
A digital signal is stored while being sequentially shifted to a plurality of internal storage elements, and a product-sum operation is performed on the storage contents of the plurality of storage elements, and the noise signal output from the white noise generating means is A filter unit that converts and outputs a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient;
Characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit;
A multiplier for multiplying a noise signal output from the filter unit by a preset amplitude coefficient;
Amplitude setting means for setting an arbitrary amplitude coefficient in the multiplier;
Based on the characteristic coefficient set in the filter unit from the characteristic coefficient setting means and the amplitude coefficient of the amplitude setting means, characteristic calculation means for obtaining the characteristic of the noise signal output from the multiplier,
Characteristic display means for displaying the characteristic of the noise signal obtained by the characteristic calculation means.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a noise generator 20 to which the present invention is applied.
[0020]
The white noise generating means 21 of the noise generating device 20 outputs a digital white noise signal n (k) at a predetermined rate. For example, as shown in FIG. 2, the white noise generating means 21 is serially output in synchronization with the clock signal CKn from a plurality of N (for example, N = 12) pseudo random signal generators 22 (1) to 22 (N). Each K-bit random signal is added by an adder circuit 24 and K + [log₂N] white noise signal n (k) is output in bits. Here, the above bracket sign [] represents an integer value obtained by rounding up a decimal number.
[0021]
The plural N pseudo random signal generators 22 (1) to 22 (N) are provided with a code period (2) generated from the same S-stage shift register.^S-1) is generated so that the phase of the output code is greatly different by the control circuit 23 so that the correlation peak of the output is separated, and n (1), n ( 2), ..., n (2^S-2), n (2^SThe noise signal up to -1) is set as one period, and this is repeatedly output.
[0022]
Thus, the instantaneous value of the white noise signal generated by adding a plurality of pseudo-random signals approximates the Gaussian distribution characteristic.
[0023]
The control circuit 23 receives a noise signal output instruction from the initial setting means 31 to be described later, initializes the pseudo random signal generators 22 (1) to 22 (N), and outputs the clock signal CKn.
[0024]
The noise signal n (k) output from the white noise generating unit 21 is input to the filter unit 25. The filter unit 25 has a digital filter that stores a digital signal sequence while sequentially shifting it to a plurality of internal storage elements, and that performs a product-sum operation on the storage contents of the plurality of storage elements. The noise signal n (k) output from 21 is converted into a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient and output.
[0025]
Here, for example, a case where the filter unit 25 is configured by an FIR type digital filter 26 as shown in FIG. 3 will be described.
[0026]
The digital filter 26 includes a plurality of M-stage serial storage elements (also referred to as delay elements) 27 (1) to 27 (M) that store input data while sequentially shifting to the subsequent stage, and a first-stage storage element 27 (1). Filter coefficient (characteristic coefficient of this embodiment) h for input data and output data of each storage element 27 (1) to 27 (M)₀~ H_MAre respectively constituted by multipliers 28 (1) to 28 (M + 1), and an adder 29 for calculating the sum of the outputs of the multipliers 28 (1) to 28 (M + 1).
[0027]
Each storage element 27 (1) to 27 (M) sequentially shifts the noise signal n (k) in synchronization with the clock signal CKn. In addition, each of the storage elements 27 (1) to 27 (M) can set arbitrary values D (1) to D (M) from an initial setting means 31 described later.
[0028]
Further, the filter coefficient h input to the multipliers 28 (1) to 28 (M + 1).₀~ H_MIs set by the characteristic coefficient setting means 30 described later.
[0029]
The FIR type digital filter 26 configured as described above converts the input noise signal n (k) into a filter coefficient h.₀~ H_MIs converted into a noise signal having a frequency characteristic corresponding to the output.
[0030]
The characteristic coefficient setting means 30 is a characteristic coefficient for determining the characteristic of the noise signal u (k) output from the filter unit 25 (when the filter unit 25 is composed of only the digital filter 26 as described above). The filter coefficient is set, and an arbitrary characteristic coefficient can be set by operating an operation unit (not shown).
[0031]
The initial setting means 31 has a memory (ROM) 31a, and noise equivalent to the stored contents of each storage element in the digital filter in a state where a noise signal having a frequency characteristic corresponding to the characteristic coefficient is output from the filter unit 25. A signal string is obtained based on the contents of the memory 31a, and is initially set in each storage element in the digital filter at least at the initial operation of the apparatus.
[0032]
That is, when the filter unit 25 is constituted only by the digital filter 26 as described above, the filter coefficient h is changed from the digital filter 26 to the filter coefficient h.₀~ H_MA noise signal sequence equivalent to the stored contents of the storage elements 27 (1) to 27 (M) in a state where a noise signal having a frequency characteristic corresponding to is output is initialized.
[0033]
Here, if the noise signal n (1) generated at the initial stage of operation by the white noise generating means 21 is known, M noise signals n (2) before the noise signal n (1) are known.^N-1), n (2^N-2), ..., n (2^N-M) is stored in advance in the memory 31a as initial values D (1) to D (M), respectively, and at the initial stage of operation such as power-on, as shown in FIG. 1) to 27 (M) are respectively initialized, and then the white noise generating means 21 is instructed to output a noise signal.
[0034]
For this reason, since the internal state of the filter unit 25 is immediately set to the same state as the steady state at the initial stage of operation, the filter unit 25 sets the filter coefficient h set by the characteristic coefficient setting unit 30.₀~ H_MA noise signal having a frequency characteristic corresponding to is immediately output.
[0035]
The noise signal u (k) output from the filter unit 25 is input to the multiplier 32. The multiplier 32 multiplies the noise signal u (k) by the amplitude coefficient A set by the amplitude setting means 33 and outputs the multiplication result as a noise signal y (k) having a desired characteristic.
[0036]
Further, the characteristic calculation unit 34 determines the frequency characteristic of the noise signal y (k) output from the multiplier 32 based on the characteristic coefficient set in the filter unit 25 and the amplitude coefficient A set in the multiplier 32. Find the amplitude.
[0037]
The characteristic display means 35 displays the characteristic of the noise signal obtained by the characteristic calculation means 34 on the display 36 as a graph or a numerical value.
[0038]
In the noise generator 20 configured as described above, each storage element 27 (1) in the digital filter 26 in a state where a noise signal having a frequency characteristic corresponding to the characteristic coefficient is output from the filter unit 25 by the initial setting means 31. A noise signal equivalent to the stored content of .about.27 (M) is initially set in each of the storage elements 27 (1) to 27 (M) at least at the initial operation of the apparatus.
[0039]
Therefore, it is possible to immediately output a noise signal having a frequency characteristic corresponding to the characteristic coefficient from the filter unit 25 without waiting for the M noise signals from the white noise generating unit 21 to be taken into the filter unit 25. It is possible to eliminate the influence of measurement or the like due to the output of a noise signal that does not match the characteristics.
[0040]
Further, the characteristic calculation means 34 obtains the characteristic of the output noise signal y (k) based on the characteristic coefficient set in the filter unit 25 from the characteristic coefficient setting means 30 and the amplitude coefficient A of the amplitude setting means 33, Since the characteristic is displayed by the characteristic display means 35, the characteristic of the output noise signal y (k) can be confirmed in advance and quickly, which is convenient.
[0041]
In the above description, the case where the filter unit 25 includes only the digital filter 26 has been described. However, this does not limit the present invention.
[0042]
For example, as shown in FIG. 5, the filter unit 25 can be configured by a branching circuit 41, a weighting circuit 43, and a synthesis circuit 45 including a digital filter.
[0043]
The demultiplexing circuit 41 is configured by cascading a plurality of P ½ decimating circuits 42 (1) to 42 (P).
[0044]
Each of the ½ decimating circuits 42 (1) to 42 (P) is a circuit that alternately distributes input data to two output paths and outputs the data at a rate ½ of the input rate.
[0045]
When the noise signal n (1), n (2), n (3),... Of FIG. 6A is input, the 1/2 decimating circuit 42 (P) of the first stage receives from one of the output terminals. 6B, odd-numbered noise signals n (1), n (3), n (5),... Are output, and the even-numbered noise signal n (2) is output from the other output terminal. , N (4), n (6),. The noise signal output from the other output terminal is input to the second-stage 1/2 decimating circuit 42 (P-1).
[0046]
Similarly, the second-stage ½ decimating circuit 42 (P-1) is connected to one of the input noise signals n (2), n (4), n (6),. As shown in (c), noise signals n (2), n (6), n (10),... Are output, and the noise signals n (4), n (8), n (12) are output from the other output terminal. ), ... are output. The noise signal output from the other output terminal is input to the third-stage 1/2 decimating circuit 42 (P-2).
[0047]
Similarly, from one output terminal of the third stage decimating circuit 42 (P-2), as shown in FIG. 6D, noise signals n (4), n (12), n ( 20),... Are output, and noise signals n (8), n (16), n (24),... Are output from the other output terminal, and the fourth-stage 1/2 decimating circuit 42 (P-3) is output. ), Noise signals n (8), n (24), n (40),... Are output from the other output terminal, as shown in FIG. (16), n (32), n (56),... Are output, and the output rate is lowered by 1/2 from each 1/2 decimating circuit 42 (P-4) to 42 (1). A noise signal is output.
[0048]
Thus, the noise signal n output at a different rate from one output terminal of each of the ½ decimating circuits 42 (1) to 42 (P).₁, N₂, N₃..., n_{P + 1}Are respectively input to the multipliers 44 (1) to 44 (P + 1) of the weighting circuit 43.
[0049]
The multipliers 44 (1) to 44 (P + 1) receive the input noise signal n.₁, N₂, N₃..., n_{P + 1}, Weighting coefficient (characteristic coefficient) σ₁, Σ₂, Σ₃…, Σ_{P + 1}Multiply and output.
[0050]
Thus, the noise signal n at each rate₁, N₂, N₃..., n_{P + 1}Is weighted, the frequency characteristic of the noise signal u (k) output from the filter unit 25 can be arbitrarily set.
[0051]
For example, by performing weighting as shown in FIG. 7 (P is 12 in this figure), a clock signal having a phase fluctuation of a power spectrum density distribution corresponding to a specific TDEV mask characteristic used for wander evaluation is generated. Can do. At this time, the power spectral density distribution follows the distribution of the square value of σ.
[0052]
Weighted noise signal n at each rate₁', N₂', N₃', ..., n_{P + 1}'Is input to the sub-band combiners 46 (1) to 46 (P) of the combining circuit 45, respectively.
[0053]
Each of the subband synthesizers 46 (1) to 46 (P) includes an LPF (low-pass filter) and an HPF (high-pass filter) having the same cut-off frequency as the FIR type described above, Interpolation processing is performed on the digital signal, and the low frequency is cut off by HPF for one (higher frequency) input, and the high frequency by LPF for the other (low frequency) input. And the outputs of both filters are combined and output.
[0054]
The cutoff frequencies of the filters in the subband synthesizers 46 (1) to 46 (P) are 2fa, 4fa, 8fa, ..., where fa is the cutoff frequency of the subband synthesizer 46 (1) having the lowest frequency. 2^P-1In order of fa, it is set so as to be increased by a factor of 2 corresponding to the rate of the input noise signal, and is connected so as to synthesize in order from the low-rate noise signal.
[0055]
That is, as shown in FIG. 8, the two lowest-rate noise signals n₁', N₂'Is synthesized at the cut-off frequency fa in the subband synthesizer 46 (1), and its synthesized output and noise signal n₃'Is synthesized at the cut-off frequency 2fa in the sub-band synthesizer 46 (2), and the synthesized output and the noise signal n₄'Is synthesized at the cut-off frequency 4fa in the sub-band synthesizer 46 (3).
[0056]
Similarly, since the noise signals are synthesized in order from the lowest in the rate, the subband synthesizer 46 (P) changes the level of each band of the octave width according to the weighting coefficient as shown in FIG. A noise signal u (k) having a frequency characteristic is output.
[0057]
In the case of the filter unit 25 configured by the branching circuit 41, the weighting circuit 43, and the combining circuit 45 as described above, the cutoff frequency of the filter of each subband combiner 46 of the combining circuit 45 is fixed, so that the filter coefficient is variably controlled. The weighting factor σ that determines the characteristics of the filter₁, Σ₂, Σ₃, ..., σ_{P + 1}Is set from the characteristic coefficient setting means 30.
[0058]
The initial setting means 31 outputs a noise signal having a frequency characteristic corresponding to the characteristic coefficient (weighting coefficient in this case) from the filter unit 25 to the storage element in the filter (digital filter) of the synthesis circuit 46. A noise signal sequence having the same characteristics as the stored contents of each storage element in the state is initialized at the initial operation of the apparatus and when the weighting coefficient is changed.
[0059]
However, in this case, since the signal sequence output from the white noise generating means 21 cannot be simply substituted as described above, each signal is determined based on the white noise signal and information such as the weighting coefficient from the characteristic coefficient setting means 30. An initial value to be set in the storage element of the filter is calculated and set.
[0060]
That is, as described above, assuming that the noise signal n (1) generated when the white noise generating means 21 is in the initial stage of operation is known, the white noise generating means 21 generates the noise signal n (1) in a steady state. Each noise signal n output from the demultiplexing circuit 41₁~ N_{P + 1}In addition, the filter characteristics (transfer functions) of the subband synthesizers 46 of the synthesis circuit 45 are also known.
[0061]
Further, if the LPF and HPF storage elements in each of the sub-band synthesizers 46 (1) to 46 (P) of the synthesizer circuit 45 are both M-stages as described above, the final-stage sub-band synthesizer 46 (P). The normal M noise signals are input to each storage element of the filter of 2 in the first stage sub-band synthesizer 46 (1).^PWhen M noise signals are input, the mth stage (m is 1 to M) of the LPF of the i-th (i is any one of 1 to P) subband synthesizer 46 (i) at this time. Any one) storage value L of the storage element_i(M) and the storage value H of the mth storage element of HPF_i(M)
L_i(M) =_{j = 1}Σ^{i + 1}σ_j・ X_j(M)
H_i(M) =_{j = 1}Σ^{i + 1}σ_j・ Y_j(M)
It is expressed.
[0062]
Where x_j(M), y_j(M) is a constant string (a constant string when the weighting coefficient is 1) obtained from the transfer function of the LPF and HPF and the noise signal output from the white noise generating means 21, and as described above, the LPF and HPF. And the noise signal output from the white noise generating means 21 are known.
[0063]
Therefore, the constant sequence x_j(M), y_j(M) is obtained in advance and stored in the memory 31a, and at the initial stage of operation or when the weighting coefficient is changed, the initial value of the filter is obtained by the above calculation, and each subband synthesizer 46 (1) to 46 of the synthesizer circuit 45 is obtained. If set to (P), a noise signal u (k) having desired characteristics can be output immediately.
[0064]
The total number of times of the product-sum operation is M [(P + 1)²+ (P + 1) −2]. When M = 24 and P + 1 = 20, the number of times is 10032, and this product-sum operation can be completed in a short time.
[0065]
The initial setting means 31 uses the initial value L obtained by this calculation.₁(1) to L₁(M), L₂(1) to L₂(M), ..., L_P(1) to L_P(M), H₁(1) to H₁(M), H₂(1) to H₂(M) ... H_P(1) to H_P(M) is set in the LPF and HPF storage elements in each of the subband synthesizers 46 (1) to 46 (P) of the synthesis circuit 45, and then the white noise generation means 21 is instructed to output a noise signal. .
[0066]
If this initial setting is actually performed by inputting a noise signal from the white noise generating means 21, 2 as described above.^P-It is necessary to input M noise signals. If the input rate is 50 Hz, it takes about 70 hours. Even if the input rate is increased only during the initial setting, the combining circuit 45 is 2^P・ The total number of product-sum operations required to calculate M noise signals is 2M²(2^PTherefore, if M = 24 and P + 1 = 20 as described above, 60205 times product-sum operation is required, which takes a long time.
[0067]
As described above, by initializing each storage element of the digital filter of the filter unit 25 at the initial operation time or when changing the characteristic coefficient, the internal state of the filter unit 25 is immediately set to the same state as the steady state. The filter unit 25 can promptly output a noise signal having a frequency characteristic corresponding to the characteristic coefficient (weighting coefficient in this case) set by the characteristic coefficient setting unit 30.
[0068]
The noise generator 21 can be used alone or as a modulation signal generator of a signal generator that generates a clock signal with phase fluctuation.
[0069]
FIG. 9 shows a configuration of a jitter / wander generator 50 that generates a clock signal having phase fluctuations (jitter or wander) using almost the same configuration as that of the noise generator.
[0070]
In this figure, the white noise generating means 21, the filter unit 25, the characteristic coefficient setting means 30, the initial setting means 31, the multiplier 32, and the amplitude setting means 33 have the same configuration as that of the noise generating device 20, and therefore have the same reference numerals. It is attached.
[0071]
The jitter wander generator 50 inputs the output y (k) of the multiplier 32 to the frequency synthesizer 51.
[0072]
The frequency synthesizer 51 is composed of, for example, a DDS (direct digital synthesizer) or a PLL oscillator, and has a predetermined center frequency and a clock signal CK whose phase is modulated in accordance with the output y (k) of the multiplier 32. Output.
[0073]
On the other hand, the characteristic calculating unit 34 'is configured to generate the noise signal y (k) or the clock based on the characteristic coefficient from the characteristic coefficient setting unit 30, the amplitude coefficient A of the amplitude setting unit 33, and parameters set from an operation unit (not shown). The characteristics of the signal CK are obtained.
[0074]
For example, as an evaluation amount of a wander having a phase fluctuation of 10 Hz or less, TIErms (τ) (Root Mean Square Time Error), ADEV (τ) (Allan Deviation), MADEV (nτ₀) (Modified Allan Deviation), TDEV (nτ₀) (Time Deviation) and the like, but if these are actually obtained by measuring the clock signal CK, it takes a very long time (several hours or more) as described above.
[0075]
Therefore, in the jitter / wander generating apparatus 50, the characteristic calculation means 34 'selectively obtains the characteristic by performing the following calculation.
[0076]
TIErms (τ)
= [8∫S_x(F) sin²(Πfτ) df]^1/2
[0077]
ADEV (τ)
= [((16 / τ²) S_x(F) sin⁴(Πfτ) df]^1/2
[0078]
MADEV (nτ₀)
= {[16 / (n²τ₀)²] ∫ [sin⁶(Πfτ₀) / Sin²(Πfτ₀)] ・ S_x(F) df}^1/2          (N = 0, 1, 2, ..., N)
[0079]
TDEV (nτ₀)
= {(16 / 3n²) [Sin⁶(Πfτ₀) / Sin²(Πfτ₀)] S_x(F) df}^1/2                  (N = 0, 1, 2, ..., N)
[0080]
here,
S_x(F)
= Fc [(σ_aU · A) sin (πf / fs) / 2πfsin (πf / fc)]²・ | H (e^{jπf / fs}) ｜²
[0081]
The symbol ∫ is an integral from f = 0 to f = fh, the parameter fh is the maximum noise frequency, τ is the measurement time, τ₀Is the measurement sampling time, σ_aIs the standard deviation of white noise, fs is the sampling frequency of the white noise generating means 21, u is the DDS quantization step when the frequency synthesizer 51 is configured with DDS, and fc is the clock frequency of the D / A converter.
[0082]
A is an amplitude coefficient from the amplitude setting means 33, and | H (e^{jπf / fs}) | Is a frequency characteristic calculated based on the characteristic coefficient set by the characteristic coefficient setting means 31, and S_x(F) is a power spectrum of time error calculated based on the characteristic coefficient set by the characteristic coefficient setting means 31.
[0083]
The characteristic obtained by such an operation is displayed as a numerical value or a graph on the display unit 36 by the characteristic display means 35. However, the above operation does not measure the actual clock signal, but the characteristic coefficient, the amplitude coefficient, and the above-mentioned characteristic. Since it is calculated based on the parameters, it can be obtained in a short time, and the noise characteristics and the phase fluctuation characteristics thereof can be confirmed in advance when outputting the signal.
[0084]
In the above-described embodiment, the case where the digital filter included in the filter unit 25 is the FIR type has been described. However, this does not limit the present invention, and input data is stored while being shifted to a plurality of internal storage elements. Any digital filter having a structure for performing an operation can be used. For example, an IIR type filter can be applied in the same manner.
[0085]
【The invention's effect】
As described above, the noise generating apparatus according to claim 1 of the present invention stores the white noise generating means for generating a digital white noise signal and the digital signal while sequentially shifting it to a plurality of internal storage elements. A digital filter that performs a product-sum operation on the storage contents of the plurality of storage elements, and converts the noise signal output from the white noise generating means into a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient. Output filter unit, characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit, and each storage of the digital filter in a state where a noise signal having a frequency characteristic corresponding to the characteristic coefficient is output from the filter unit Initial setting means for initially setting a noise signal string equivalent to the stored contents of the element in each storage element of the digital filter at least at the initial operation of the device It is equipped with a.
[0086]
For this reason, since the internal state of the filter unit is immediately set to the same state as the steady state at the initial stage of operation, etc., a noise signal having a frequency characteristic corresponding to the characteristic coefficient set by the characteristic coefficient setting means is quickly output. Can be made.
[0087]
According to a second aspect of the present invention, there is provided a noise generating device comprising: white noise generating means for generating a digital white noise signal; and storing the digital signal while sequentially shifting the digital signal to a plurality of internal storage elements. A filter having a digital filter that performs a product-sum operation on the storage contents of the storage element, and converting the noise signal output from the white noise generating means into a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient and outputting the converted noise signal Unit, characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit, a multiplier for multiplying a noise signal output from the filter unit by a preset amplitude coefficient, and an arbitrary amplitude coefficient for the multiplier Noise output from the multiplier based on the amplitude setting means for setting the characteristic coefficient, the characteristic coefficient set in the filter unit from the characteristic coefficient setting means and the amplitude coefficient of the amplitude setting means It includes a characteristic calculating means for obtaining a degree in characteristics, and a characteristic display means for displaying the characteristics of the noise signal obtained by the characteristic calculating means.
[0088]
Therefore, it is convenient to know the noise characteristics in advance without measuring the output noise.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a noise generator according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a main part of the embodiment.
FIG. 3 is a block diagram showing a configuration of a main part of the embodiment.
FIG. 4 is a block diagram for explaining the operation of the embodiment;
FIG. 5 is a block diagram showing a modification of the main part of the embodiment.
6 is a timing chart for explaining the operation of the modified example of FIG.
7 is a diagram for explaining the operation of the modified example of FIG. 5;
8 is a diagram for explaining the operation of the modification of FIG. 5;
FIG. 9 is a block diagram showing a configuration of a jitter wander generator including a noise generator according to an embodiment of the present invention.
FIG. 10 is a block diagram showing a schematic configuration of a digital noise generator.
[Explanation of symbols]
20 Noise generator
21 White noise generation means
22 (1) to 21 (N) pseudo-random signal generator
23 Control circuit
25 Filter section
26 Digital filter
27 (1) to 27 (M) Memory element
28 (1) to 28 (M + 1) multiplier
29 Adder
30 characteristic coefficient setting means
31 Initial setting means
32 multiplier
33 Amplitude setting means
34, 34 'characteristic calculation means
35 Characteristic display means
36 Display
41 Demultiplexer circuit
42 (1) to 42 (P) 1/2 decimating circuit
43 Weighting circuit
44 (1) to 44 (P + 1) multiplier
45 Synthesis circuit
46 (1) to 46 (P) subband synthesizer
50 Jitter / Wander Generator
51 frequency synthesizer

Claims (2)

White noise generating means for generating a digital white noise signal;
The digital signal is stored in a plurality of internal storage elements while being sequentially shifted, and has a digital filter that performs a product-sum operation on the storage contents of the plurality of storage elements, and the noise signal output from the white noise generating means is A filter unit that converts a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient and outputs the noise signal;
Characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit;
A noise signal sequence equivalent to the storage content of each storage element of the digital filter in a state where a noise signal having a frequency characteristic corresponding to the characteristic coefficient is output from the filter unit, at least at the initial operation of the apparatus, A noise generating device comprising initial setting means for initial setting in each storage element. White noise generating means for generating a digital white noise signal;
The digital signal is stored in a plurality of internal storage elements while being sequentially shifted, and has a digital filter that performs a product-sum operation on the storage contents of the plurality of storage elements, and the noise signal output from the white noise generating means is A filter unit that converts a noise signal having a frequency characteristic corresponding to a preset characteristic coefficient and outputs the noise signal;
Characteristic coefficient setting means for setting an arbitrary characteristic coefficient for the filter unit;
A multiplier for multiplying a noise signal output from the filter unit by a preset amplitude coefficient;
Amplitude setting means for setting an arbitrary amplitude coefficient in the multiplier;
Based on the characteristic coefficient set in the filter unit from the characteristic coefficient setting means and the amplitude coefficient of the amplitude setting means, characteristic calculation means for obtaining the characteristic of the noise signal output from the multiplier,
A noise generating device comprising: characteristic display means for displaying the characteristic of the noise signal obtained by the characteristic calculation means.

Images