JP3277325B2 - Jitter transfer characteristic measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a jitter transfer characteristic measuring apparatus for measuring a jitter transfer characteristic of a transmission device for relaying a digital signal or the like, the jitter transmission of a transmission device having different input bit rates and output bit rates. The present invention relates to a technique for measuring characteristics with high accuracy.

[0002]

2. Description of the Related Art In a transmission device that reproduces and outputs an input digital signal, if the device itself imparts a phase fluctuation (jitter) to the signal, such transmission devices are connected in multiple stages to transmit a signal. If the path is extended, the amount of jitter of the signal increases, and the original data cannot be transmitted accurately.

[0003] Therefore, in such a transmission device, the jitter amount of the output signal is 0.1 dB smaller than the jitter amount of the input signal.
It is defined as follows. When evaluating the jitter of a device that transmits a digital signal, the data signal itself cannot be targeted, so the clock signal extracted from the input / output data signal is targeted. A signal input to the measurement circuit and a signal output from the circuit under test indicate this clock signal.

In order to measure the jitter transfer characteristic, a jitter transfer characteristic measuring device 10 shown in FIG. 10 has been conventionally used.

The jitter transfer characteristic measuring apparatus 10 includes a jitter generator 11 for generating a signal having jitter and outputting the signal from an output terminal 10a, and a jitter detector 12 for detecting a jitter amount of a signal input to an input terminal 10b. And

[0006] The jitter generator 11 includes a voltage-controlled oscillator 11
a and a reference signal having a frequency f1 output from the reference signal oscillator 11b are input to a phase comparator 11c, and the phase comparator 11c
An error signal corresponding to the phase difference between the output signal of the voltage controlled oscillator 11a and the reference signal is extracted from the output signal of c by the low-pass filter 11d, and the error signal and the modulation signal output from the modulation signal generator 11e are extracted. Is added by an adder 11f, and the addition result is used as a control signal as a voltage-controlled oscillator 11a.
To enter.

In the jitter generator 11 having the PLL configuration,
By the control of the loop, the signal output from the voltage controlled oscillator 11a is output from the output terminal 10a in a state where the frequency matches the frequency of the reference signal and the phase is modulated in proportion to the amplitude of the modulation signal, and Input to the circuit 1. Here, the amplitude of the modulation signal is proportional to the jitter amount Jt set in the modulation signal generator 11e.

On the other hand, the jitter detecting section 12 includes a signal output from the crystal oscillation type voltage controlled oscillator 12a at a frequency corresponding to the voltage of the control signal and an input signal input to the input terminal 10b (output of the circuit under test 1). Signal) and the phase comparator 12b
To remove the frequency components of the output signal of the voltage controlled oscillator 12a and the input signal from the output signal of the phase comparator 12b by a low-pass filter 12c, and output an error signal (a signal of the jitter generator 11) corresponding to the phase difference between the two. A signal below the frequency of the modulated signal) is extracted and input to the jitter amount detection circuit 12d. The error signal is passed through an active filter 12e to increase the low-frequency gain and input the control signal to the voltage-controlled oscillator 12a.

In the jitter detecting section 12 having the PLL circuit configuration, the voltage of the control signal is changed by controlling the loop so that the phase of the signal output from the voltage controlled oscillator 12a is always locked at the center phase of the input signal. The jitter amount detection circuit 12d detects the amplitude of the error signal, and detects the jitter amount Jr from the amplitude.

The control section 13 designates a predetermined amount of jitter Jt to the modulation signal generator 11e of the jitter generation section 11 and varies the frequency (jitter frequency) of the modulation signal while controlling the jitter detection section 12 for the amount of jitter Jt. Detected jitter amount Jr
Is calculated as the amount of jitter transmission.

In the jitter transfer characteristic measuring apparatus 10 configured to apply the phase-modulated signal to the circuit under test 1 and perform phase detection on the output of the circuit under test 1, If the relationship with the amount of jitter detected by the jitter detector 12 is not correctly calibrated, the jitter transfer characteristic of the circuit under test 1 cannot be accurately measured.

For this reason, conventionally, an input terminal 10a and an output terminal 10b are directly connected by a cable, and an error of a detected jitter amount Jr with respect to a specified jitter amount Jt is obtained for each frequency of the jitter. The jitter transfer amount when the circuit under test 1 is connected between the input terminal 10a and the output terminal 10b is corrected by the error data to determine the jitter transfer characteristic of the circuit under test 1.

[0013]

In conventional digital signal transmission equipment, since the input bit rate and the output bit rate are equal, the frequency of the output signal of the jitter generator 11 and the input signal frequency of the jitter detector 12 ( (Synchronizable frequency) is set to be the same, but recently, transmission equipment having different input and output bit rates may be used for the submarine transmission line.

However, it has been difficult to accurately measure the jitter transfer characteristics of transmission devices having different input / output bit rates by the above-described conventional jitter transfer characteristic measuring apparatus.

For example, a transmission device having an input frequency of 10 GHz and an output frequency of 11 GHz is used as the circuit under test 1, and the output frequency of the jitter generating section 11 is set to 10 GHz in order to measure the jitter transfer characteristic of the transmission device with the above-mentioned conventional measuring device. It is conceivable to set the input frequency of the jitter detector 12 to 11 GHz.

However, this does not allow for accurate calibration of the apparatus. That is, the output terminal 10a is used for calibration.
When a signal is directly connected between the input terminal 10b and the input terminal 10b, a signal of 10 GHz is input to the jitter detection unit 12, but the voltage controlled oscillator 12a of the jitter detection unit 12 is a crystal oscillation type corresponding to 11 GHz, It is usually not possible to vary up to 10 GHz.

Even if the jitter detecting section 12 can be synchronized in the range of 10 GHz to 11 GHz by using a voltage controlled oscillator 12a having a large frequency variable width, the response characteristic of the loop of the jitter detecting section 12 is 11 GHz.
There is a large difference between the state synchronized with z and the state synchronized with 10 GHz. Even if the jitter transmission amount detected from the signal of 11 GHz is corrected with the error data obtained in the state synchronized with 10 GHz, the accurate transmission amount can be obtained. You can't get it.

Conversely, the frequency range of the output signal of the jitter generator 11 is expanded to include 10 GHz and 11 GHz, and the signal of 11 GHz is input from the jitter generator 11 to the jitter detector 12 at the time of calibration, and at the time of measurement. It is conceivable that a 10 GHz signal is input to the circuit under test 1 from the jitter generator 11, but as described above, the frequency variable width of the voltage-controlled oscillator 11a of the jitter generator 11 and the frequency of the reference signal generator 11b are increased. Set the jitter generator 11 to 10 GH to 1
Even if the synchronization can be performed within the range of 1 GHz, the response characteristics of the loop of the jitter generator 11 are greatly different between the state synchronized with 10 GHz and the state synchronized with 11 GHz, and the amount of jitter with respect to the modulation signal is different.

It is an object of the present invention to solve this problem and to provide a jitter transfer characteristic measuring device capable of accurately measuring jitter transfer characteristics of a circuit under test having different input / output frequencies.

[0020]

In order to achieve the above object, a jitter transfer characteristic measuring apparatus according to a first aspect of the present invention measures a transfer characteristic with respect to a jitter of a circuit to be measured having a difference between input and output frequencies. Transfer characteristic measuring apparatus for outputting a signal having a frequency equal to the input frequency of the circuit under test and an output terminal (20a) and an input terminal (20b) for inputting and outputting a signal. A jitter generating section (21) that performs phase modulation by a modulation signal and outputs the output from the output terminal; and a frequency conversion section (30) that mixes a signal input to the input terminal with a local oscillation signal whose frequency can be switched and performs frequency conversion. ), A phase detection of a signal output from the frequency conversion unit, and a jitter detection unit (35) for detecting a jitter amount thereof; an operation unit (45); Mode designating means for designating either a calibration mode in which the output terminal and the input terminal are directly connected or a measurement mode in which the circuit to be measured is connected between the output terminal and the input terminal ( 51) and when the calibration mode is designated, the signal input from the jitter generator to the input terminal is converted to a predetermined frequency different from the input / output frequency of the circuit under test, and input to the jitter detector. When the measurement mode is designated, the frequency of the local oscillation signal of the frequency conversion unit is changed so that the signal input from the circuit under test to the input terminal is converted to the predetermined frequency and input to the jitter detection unit. Frequency switching means (54) for switching, a jitter frequency varying means (55) for varying the frequency of the modulated signal of the jitter generator within a predetermined range, and the predetermined jitter Transmission amount calculating means (56) for calculating, for each frequency of the modulated signal, the ratio of the jitter amount detected by the jitter detection section to the jitter amount, and the jitter transmission amount calculated by the jitter transmission amount calculating means in the measurement mode. Correcting means for correcting the jitter transfer amount of the circuit under test by correcting the jitter transfer amount calculated by the jitter transfer amount calculating means in the calibration mode (58).
And output means (59, 46) for outputting the jitter transfer characteristic of the circuit-under-test determined by the correction means.

According to a second aspect of the present invention, there is provided a jitter transfer characteristic measuring apparatus for measuring a transfer characteristic of a circuit under test having a difference between input and output frequencies with respect to jitter. An output terminal (20a) and an input terminal (20b) for inputting and outputting a signal, and a signal having a frequency different from the input / output frequency of the circuit under test is phase-modulated by a modulation signal having an amplitude corresponding to a predetermined amount of jitter and output. A jitter generator (21 '); a frequency converter (30') for mixing the output signal of the jitter generator with a local oscillation signal whose frequency can be switched to perform frequency conversion and outputting from the output terminal; A jitter detector (35 ') for phase-detecting a signal input to an input terminal and detecting a jitter amount thereof.
A calibration mode performed in a state where the output terminal and the input terminal are directly connected in accordance with an operation of the operation unit (45) and the operation unit, or a circuit to be measured between the output terminal and the input terminal. And a mode designating means (51) for designating any one of the measurement modes to be performed in a state where is connected, and when the calibration mode is designated, the output signal of the jitter generating section is set to a frequency equal to the output frequency of the circuit under test. Converted and output from the output terminal, when the measurement mode is designated, so that the output signal of the jitter generator is converted to a frequency equal to the input frequency of the circuit under test and output from the output terminal, Frequency switching means (54 ') for switching the frequency of the local oscillation signal of the frequency conversion section; and a jitter frequency variable means for varying the frequency of the modulation signal of the jitter generation section within a predetermined range. And (55), said predetermined amount of jitter and the jitter transfer amount calculating means the ratio of the amount of jitter detected by the jitter detection unit for calculating for each frequency of the modulation signal (5
6) correcting the jitter transfer amount calculated by the jitter transfer amount calculating means in the measurement mode with the jitter transfer amount calculated by the jitter transfer amount calculating means in the calibration mode, and And output means (59, 4) for outputting the jitter transfer characteristic of the circuit-under-test determined by the correction means.
6).

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of a jitter transfer characteristic measuring device 20 according to an embodiment of the present invention.

This jitter transfer characteristic measuring device 20 is for measuring a circuit under test (transmission equipment) having an input frequency F1 (for example, 10 GHz) and an output frequency F2 (for example, 11 GHz). Converter 3
0, a jitter detection unit 35, an operation unit 45, a display device 46, and a control unit 50.

The jitter generator 21 outputs a signal having jitter from the output terminal 20a, and outputs the signal from the voltage controlled oscillator 22 at a frequency corresponding to the voltage of the control signal, as shown in FIG. The signal is frequency-divided by a frequency divider 23, and this frequency-divided signal and a reference signal output from a reference signal generator 24 are input to a phase-frequency comparator 25, and a low-pass filter 26 controls the phase-frequency comparator 25. An error signal corresponding to the phase difference between the frequency-divided signal and the reference signal is extracted from the output signal, and the error signal and the modulation signal output from the modulation signal generator 27 are added by an adder 28 to the voltage-controlled oscillator 22. It has a PLL configuration that is input as a control signal.

Here, the center of the free-running oscillation frequency of the voltage controlled oscillator 22 is set to F1, and the frequency division ratio of the frequency divider 23 is set to N.
Assuming that the frequency is 1 (for example, 16), the frequency F3 (for example, 625 MHz) of the reference signal is set to F1 / N1, so that the voltage control oscillator 22
From the frequency F whose phase changes according to the amplitude of the modulation signal
1 is output.

The modulation signal generator 27 controls the control unit 5 at a frequency equal to the jitter frequency Fj designated by the control unit 50.
A modulation signal having an amplitude corresponding to the designated jitter amount Jt from 0 is output to the adder 28.

As shown in FIG. 1, the frequency converter 30 inputs the input signal input to the input terminal 20b and the local signal output from the local signal generator 31 to the mixer 32, and A signal component of a predetermined frequency F4 (for example, 2.5 GHz) is extracted by the filter 33 from the 32 mixed components. The filter 33 may be of a low-pass type or a band-pass type.

The local oscillator 31 is composed of a crystal oscillator capable of oscillating a signal having a very small phase fluctuation so as not to affect the jitter of the input signal, and converts the signal of the input frequency F1 and the output frequency F2 of the circuit under test. Two frequencies F5 (= F1−F4 or F1 + F4) and F6 (= F2) so that they can be converted to a frequency F4 different from those frequencies.
-F4 or F2 + F4) of the control unit 50
Is configured to be able to output the specified one.
Also, from the above frequency relationship, the input frequency F1 and the local oscillation signal
The frequency of the difference from the frequency F5 becomes F4, and the output frequency F
The frequency of the difference between 2 and the frequency F6 of the local oscillation signal is F4,
The filter 33 extracts the frequency components of these differences.
Will be.

As shown in FIG. 3, the jitter detector 35 divides the frequency F4 signal output from the frequency converter 30 by a frequency divider 36, and divides the frequency-divided signal by a crystal oscillation type voltage. The output signal of the control oscillator 37 is compared with the phase frequency
8 from the output signal of the phase frequency comparator 38 and the divided signal and the voltage controlled oscillator 3 by the low-pass filter 39.
7 removes the frequency component of the output signal of No. 7 and extracts an error signal corresponding to the phase difference between the two, further increases the low-frequency gain through the active filter 40 and inputs the error signal to the voltage-controlled oscillator 37 as a control signal. The jitter amount detection circuit 41 detects the amount of jitter of the input signal based on the amplitude of the error signal.

Here, for example, the center of the free-running oscillation frequency of the voltage controlled oscillator 37 is the frequency F7 (for example, 62) obtained by dividing the frequency F4 by the frequency dividing ratio N2 (for example, 4) of the frequency divider 36.
5 MHz), when a signal having a frequency F4 with jitter is input from the frequency conversion unit 30, the phase is locked to the center phase of the frequency-divided signal from the voltage controlled oscillator 37 by the loop pull-in control. The signal of the frequency F7 is output, and the voltage of the error signal output from the low-pass filter 39 changes according to the phase change of the frequency-divided signal.

The jitter amount detection circuit 41 obtains the amount of jitter of the frequency-divided signal from the amplitude of the error signal, multiplies the amount of jitter by the frequency division ratio (N2) of the frequency divider 36, and inputs the signal input to the input terminal 20b. Is detected.

The operation unit 45 is used to specify an operation mode, start measurement, set a jitter amount, and the like. Further, the display device 46 is configured by a CRT or a liquid crystal display capable of displaying a graph of the measurement result.

The control unit 50 is constituted by a microcomputer including a CPU, a ROM, a RAM, and the like. FIG. 1 shows the functions of the programs recorded in the ROM as blocks.

As shown in FIG. 1, the control unit 50 includes a mode designating unit 51, a measurement starting unit 52, a jitter amount setting unit 53, a frequency switching unit 54, a jitter frequency varying unit 55, a jitter transmission amount calculating unit. 56, a memory 57, a correction means 58, and a display control means 59.

The mode designating means 51 designates the operation mode inside the control unit 50 to be either the calibration mode or the measurement mode in accordance with the operation of the operation unit 45. Here, the calibration mode is a mode for obtaining error data by directly connecting the output terminal 20a and the input terminal 20b with a cable, and the measurement mode is for connecting a circuit to be measured between the output terminal 20a and the input terminal 20b. In this mode, the jitter transfer characteristic of the circuit under test is determined.

The measurement starting means 52 starts the operation in the calibration mode and the measurement mode in accordance with the operation of the operation unit 45.

The jitter amount setting means 53 sets a predetermined amount of jitter Jt for the modulation signal generator 27 of the jitter generation section 21 in accordance with the operation of the operation section 45.

When the calibration mode is designated, the frequency switching means 54 controls the local oscillator 3 of the frequency converter 30.
1 is set to the frequency F5, the signal input from the jitter generator 21 to the input terminal 20b is converted to a frequency F4 different from the input / output frequency of the circuit under test, and jitter is detected. When the measurement mode is designated, the frequency of the local oscillation signal is set to the frequency F6, and the signal input from the circuit under test to the input terminal 20b is converted to the frequency F4. The signal is input to the jitter detector 35.

The jitter frequency varying means 55 varies the frequency of the modulation signal output from the modulation signal generator 27 of the jitter generator 21 within a predetermined range when the measurement start means 52 instructs the start of measurement.

In the calibration mode, the jitter transmission amount calculation means 56 is provided by the jitter generation section 21 by the jitter amount setting means 53.
Is calculated for each frequency of the modulated signal as error data E and stored in the memory 57. In the measurement mode, the jitter amount setting means 53 is used. The jitter generator 21
Is calculated for each frequency of the modulated signal as jitter transmission amount data JT and stored in the memory 57 as jitter transmission amount data JT. Note that the calculated jitter transmission amount data JT may be directly output to the correction unit 58 without being stored in the memory 57.

The correction means 58 calculates the jitter transmission amount JT calculated by the jitter transmission amount calculation means 56 in the measurement mode.
Is corrected by the error data E stored in the memory 57, and the jitter transmission amount JT ′ for each frequency of the circuit under test is
That is, the jitter transfer characteristic is obtained.

The display control means 59 constitutes an output means of this embodiment together with the display device 46, and serves to display and output the jitter transfer characteristic of the circuit under test obtained by the correction means 58. The horizontal axis indicates the jitter frequency and the vertical axis indicates the amount of jitter transmission on the screen of the device 46, and the jitter transfer characteristic of the circuit under test obtained by the correction means 58 is displayed on these coordinates. It should be noted that print control means and a printer may be provided as output means to print out the jitter transfer characteristics of the circuit under test.

In the jitter transfer characteristic measuring apparatus 20 configured as described above, as shown in FIG.
When the calibration mode is designated by the operation unit 45 in a state where the signal is directly connected to the input terminal 20 b by the cable 2, the frequency switching unit 54 controls the frequency of the local oscillation signal of the local oscillation signal generator 31 of the frequency conversion unit 30. Is set to the frequency F5.

In this state, the signal of the frequency F1 output from the jitter generator 21 is output from the output terminal 20a and the input terminal 2
The signal is input to the frequency conversion unit 30 via Ob, is converted to a frequency F4 by the frequency conversion unit 30, and is input to the jitter detection unit 35.

Here, when the start of measurement is instructed by operating the operation unit 45, the frequency Fj of the modulation signal of the modulation signal generator 27 is changed by the jitter frequency varying means 55 within a predetermined frequency band to f1, f2,. , Fm and the jitter amount setting means 53, and the jitter generation amounts Jt (1), Jt (2),
.., When Jt (m) is set, the jitter detector 35
From the jitter amounts Jc (1), Jc (2),
.., Jc (m) are output.

Detected jitter amounts Jc (1) to Jc
(M) is input to the jitter transfer amount calculating means 56, and error data E1, E2,... For each frequency f1, f2,.
, Em is: E1 (dB) = 20 · log [Jc (1) / Jt (1)] E2 (dB) = 20 · log [Jc (2) / Jt (2)] …… Em (dB) = 20 · log [Jc (m) / Jt (m)] and is stored in a predetermined area of the memory 57.

Then, as shown in FIG.
When the circuit under test 1 is connected between the terminal a and the output terminal 20b, and the measurement mode is designated by the operation unit 45, the frequency switching unit 54 controls the frequency of the local oscillation signal of the local oscillation signal generator 31 of the frequency conversion unit 30. Is switched to the frequency F6.

In this state, the signal of the frequency F1 is input from the jitter generator 21 to the circuit under test 1 via the output terminal 20a, and the signal of the frequency F2 from the circuit under test 1 is frequency-converted via the input terminal 20b. This will be input to the unit 30.

At this time, since the frequency of the local oscillation signal of the frequency conversion unit 30 has been switched to the frequency F6, the signal of the frequency F2 input to the input terminal 20b is converted to the frequency F4 in the same manner as at the time of calibration. And input to the jitter detector 35.

Here, when the start of measurement is instructed by operating the operation unit 45, the frequency Fj of the modulation signal of the modulation signal generator 27 is changed to f1, f2,. fm, and the jitter generation amount Jt (1), Jt (2),
When Jt (m) is set, the jitter amount Jr (1), Jr (2),.
Jr (m) is detected.

The detected jitter amounts Jr (1), Jr
(2),..., Jr (m) are jitter transmission amount calculating means 56
, And JTm for each of the frequencies f1, f2,..., Fm, are JT1 (dB) = 20 · log [Jr (1) / Jt (1)] JT2 (dB) = 20 · log [Jr (2) / Jt (2)]... JTm (dB) = 20 · log [Jr (m) / Jt (m)] and stored in a predetermined area of the memory 57. Or output to the correction means 58.

Then, the following correction calculation is performed by the correction means 58: JT1 '= JT1-E1 JT2' = JT2-E2... JTm '= JTm-Em, and the amount of jitter transmission JT1 to JTm for each frequency. Are corrected by the error data E1 to Em, respectively, and the corrected jitter transmission amounts JT1 ′ to JTm ′ are displayed by the display control unit 5.
9 is output.

As shown in FIG. 6, for example, the display control means 59 displays the coordinates of the jitter frequency on the horizontal axis and the amount of jitter transmission on the vertical axis on the screen of the display device 46, and displays the corrected jitter transmission on these coordinates. The amounts JT1 'to JTm' are displayed so that the jitter transfer characteristics of the circuit under test 1 can be visually recognized on the screen.

As described above, the jitter characteristic measuring apparatus 20 according to the embodiment includes a signal of the frequency F1 input to the input terminal 20b for calibration and a signal of the frequency F2 input to the input terminal 20b for measurement. Is converted into the same frequency F4 by the frequency conversion unit 30 and input to the jitter detection unit 35. Therefore, it is necessary to completely change the operating conditions of the jitter generation unit 21 and the jitter detection unit 35 between the time of calibration and the time of measurement. In addition, since the frequency conversion unit 30 has little effect on the jitter transfer characteristics, the jitter transfer characteristics of the circuit under test having different input and output frequencies can be accurately measured.

In the above embodiment, the frequency converter 3
0 is provided between the input terminal 20b and the jitter detector 35. However, as in the jitter transfer characteristic measuring device 20 'shown in FIG. 7, the frequency converter 30' is provided between the jitter generator 21 'and the output terminal 20b. It is also possible to provide.

Here, the jitter generating section 21 'is the same as that shown in FIG.
The circuit under test 1 has the same configuration as the jitter generator 21 shown in FIG.
Input / output frequency F1 (10 GHz), F2 (11 GHz)
z), the center of the free-running oscillation frequency of the voltage-controlled oscillator 22 (for example, 2.5 GHz) and the frequency dividing ratio N1 of the frequency divider 23 (for example, 4 ) And the frequency of the reference signal of the reference signal generator 23 (for example, 625 MHz).

The jitter detector 35 'has the same configuration as the jitter detector 35 shown in FIG. 3, and the input frequency (synchronous frequency) of the output frequency F2 (11 GHz) of the circuit under test 1 is changed.
The division ratio N2 (for example, 16) of the frequency divider 36 and the center (for example, 687.5 MHz) of the free-running oscillation frequency of the voltage controlled oscillator 37 are set so as to be equal to z).

The local signal generator 31 of the frequency converter 30 'converts the two frequencies F12 (so as to convert the signal of the frequency F11 into either the input frequency F1 or the output frequency F2 of the circuit under test 1. = F1-F11 or F1 +
F11), F13 (= F2-F11 or F2 + F1
The filter 33 is configured to output the local oscillation signal of 1) in accordance with an instruction from the control unit 50, and has a band through which the signals of the frequencies F1 and F2 pass. Also,
From the above frequency relationship, the input frequency F1 and the frequency of the local oscillation signal are obtained.
Formula F12 = F1-F11, the sum frequency is F1, input frequency
The difference between the number F1 and the frequency of the local oscillation signal F12 = F1 + F11
The frequency is F1, the output frequency F2, and the frequency F1 of the local oscillation signal
3 = F2 = F2-F11, the output frequency is F2
And the frequency of the local signal F13 = F2 + F11
Becomes F2, and the filter 33 operates around the sum or difference of these.
This means that the wave number component is passed.

Then, as shown in FIG. 8, the frequency switching means 54 'sets the local oscillation signal to the frequency F13 (for example, 8.5 GHz) at the time of calibration, and outputs the signal of the frequency F2 from the output terminal 20a. And as shown in FIG.
At the time of measurement, the local oscillation signal is transmitted to the frequency F12 (for example, 7.5G).
Hz) so that a signal of the frequency F1 is output from the output terminal 20a.

In this case, at the time of calibration, the jitter generator 2
The signal of frequency F11 generated by 1 'is
0 'is converted to the frequency F2 and input to the jitter detector 35' via the output terminal 20a and the input terminal 20b. Error data is obtained in the same manner as described above.
The signal of the frequency F11 generated by the jitter generator 21 'is converted into the frequency F1 by the frequency converter 30' and input to the circuit under test 1 via the output terminal 20a, and the signal of the frequency F2 from the circuit 1 is measured. The signal is input to the jitter detector 35 'via the input terminal 20b, and the jitter transfer characteristic of the circuit under test 1 is obtained as in the above embodiment.

In the case of the jitter transfer characteristic measuring apparatus 20 ', the signal output from the jitter generating section 21' is converted into the output frequency of the circuit under test by the frequency converting section 30 'at the time of calibration, and the circuit under test is measured at the time of measurement. Is converted into an input frequency and output from the output terminal 20a, so that a signal of the same frequency is input to the jitter detector 35 'at the time of calibration and at the time of measurement. There is no need to change the operating conditions of the detection unit 35 'between calibration and measurement at all, and there is little effect on the jitter transfer characteristics of the frequency conversion unit 30'. Jitter transfer characteristics can be accurately measured.

[0062]

As described above, in the jitter transfer characteristic measuring apparatus according to the first aspect of the present invention, the frequency conversion unit is provided between the input terminal and the jitter detection unit, and the signal input to the input terminal is calibrated. And at the time of measurement, the same frequency is converted and input to the jitter detector. In the jitter transfer characteristic measuring apparatus according to claim 2 of the present invention, a frequency converter is provided between the jitter generator and the output terminal. By converting the signal output from the jitter generator to the output frequency of the circuit under test during calibration, and converting it to the input frequency of the circuit under test during measurement and outputting it from the output terminal, Thus, a signal of the same frequency is input to the jitter detector.

For this reason, the operating conditions of the jitter generating section and the jitter detecting section can be made the same at the time of calibration and at the time of measurement, and
It is possible to accurately measure the jitter transfer characteristics of the circuit under test having different input / output frequencies.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of 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 schematic diagram for explaining an operation at the time of calibration;

FIG. 5 is a schematic diagram for explaining an operation at the time of measurement.

FIG. 6 is a diagram showing measurement results.

FIG. 7 is a block diagram showing a configuration of another embodiment.

FIG. 8 is a schematic diagram for explaining an operation at the time of calibration of the embodiment of FIG. 7;

FIG. 9 is a schematic diagram for explaining an operation at the time of measurement in the embodiment of FIG. 7;

FIG. 10 is a block diagram showing the configuration of a conventional device.

DESCRIPTION OF SYMBOLS 20, 20 'Jitter transfer characteristic measuring device 20a Output terminal 20b Input terminal 21, 21' Jitter generator 22 Voltage controlled oscillator 23 Divider 24 Reference signal generator 25 Phase frequency comparator 26 Low pass filter 27 Modulated signal generator 28 Adder 30, 30 'Frequency converter 31 Local signal generator 32 Mixer 33 Filter 35, 35' Jitter detector 36 Divider 37 Voltage controlled oscillator 38 Phase frequency comparator 39 Low pass filter REFERENCE SIGNS LIST 40 Active filter 41 Jitter amount detection circuit 45 Operation unit 46 Display device 50 Control unit 51 Mode designating unit 52 Measurement starting unit 53 Jitter amount setting unit 54, 54 ′ Frequency switching unit 55 Jitter frequency variable unit 56 Jitter transmission amount calculating unit 57 Memory 58 correction means 59 display control means

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 29/02

Claims (2)

(57) [Claims] 1. A jitter transfer characteristic measuring device for measuring a transfer characteristic of a circuit under test having a difference between input and output frequencies with respect to jitter, comprising: an output terminal (20a) for inputting and outputting a signal; and an input terminal. (20b); a jitter generator (21) for phase-modulating a signal having a frequency equal to the input frequency of the circuit-under-test by a modulation signal corresponding to a predetermined amount of jitter and outputting the modulated signal from the output terminal; Frequency conversion unit (3) which mixes the signal to be transmitted with a local oscillation signal whose frequency can be switched and frequency-converts it
0), a jitter detection unit (35) for phase-detecting a signal output from the frequency conversion unit and detecting a jitter amount thereof, an operation unit (45), and the output unit according to an operation of the operation unit. Mode designating means (51) for designating either a calibration mode in which the terminal and the input terminal are directly connected or a measurement mode in which the circuit to be measured is connected between the output terminal and the input terminal. ), When the calibration mode is designated, the signal input from the jitter generator to the input terminal is converted to a predetermined frequency different from the input / output frequency of the circuit under test and input to the jitter detector, and the measurement is performed. When a mode is designated, a local oscillation signal of the frequency converter is converted so that a signal input from the circuit under test to the input terminal is converted to the predetermined frequency and input to the jitter detector. Frequency switching means (54) for switching the frequency of the jitter signal; jitter frequency varying means (55) for varying the frequency of the modulated signal of the jitter generating section within a predetermined range; A jitter transmission amount calculating means (56) for calculating a ratio of the jitter amount for each frequency of the modulation signal; and a jitter transmission amount calculation in the calibration mode in which the jitter transmission amount calculated in the measurement mode is calculated. Corrected by the amount of jitter transmission calculated by the means,
Correction means (5) for determining the jitter transfer characteristic of the circuit under test;
8) and an output means (59, 46) for outputting the jitter transfer characteristic of the circuit-under-test determined by the correction means. 2. A jitter transfer characteristic measuring device for measuring a transfer characteristic of a circuit under test having a difference between input and output frequencies with respect to jitter, comprising: an output terminal (20a) for inputting and outputting a signal; and an input terminal. (20b): a jitter generator (21 ') for phase-modulating a signal having a frequency different from the input / output frequency of the circuit under test with a modulation signal having an amplitude corresponding to a predetermined jitter amount, and outputting the jitter; A frequency conversion unit (30 ') that mixes the output signal with a local oscillation signal whose frequency can be switched, converts the frequency, and outputs a signal from the output terminal; A jitter detection unit (35 ') for detecting an amount, an operation unit (45), and a calibration mode or a previous mode in which the output terminal and the input terminal are directly connected according to the operation of the operation unit. Mode designating means (51) for designating any one of measurement modes in a state where a circuit to be measured is connected between an output terminal and an input terminal; and when a calibration mode is designated, an output signal of the jitter generating section. Is converted to a frequency equal to the output frequency of the circuit under test and output from the output terminal. When the measurement mode is designated, the output signal of the jitter generator is converted to a frequency equal to the input frequency of the circuit under test. Frequency switching means (5) for switching the frequency of the local oscillation signal of the frequency conversion unit so that the frequency is output from the output terminal.
4 ′), a jitter frequency varying means (55) for varying the frequency of the modulated signal of the jitter generation unit within a predetermined range, and the ratio of the predetermined jitter amount to the jitter amount detected by the jitter detection unit is set to Means for calculating the amount of jitter transmission calculated for each frequency of the modulation signal; and means for calculating the amount of jitter transmission calculated by the means for calculating jitter transmission in the measurement mode during the calibration mode. Corrected by the amount,
Correction means (5) for determining the jitter transfer characteristic of the circuit under test;
8) and an output means (59, 46) for outputting the jitter transfer characteristic of the circuit-under-test determined by the correction means.