JP2011038786A - Waveform display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveform display capable of detecting a propagation delay difference without effect of frequency characteristics or noise of a signal path including an input means such as a probe, and to automatically correct a skew among measurement channels. <P>SOLUTION: In the waveform display including a plurality of measurement channels, a skew correction means is provided, which automatically corrects the skew among the measurement channels on the basis of an amplitude of a common sine wave signal measured by each measurement channel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a waveform display device, and more particularly to correction of skew (time difference) between measurement channels.

  A digital oscilloscope, which is a type of waveform display device, converts an analog input signal into digital data using an A / D converter and stores it in a data memory as waveform data. It is configured to perform a corresponding calculation process and display these waveform data and calculation results on a raster scan type display unit.

  In general, a digital oscilloscope is provided with a plurality of measurement channels so that signals of a plurality of systems can be measured simultaneously, and measurement is performed by connecting probes to these measurement channels. Here, when focusing on the frequency band characteristics in the input path of each measurement channel, there are many differences.

  FIG. 3 is an explanatory diagram showing a conventional skew measurement example using a digital oscilloscope. In FIG. 3, A / D converters 3a and 3b are connected to an output terminal of a signal source 1 that outputs a square wave, for example, via signal paths 2a and 2b including probes.

  The digital signals converted by the A / D converters 3 a and 3 b are input to the data processing unit 4, subjected to necessary data processing, and then input to the display processing unit 5.

  The display processing unit 5 executes processing for displaying the data processing result input from the data processing unit 4 in a desired display form, and inputs the processing result to the display unit 6 for display.

  FIG. 4 is a display example diagram in the configuration of FIG. 3, (A) shows a case where the frequency band characteristics of the measurement channel are the same, and (B) shows a case where the frequency band characteristics of the measurement channel are different.

  When the frequency band characteristics of the measurement channels are the same, the rise time or fall time of the square wave measured in each measurement channel is also equal. Therefore, if it is within the range of the H / L level of the waveform, as shown in (A), the time difference at the point where the same arbitrary voltage level (for example, 50%) in the waveforms W1, W2 is crossed is determined as the propagation delay difference tpd. Can be detected as

  On the other hand, when the frequency band characteristics of the measurement channels are different, the rise time or the fall time of the square wave measured in each measurement channel is also different. Therefore, as shown in (B), a change point where the voltage levels of the waveforms W1 and W2 start rising from zero is extracted, and a time difference between these change points is detected as a propagation delay difference tpd.

Tech-On! “Introduction to the Use of Digital Oscilloscopes 5th Power Circuit and Digital Oscillo” [online], September 26, 2007, Nippon Tektronix, [Search March 2, 2009], Internet <URL: http: // techon. nikkeibp.co.jp/article/NEWS/20070916/139208/>

  Non-Patent Document 1 describes a method for measuring characteristics of a power MOS FET used as a switching device of a switching power supply.

  6 of Non-Patent Document 1 shows an example of two signals including skew, and FIG. 7 of Non-Patent Document 1 shows an example of two signals corrected by deskew.

  However, the signal change point as shown in FIG. 4B is easily affected by noise, and it is difficult to accurately detect the propagation delay difference tpd.

  The present invention solves such problems, and its purpose is to detect a propagation delay difference without being affected by frequency characteristics or noise of a signal path including an input means such as a probe, and between measurement channels. An object of the present invention is to provide a waveform display device capable of automatically correcting skew.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In a waveform display device having a plurality of measurement channels,
A skew correction means is provided for automatically correcting the skew between the measurement channels based on the amplitude of the common sine wave signal measured in each measurement channel.

The invention according to claim 2 is the waveform display device according to claim 1,
The skew correction means includes
The apparatus further comprises means for normalizing the measurement signal of each measurement channel.

The invention according to claim 3 is the waveform display device according to claim 1 or 2,
The skew correction means includes
A comparison circuit for comparing the amplitude of a common sine wave signal measured in each measurement channel, and the comparison result of the comparison circuit is reflected in a reference voltage of an A / D converter provided in each measurement channel; Thus, the output signals of these A / D converters are normalized.

The invention according to claim 4 is the waveform display device according to any one of claims 1 to 3,
The skew correction means includes
The skew is automatically corrected by combining arbitrary measurement channels of the plurality of measurement channels.

The invention according to claim 5 is the waveform display device according to any one of claims 1 to 4,
The automatic skew correction function by the skew correction means is selectively turned on / off.

  According to the present invention, there is provided a waveform display device capable of detecting a propagation delay difference without being affected by frequency characteristics and noise of a signal path including an input means such as a probe and automatically correcting a skew between measurement channels with high accuracy. can get.

It is a block diagram which shows one Example of this invention. It is a block diagram which shows the other Example of this invention. It is explanatory drawing which shows the example of the conventional skew measurement. It is a display example figure in the structure of FIG.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. The difference between FIG. 1 and FIG. 3 is the specific configuration of the output signal of the signal source 1 and the data processing unit 4.

  That is, the signal source 1 in FIG. 1 outputs a sine wave signal. This sine wave signal is input to A / D converters 3a and 3b via signal paths 2a and 2b including probes, for example, and converted into digital signals.

  The digital signal converted and output from the A / D converter 3a is input to the first effective value conversion circuit 4a and converted into the first effective value signal 1, and the first effective value signal 1 is the first normal value signal. And is normalized to 1 / √2 of the first normalized signal 1. The first normalized signal 1 normalized by the first normalization circuit 4b is input to one input terminal of the first subtractor 4c and to one input terminal of the second subtractor 4d. Entered.

  On the other hand, the digital signal converted and output from the A / D converter 3b is input to the second effective value conversion circuit 4e to be converted into the second effective value signal 2, and the second effective value signal 2 is the second effective value signal 2. Is normalized to a second normalized signal 2 of 1 / √2. The second normalized signal 2 normalized by the second normalization circuit 4f is input to the other input terminal of the first subtractor 4c, and the second subtraction is performed via the N sample delay circuit 4g. Is input to the other input terminal of the device 4d.

  The output signal of the first subtractor 4c is input to the third effective value conversion circuit 4h and converted into the third effective value signal 3, and this third effective value signal 3 is output from the delay advance / delay determination circuit 4i. The signal is input to one input terminal and also input to one input terminal of the delay difference detection circuit 4j. The absolute value of the delay difference can be detected from the third effective value signal 3.

  The output signal of the second subtractor 4d is input to the fourth effective value conversion circuit 4k and converted into the fourth effective value signal 4, and this fourth effective value signal 4 is output from the delay advance / delay determination circuit 4i. Input to the other input terminal.

  The output signal of the delay advance / delay determination circuit 4i is input to the other input terminal of the delay difference detection circuit 4j. The output signal of the delay difference detection circuit 4j is input to the display processing unit 5.

  In FIG. 1, the sinusoidal signal output from the signal source 1 is defined as sin ωt, and the signals input to the A / D converters 3a and 3b through the signal paths 2a and 2b and converted into digital signals are respectively asin ωt and Bsin. Let (ωt + θ). Here, the amplitudes A and B have different values depending on the frequency band difference between the signal paths 2a and 2b, and θ is the phase difference between the signals passing through the two signal paths 2a and 2b.

  The first effective value conversion circuit 4a and the second effective value conversion circuit 4e calculate the effective values A / √2, B / √2 of the respective signals, and the first normalization circuit 4b and the second normalization. The circuit 4f normalizes them to 1 / √2, and then subtracts them using the first subtractor 4c and the second subtractor 4d.

When transforming these subtractions using the trigonometric formula shown in Equation 1,
sin α + sin β = 2 × sin ((α + β) / 2) × cos ((α−β) / 2) (1)
Equation 2 as shown below is obtained.
sinωt−sin (ωt + θ) = − 2 × sin (θ / 2) × cos (ωt + θ / 2) (2)

  The third effective value conversion circuit 4 h obtains the effective value of the output signal of the first subtractor 4 c as the third effective value signal 3, and the fourth effective value conversion circuit 4 k obtains the fourth effective value signal 4 as the fourth effective value signal 4. The effective value of the output signal of the subtracter 4d of 2 is obtained.

  Based on the third effective value signal 3 and the fourth effective value signal 4 thus obtained, the absolute value of the delay difference can be obtained.

That is, when the effective value of the signal expressed by Expression 2 is Vrms, it can be expressed by Expression 3 as shown below.
Vrms = 2 × sin (θ / 2) / √2 (3)

From Equation 3, the phase difference θ is
θ = 2 × sin ⁻¹ (√2 × Vrms / 2) (4)
(| Θ | <= π / 2)
And the absolute value of the delay difference is
| t | = θ / ω (5)
It becomes.

  As a result, when detecting the delay difference, the skew between the measurement channels can be measured easily and accurately without being affected by the frequency characteristics and noise of the input means such as the probe and the signal path. Automatic correction can be performed.

  In addition, since the necessary calculation function is already incorporated in the waveform measuring apparatus, it is not necessary to add the calculation function again.

  FIG. 2 is a block diagram showing another embodiment of the present invention, and the same reference numerals are given to portions common to FIG. In the example of FIG. 2, instead of the normalization circuits 4b and 4f of FIG. 1, the first effective value signal 1 and the second effective value signal 2 are compared, and the comparison results are A / D converters 3a and 3b. A comparison circuit 4m for reflecting the reference voltage is provided.

  That is, the A / D converters 3a and 3b have a normalization function that can be normalized to a desired output value by adjusting the reference voltage. Therefore, in the configuration of FIG. 2, the comparison circuit 4m compares the first effective value signal 1 and the second effective value signal 2 and reflects the comparison result in the reference voltages of the A / D converters 3a and 3b. Thus, normalization of the first effective value signal 1 and the second effective value signal 2 is realized.

  In the above embodiment, an example of a digital oscilloscope has been described. However, the present invention can also be applied to other waveform measurement apparatuses having a plurality of measurement channels such as a time measurement apparatus.

  In addition, by combining arbitrary measurement channels of a plurality of measurement channels so as to automatically correct the skew, or by selectively turning on / off the skew automatic correction function by the skew correction means, Diversification of the measurement function of the waveform display device can be achieved.

  As described above, according to the present invention, the propagation delay difference can be detected without being affected by the frequency characteristics and noise of the signal path including the input means such as the probe, and the skew between the measurement channels can be automatically and accurately detected. A waveform display device capable of correction can be realized.

DESCRIPTION OF SYMBOLS 1 Signal source 2a, 2b Signal path | route 3a, 3b A / D converter 4 Data processing part 4a 1st effective value conversion circuit 4b 1st normalization circuit 4c 1st subtractor 4d 2nd subtractor 4e 2nd Effective value conversion circuit 4f second normalization circuit 4g N sample delay circuit 4h third effective value conversion circuit 4i delay advance / delay determination circuit 4j delay difference detection circuit 4k fourth effective value conversion circuit 4m comparison circuit 5 display Processing unit 6 Display

Claims (5)

In a waveform display device having a plurality of measurement channels,
A waveform display device comprising skew correction means for automatically correcting a skew between the measurement channels based on an amplitude of a common sine wave signal measured in each measurement channel. The skew correction means includes
2. The waveform display device according to claim 1, further comprising means for normalizing a measurement signal of each measurement channel. The skew correction means includes
A comparison circuit for comparing the amplitude of a common sine wave signal measured in each measurement channel, and the comparison result of the comparison circuit is reflected in a reference voltage of an A / D converter provided in each measurement channel; 3. The waveform display apparatus according to claim 1, wherein the output signals of these A / D converters are normalized. The skew correction means includes
The waveform display apparatus according to claim 1, wherein a skew is automatically corrected by combining arbitrary measurement channels of the plurality of measurement channels.   5. The waveform display device according to claim 1, wherein the automatic skew correction function by the skew correction unit is selectively turned on / off.

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