Digital oscilloscope and method for displaying signal

Abstract

A measured value processing circuit records measured values for a predetermined number of repeated patterns converted by an A/D converter, in a measured value memory. A calculation section calculates standard deviations of measured values for the predetermined number of repeated patterns obtained at corresponding sample times of predetermined period. A waveform processing section uses the standard deviations determined by the calculation section to generate a waveform corresponding to the input signal. A display control section displays the waveform generated by the waveform processing section, in a display section. The present invention reduces the amount of noise displayed on a display screen. A digital oscilloscope can thus display a waveform that allows the quality of an input signal to be easily evaluated.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.

FIG. 1 is a diagram showing the configuration of an evaluation system using a digital oscilloscope 100 to which the present invention is applied;

FIG. 2 is a block diagram schematically showing the configuration of the oscilloscope 100;

FIG. 3 is a diagram of an input signal waveform displayed with a circuit board 30 in FIG. 1 powered off;

FIG. 4 is a diagram of an example in which a repeated signal waveform of binary 7-bit data output as a digital signal is sampled as an input signal Vi;

FIG. 5A is a diagram showing only an initial waveform of the repeated waveform in FIG. 4, with a time axis enlarged, and FIG. 5B is a diagram showing an example of a waveform obtained by a statistical process in accordance with a first embodiment of the present invention on the basis of the waveform in FIG. 5A;

FIG. 6 is a flowchart showing operations of the oscilloscope in accordance with the first embodiment of the present invention;

FIG. 7 is a diagram showing an example of measured values determined by sampling a waveform such as the one shown in FIG. 5A;

FIG. 8 is a diagram illustrating a process for determining a standard deviation;

FIG. 9 is a diagram showing the distribution (normal distribution curve) of sample values obtained at a sample time tn;

FIG. 10 is a diagram showing an example of two statistically processed waveforms W2 and W3 superimposedly displayed by a waveform superimposition circuit 10a; and

FIG. 11 is a diagram showing an example in which a waveform signal such as the one shown in FIG. 4 is displayed in an eye pattern.

Claims

1. A digital oscilloscope comprising: an analog to digital conversion section which samples an input signal of a repeated pattern and subjects the input signal to an analog to digital conversion;a section which records measured values for a predetermined number of repeated patterns converted by the analog to digital conversion section;a calculation section which calculates standard deviations of measured values for the predetermined number of repeated patterns obtained at corresponding sample times of predetermined period in the repeated patterns;a generation section which uses the standard deviation for each sample time determined by the calculation section to generate a waveform corresponding to the input signal; anda display section which displays the waveform generated by the generation section.

2. The digital oscilloscope according to claim 1, wherein when the standard deviation calculated by the calculation section is defined as σ, the generation section statistically processes the input signal to generate a curve indicating a waveform and having a voltage width based on σ and centered at an average value of the measured values obtained at the sample times of predetermined period in the repeated patterns.

3. The digital oscilloscope according to claim 2, wherein the display section stores the statistically processed waveform provided by the generation section and superimposedly displays two waveforms stored at different times.

4. The digital oscilloscope according to claim 2, wherein the display section has a section which displays the statistically processed waveform provided by the generation section, in an eye pattern.

5. The digital oscilloscope according to claim 2, wherein the calculation section provides a signal indicating at least two frequency distribution ranges of measured values obtained at the sample times, the generation section generates waveforms showing the two frequency distribution ranges, andthe display section displays the waveforms showing the two frequency distribution ranges, in different colors.

6. A method for displaying a signal, the method comprising: sampling an input signal of a repeated pattern and subjecting the input signal to an analog to digital conversion;recording measured values for a predetermined number of repeated patterns subjected to the analog to digital;calculating standard deviations of measured values for the predetermined number of repeated patterns obtained at corresponding sample times of predetermined period in the repeated patterns;using the standard deviation for each sample time determined by the calculation section to generate a waveform corresponding to the input signal; anddisplaying the generated waveform.

7. The method according to claim 6, wherein when the standard deviation calculated by the calculation section 9 is defined as σ, the generating the waveform includes statistically processing the input signal to generate a curve indicating a waveform and having a voltage width based on σ and centered at an average value of the measured values obtained at the predetermined sample time intervals.

8. The method according to claim 7, wherein the displaying the waveform includes storing the statistically processed waveform and superimposedly displaying two waveforms stored at different times.