JP2005341212A - Modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulator capable of performing modulation precisely. <P>SOLUTION: The modulator provided with a variable vibrator for varying and outputting the amplitude of a modulation signal and a modulation part for modulating a clock signal with the modulation signal outputted from the variable modulator divides the frequency of a modulated signal outputted from the modulation part and adjusts the output level of the variable modulator based on the level of the carrier component of the modulated signal and the level ratio of a side band component. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a modulation apparatus that is used in, for example, a jitter generation apparatus and can perform modulation with high accuracy.

  Various circuits and devices that handle digital signals may not operate normally if there is jitter in the input signal. For this reason, it is necessary to measure in advance the maximum amount of jitter (jitter tolerance) that allows the circuit or device to operate normally.

  Therefore, a jitter generator measures the amount of jitter by outputting a phase-modulated clock signal. In order to calibrate the jitter generator, the modulation index (modulation degree) is calibrated using an external spectrum analyzer. There is also a jitter generator as in Patent Document 1 that automatically corrects the modulation index.

JP-A-10-132904

  Of these prior arts, a conventional jitter generator using an external spectrum analyzer will be described first with reference to FIG.

  In FIG. 4, the jitter generation device 10 includes a modulation signal generator 11, a variable amplitude device 12, and a modulation unit 13, and phase-modulates a clock signal 100 output from a signal generation device (not shown).

  The modulation signal generator 11 outputs a modulation signal 101. The variable amplitude unit 12 receives the modulation signal 101 of the modulation signal generator 11. The modulation unit 13 receives the clock signal 100 and modulates the clock signal 100 with the modulation signal 101. The external spectrum analyzer 20 observes the waveform of the modulated signal 102 from the jitter generator 10.

  Next, the operation of such a jitter generator 10 will be described. The modulation signal generator 11 generates a modulation signal 101 and outputs it to the variable amplitude unit 12. The amplitude of the modulation signal 101 is changed when the variable amplitude unit 12 is changed by a modulation index setting unit (not shown), and is input to the modulation unit 13. The modulation unit 13 modulates the clock signal 100 with the modulation signal 101 input via the variable amplitude unit 12 and outputs a modulated signal 102.

  The modulated signal 102 is input to a circuit to be measured (not shown). At this time, if no error occurs in the circuit under test, it is determined that it is within the jitter tolerance range. The user then adjusts the modulation index setter to change to the next modulation index to be tested. In this way, when the modulation index is gradually increased by the modulation index setting unit and an error occurs in the circuit under measurement, the jitter tolerance is measured by obtaining the modulation index at that time.

Next, a conventional jitter generator having an automatic calibration function will be described with reference to FIG.
In FIG. 5, a jitter generator 30 includes a modulation signal generator 31, a variable amplitude unit 32, a modulation unit 33, a band pass filter 34, a level detector 35, an A / D converter 36, a minimum detection unit 37, and a modulation index setting. And a phase modulation of the clock signal 103.

  The modulation signal generator 31 outputs a modulation signal 104. The variable amplitude unit 32 receives the modulation signal 104 of the modulation signal generator 31 and varies the amplitude of this signal. The modulation unit 33 modulates the clock signal 103 by the output of the variable amplitude unit 32 and outputs a modulated signal 105.

  The band pass filter 34 extracts only the carrier component (frequency of the clock signal 103 before modulation) from the modulated signal 105. The level detector 35 detects the signal level of the carrier component extracted by the band pass filter 34. The A / D converter 36 converts the analog signal output from the level detector 35 into a digital signal.

  Based on the digital signal output from the A / D converter 37, the minimum detection unit 37 detects that the carrier component has become minimum, that is, a carrier null point. The modulation index setting unit 38 sets the modulation index by adjusting the variable amplitude device 32. The memory 38a sequentially stores the current level of the modulated signal 105.

  Next, the calibration operation of such a jitter generator 30 will be described. First, the attenuation variable K of the variable amplitude device 32 is maximized to be in an unmodulated state. Here, the attenuation variable K is determined according to the accuracy required for calibration.

  The amplitude of the modulation signal 104 output from the modulation signal generator 31 is adjusted by the variable amplitude unit 32 so that the modulation index increases, and is input to the modulation unit 33. The modulator 33 modulates the clock signal 103 with the modulated signal 104 and outputs the modulated signal to the bandpass filter 34 and the circuit under measurement.

  In the band pass filter 34, only the carrier component is extracted from the modulated signal 105. The level detector 35 detects the level of the carrier component, and the A / D converter 36 converts it to a digital signal. The digital signal is input to the modulation index setting unit 38 via the minimum detection unit 37.

  The modulation index setting unit 38 takes in the signal output from the minimum detection unit 37 and increments the attenuation variable K of the variable amplitude device 32 until the minimum detection unit 37 detects the 20th carrier null point. Further, the modulation index setting unit 38 stores the modulation indices Z1 and Z2 of the first carrier null point and the 20th obtained carrier null point in the memory 38a.

  The modulation index setting unit 38 obtains correction data based on the values of the modulation indices Z1 and Z2 and the theoretical value of the modulation index at the carrier null point stored in advance in the memory 38a. Since the procedure for obtaining specific correction data is the same as that of the invention described in Patent Document 1, description thereof will be omitted.

  On the other hand, in the normal operation of the jitter generator 30, the modulation index setting unit 38 sets the modulation index using the calibration data obtained in this way. At this time, if an error does not occur in the circuit under test, it is determined that the jitter is within the physical strength range. The user then adjusts the modulation index setter to change to the next modulation index to be tested. As described above, when the modulation index is gradually increased by the modulation index setting unit and an error occurs in the circuit under measurement, the jitter tolerance is measured by obtaining the modulation index at that time.

  By the way, in order to perform such measurement with high accuracy, the modulation index of the modulated signals 102 and 105 actually output from the jitter generators 10 and 30 and the theoretical modulation index coincide with each other with high accuracy. There is a need.

  However, the modulated signals 102 and 105 are susceptible to fluctuations due to environmental changes such as temperature and changes with time, and a difference occurs in the modulation index between them. For this reason, in the conventional jitter generator 10 having no automatic calibration function, as shown in FIG. 4, the output of the jitter generator 10 is connected to the external spectrum analyzer 21 and the Bessel function curve shown in FIG. 6 is used. The jitter generator 10 has been calibrated.

  That is, the modulation index of the jitter generating apparatus 10 is gradually increased manually from zero to become a carrier null point (a value at which the level of the carrier component is minimized) in the spectrum displayed on the screen of the spectrum analyzer 20. At this time, the value of the modulation index setting unit of the jitter generator 10 is calibrated so as to coincide with the modulation index at which the Bessel function curve in FIG. 6 becomes zero (M1 to M6).

  However, the calibration method as described above requires a spectrum analyzer, and there is a problem that the connection work and operation become complicated.

  On the other hand, the modulation device shown in the jitter generation device 30 shown in FIG. 5 automatically corrects the modulation index display, so that connection work and operation of the spectrum analyzer are not required, but it can be calibrated only at the carrier null point. Since there is no difference from the method of using a spectrum analyzer, there is a problem that it cannot be modulated with high accuracy.

  The present invention focuses on this problem, and an object of the present invention is to provide a modulation device that can perform modulation with high accuracy.

In order to achieve such a problem, the invention according to claim 1 of the present invention is characterized in that a variable amplitude device for varying the amplitude of a modulation signal and outputting a clock signal by the modulation signal outputted from the variable amplitude device. In a modulation device comprising a modulation unit that modulates
The modulated signal output from the modulating section is divided, and the output level of the variable amplitude device is adjusted based on the ratio of the carrier component level and the sideband component of the modulated signal.

The invention according to claim 2
In a modulation apparatus comprising: a variable amplitude device that varies and outputs an amplitude of a modulation signal; and a modulation unit that modulates a clock signal with the modulation signal output from the variable amplitude device.
An A / D converter that converts the modulated signal output from the modulation unit into a digital signal;
An arithmetic unit for obtaining a level ratio between the carrier component of the modulated signal output from the A / D converter and the first sideband component;
A memory for storing a theoretical value in a Bessel function of a level ratio of a carrier component of the modulated signal, a level ratio of a first sideband component, and a modulation index;
A control unit that compares a level ratio of the arithmetic unit with a theoretical value of the memory and adjusts an output level of the variable amplitude device so as to coincide with the theoretical value.

The invention according to claim 3 is the invention according to claim 2,
The control unit includes a first step of reading the theoretical value of the memory, and a second step of comparing the level ratio of the computing unit with the theoretical value of the memory,
When the level ratio of the arithmetic unit is larger than the theoretical value of the memory in the second step, the output level of the variable amplitude device is adjusted little by little until the arithmetic unit level ratio matches the theoretical value of the memory,
When the level ratio of the arithmetic unit is smaller than the theoretical value of the memory, the output level of the variable amplitude unit is adjusted little by little until the arithmetic unit level ratio matches the theoretical value of the memory.

The invention according to claim 4 is the invention according to claim 2 or 3,
By providing a frequency divider that divides the modulated signal and outputs it to the A / D converter, the modulation index of the Bessel function is lowered.

The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The present invention is characterized in that it is used as a modulation means of a jitter generator.

The present invention has the following effects.
In the first to fourth aspects of the invention, since the Bessel function can be calibrated at any value, the modulation can be performed with high accuracy. Furthermore, since the number of parts can be reduced, the cost of the entire apparatus is reduced.

  In the invention according to claim 4, by dividing the frequency of the modulated signal, the modulation index in the Bessel function is lowered, so that the level ratio becomes high and the modulation can be performed with high accuracy.

  According to the fifth aspect of the present invention, since it is used in the jitter generator, the jitter tolerance measurement can be performed with high accuracy.

  This will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The jitter generator 40 includes a modulation signal generator 41, a variable amplitude unit 42, a modulation unit 43, a frequency divider 44, an A / D converter 45, a calculation unit 46, a memory 47, and a control unit 48. Is to modulate.

  The modulation signal generator 41 outputs a modulation signal 107, for example, a sine wave. The variable attenuator 42 receives the modulation signal 107 from the modulation signal generator 41. The modulation unit 43 phase-modulates the clock signal 108 by the output of the variable attenuator 42 and outputs the modulated signal 108 to a circuit to be measured (not shown). The frequency divider 44 divides the modulated signal 108 of the modulation unit 43.

  The A / D converter 45 converts the signal output from the frequency divider into a digital signal. The computing unit 46 obtains the level ratio between the carrier component and the first sideband component in the modulated signal 108 based on the digital signal output from the A / D converter 45. Here, the computing unit 46 is an FFT (Fast Fourier Transform) computing unit, and extracts which frequency component is contained in the modulated signal 108 by using Fourier transform.

  The memory 47 stores the theoretical value of the level ratio of the carrier component level of the modulated signal 108 and the first sideband component for each modulation index of the Bessel function in the storage unit. The control unit 48 is a CPU, compares the level ratio of the calculation unit 46 with the theoretical value of the memory 47, and adjusts the output level of the variable amplitude device 42 so as to match the theoretical value.

Next, the operation of such a jitter generator 40 will be described.
The modulation signal 107 generated by the modulation signal generator 41 is input to the modulation unit 43 via the variable amplitude device 42. The modulation unit 43 modulates the clock signal 106 with the modulation signal 107 input via the variable amplitude unit 42 and outputs the modulated signal 108.

  The operation of the modulation unit 43 will be described in more detail. As the clock signal 106 input to the modulation unit, for example,

The signal which consists of is input. Here, fc is the frequency of the carrier signal, and A is the amplitude of the carrier signal. The modulation signal 107 input via the variable amplitude device 42 is

Can be expressed as Here, fs is the frequency of the modulation signal, and B is the amplitude of the modulation signal. From the modulation unit 42,

A signal consisting of Here, β is a modulation index. In the case of frequency modulation, the modulated signal 108 output from the modulation unit 42 is

It is expressed. Here, Δf is the maximum frequency shift. Therefore, if Δf / fs = β, frequency modulation can be handled in the same manner.

  The modulated signal 108 is input to a circuit to be measured (not shown) and also input to the frequency divider 44.

  The frequency divider 44 divides the frequency of the modulated signal 108 to reduce the modulation index of the Bessel function and outputs it to the A / D converter 45. For example,

からなる信号を分周器４４に入力すると、分周されて

When a signal consisting of

Is output to the A / D converter 45. Here, N is a frequency division value. That is, by setting the frequency to 1 / N, the modulation index of the modulated signal 108 also becomes 1 / N.

Conditions and methods for frequency division by such a frequency divider 44 are as follows.
First, the modulation index is 2.405 or higher. The modulation index 2.405 is one of the carrier null points. Below this value, the level ratio between the clock signal and the first sideband can be clearly identified.

  For example, when N = 10 and modulation index = 20, the modulation index of the carrier component is converted to 2.0. In this manner, the modulation index is lowered to 2.405 or less by the frequency divider 44.

  Second, the frequency of the modulated signal 108 is outside the rated range of the A / D converter 45. This is because the frequency of the clock signal 106 needs to be ½ or less of the sampling frequency of the A / D converter 45 in order for the A / D converter 45 to perform sampling accurately. In this case, the frequency divider 44 changes the frequency division value so that the modulation index is 2.405 or less and becomes half the sampling frequency of the A / D converter 45 according to an instruction from the control unit 48. .

  The A / D converter 45 converts the analog signal output from the frequency divider 44 into a digital signal and outputs the digital signal to the arithmetic unit 46.

  Based on the digital signal input from the A / D converter 45, the calculation unit 46 obtains the level ratio between the carrier component and the first sideband component of the modulated signal 108 and outputs it to the control unit 48. The control unit 48 compares the level ratio between the carrier component and the first sideband component obtained from the calculation unit 46 with the theoretical value stored in the memory 47, and outputs the output from the variable amplitude device 42 so as to match the theoretical value. Adjust the level. Hereinafter, a processing procedure for matching with the theoretical value will be specifically described.

  FIG. 2 is a flowchart showing an embodiment of the present invention. In the following description, a case where the level ratio X between the carrier component and the first sideband component obtained from the calculation unit 46 is higher than the theoretical value Y of the memory will be described.

  First, the control unit 48 reads the theoretical value Y stored in the memory 48 (step A1). The calculator 46 obtains the level ratio X between the carrier component and the first sideband component (step A2). And the control part 48 judges whether X is in agreement with Y by comparing this level ratio X with the theoretical value Y (step A3).

  Here, if X coincides with the theoretical value Y, the calibration is terminated. However, since the level ratio X is larger than the theoretical value Y, the magnitude relationship between X and Y is judged (step A4), and the variable amplitude device The attenuation variable K of 42 is incremented (step A5). As a result, the amplitude of the modulation signal 107 output from the variable amplitude device 42 is reduced. When these series of processes are completed, the process returns to step A2, and the same process is repeated until the level ratio X matches the theoretical value Y and the calibration is completed. The attenuation variable K is determined according to the accuracy required for calibration.

  Since the memory 47 stores the theoretical value of the level ratio of the carrier component level of the modulated signal 43a and the first sideband component for each modulation index of the Bessel function, the comparison with the theoretical value is performed by carrier null. It is also performed outside of points.

  In this way, not only the carrier null point but also the modulation index of the Bessel function can be calibrated at any value, so that the modulation index of the jitter generator 40 can be calibrated with high accuracy. Therefore, jitter tolerance measurement and the like can be performed with high accuracy.

  Further, since the modulation index of the clock signal of the modulated signal 43a is obtained by setting the frequency of the modulated signal to 1 / N, the modulation index of the modulated signal 43a can be converted to 2.405 or less. The reason why calibration is performed in the region where the modulation index is 2.405 or less will be described in detail with reference to FIG.

  FIG. 3 is a Bessel function curve, where the vertical axis indicates the signal level, the horizontal axis indicates the modulation degree, a indicates the clock signal clock signal, and b indicates the first sideband. In FIG. 3, it can be seen that the ratio of the level of the clock signal a and the level of the first sideband b is greatly different before and after the modulation index of 2.405.

  That is, when the modulation index is 2.405 or more, even if the modulation index increases or decreases, the level ratio of the clock signal and the first sideband is almost the same even if the modulation index increases or decreases. By setting it to 405 or less, it becomes possible to compare with the theoretical value in a region where the level ratio between the clock signal and the first sideband is clearly understood, and the modulation index of the jitter generator 40 can be calibrated with high accuracy.

  In the embodiment of FIG. 1, an example in which the calculation unit 46 is an FFT calculator is shown, but a DSP (Digital Signal Processor) may be used.

  Further, the CPU 46 may be configured without the calculation unit 46 and the control unit 48, and the CPU may have a theoretical value table stored in the memory 47.

  The timing for calibrating the modulation device 40 may be arbitrarily set by the user or whenever the modulation index setting is changed.

  Furthermore, although the jitter generator has been described as an application of the phase modulator, the present invention is not limited to this.

It is the block diagram which showed one Example of this invention. It is the flowchart which showed one Example of this invention. It is a wave form diagram showing the Bessel function curve of the present invention. It is a prior art jitter generator. This is another conventional jitter generator. It is the figure which showed the Bessel function curve.

Explanation of symbols

41 Modulation signal generator 42 Variable amplitude unit 43 Modulation unit 44 Frequency divider 45 A / D converter 46 Operation unit 47 Memory 48 Control unit 107 Modulation signal 108 Modulated signal

Claims (5)

In a modulation apparatus comprising: a variable amplitude device that varies and outputs an amplitude of a modulation signal; and a modulation unit that modulates a clock signal with the modulation signal output from the variable amplitude device.
Modulation characterized by dividing the modulated signal output from the modulation section and adjusting the output level of the variable amplitude device based on the ratio of the carrier component level and the sideband component of the modulated signal apparatus. In a modulation apparatus comprising: a variable amplitude device that varies and outputs an amplitude of a modulation signal; and a modulation unit that modulates a clock signal with the modulation signal output from the variable amplitude device,
An A / D converter that converts the modulated signal output from the modulation unit into a digital signal;
An arithmetic unit for obtaining a level ratio between the carrier component of the modulated signal output from the A / D converter and the first sideband component;
A memory for storing a theoretical value in a Bessel function of a level ratio of a carrier component of the modulated signal, a level ratio of a first sideband component, and a modulation index;
A modulation device comprising: a control unit that compares a level ratio of the arithmetic unit with a theoretical value of the memory and adjusts an output level of the variable amplitude device so as to coincide with the theoretical value. The control unit includes a first step of reading the theoretical value of the memory, and a second step of comparing the level ratio of the computing unit with the theoretical value of the memory,
When the level ratio of the arithmetic unit is larger than the theoretical value of the memory in the second step, the output level of the variable amplitude device is adjusted little by little until the arithmetic unit level ratio matches the theoretical value of the memory,
3. The output level of the variable amplitude unit is gradually adjusted until the arithmetic unit level ratio and the theoretical value of the memory coincide with each other when the level ratio of the arithmetic unit is smaller than the theoretical value of the memory. Modulation device.   4. The modulation apparatus according to claim 2, wherein the modulation index of the Bessel function is lowered by providing a frequency divider that divides the modulated signal and outputs the frequency-divided signal to the A / D converter. 5. The modulation device according to claim 1, wherein the modulation device is used as a modulation means of a jitter generation device.

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