JPH0454198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a minute time difference measuring circuit, and more specifically to a minute time difference measuring circuit that can accurately measure the time from the generation of a trigger pulse to the generation of a sampling pulse. This invention relates to a time difference measurement circuit.

(Prior Art) In a digital oscilloscope or the like, it is useful to measure a minute time difference between a trigger point and a sampling pulse when A/D converting a repetitive waveform. By measuring this minute time difference, pre-triggering (observation before the trigger point) is possible even when the equivalent sampling rate is increased by random sampling.

FIG. 7 is a diagram showing various sample modes. A indicates a real-time sample, B indicates a sequential sample, and C indicates a random sample. In each sample, the numbers on the waveform indicate the order of the sample. In the case of the real-time sample shown in A, this number is the entire number, indicating that all points are sampled when a single phenomenon occurs. On the other hand, in the case of sequential sampling shown in (b), the sampling point is shifted over time at a predetermined interval each time a repeatedly occurring phenomenon occurs, and the sample is sequentially sampled. In the case of the random sample shown in C, the position of the waveform is sampled at random as shown in the figure to detect a phenomenon that occurs repeatedly. Therefore, it can be seen that, compared to real-time sampling, random sampling allows for capturing and observing repetitive phenomena at a higher speed using an A/D converter with the same sample rate. Also, compared to a normal sampling oscilloscope, it is possible to observe phenomena before the trigger point. In order to realize such random sampling, it is necessary to measure the amount of deviation between the sampling pulse of the A/D converter and the trigger point, that is, the minute time difference.

FIG. 8 is a diagram showing an example of the configuration of a conventional minute time difference measuring device, and FIG. 9 is a timing chart showing the operation of each part. Upon receiving the input signal and the trigger control signal, the trigger generation circuit 1 generates a trigger signal as shown in FIG. 9A. This trigger signal turns off the shorting switch _SW1 of the capacitor C as shown in FIG. 9B. At this point, the switch _SW2 connected in series with the current source 2 is turned on as shown in FIG. 9E. Therefore, a constant current I is injected into the capacitor C from time _t1 when the trigger signal is generated,
The voltage Va of the capacitor C gradually increases as shown in FIG.

On the other hand, the trigger signal is also input to the D input of the first D-type flip-flop 3, and the trigger signal is input to the CLK input at the first rising edge of the sample clock of the A/D converter (time t ₂ , shown in FIG. 9). ), the D input data (in this case, level "1") is latched, and its _one output falls from "1" to "0" as shown in FIG. 9D. This _one signal turns the switch _SW2 from on to off as shown in FIG. 9(e). As a result, the injection of current I into capacitor C is stopped, and the voltage state up to this point is maintained as shown in FIG. Here, the holding voltage Va of the capacitor C is the minute time difference Δt from t ₁ to t ₂
Since it is proportional to , this voltage Va can be converted into digital data by the time difference measuring A/D converter 4 and the time difference Δt can be measured.

The A/D start signal input to the A/D converter 4 is input to the second D-type flip-flop ₅ .
given from the output. That is, the D input of the second flip-flop 5 is connected to the D input of the first flip-flop 3.
The Q ₁ output is input, and the sample clock of the A/D converter is input to the CLK input, and _{the 2} output changes from “0” to “1” at the rising edge at time t ₃ , as shown in Figure 9 (c). Turn to These _two signals are then used as A/D start signals for the A/D converter 4.

(Problems to be Solved by the Invention) In the case of the conventional device described above, the measurement accuracy of minute time differences is mainly due to the capacitor C and the switch SW ₁ ,
It depends on the characteristics of SW ₂ . Generally capacitor C
There is a leakage resistance series inductance and a series resistance, and when the minute time difference is 1 nsec or less, the series inductance becomes a large impedance and reduces measurement accuracy. Further, capacitance accuracy and stability are necessary, but it is generally extremely difficult to obtain a highly accurate and highly stable capacitor with good high frequency characteristics, and the characteristics also change over time.

Furthermore, in the case of the conventional device, when the timing of turning off switch SW ₁ and the timing of turning off switch SW ₂ conflict, a measurement error occurs due to charge injection during switching. For the above reasons, it is difficult to measure time differences with high precision using conventional devices.

The present invention has been made in view of these points, and an object thereof is to realize a minute time difference measuring device that can measure time differences with high precision.

(Means for Solving the Problems) The present invention, which solves the above problems, pulses the output of a sine wave oscillator to use it as a sample clock for an A/D converter, and also changes the phase of the output of the sine wave oscillator. A cosine wave is created by shifting the sine wave, and a trigger pulse from the trigger generation circuit is used to measure the respective amplitude values of the sine wave and cosine wave at the same time, or two amplitude values of only the sine wave at a predetermined time apart, and these measurements are performed. The present invention is characterized in that it is configured to measure a minute time difference between the trigger time and the sampling time based on the value.

(Function) A sine wave and a cosine wave are generated from the sine wave oscillator that generates the clock pulse at the same time (trigger point).
The time difference between the trigger time and the sampling time is measured from each amplitude value of the sine wave or two amplitude values of the sine wave at times separated by a predetermined time.

(Example) Hereinafter, an example of 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. In the figure, 11 is a sine wave oscillator that generates a reference sine wave, 12 is a filter that receives the output of the sine wave oscillator 11 and improves the purity of the sine wave, and 13 is a filter that receives the high purity sine wave and reaches an O level. This is a comparator that generates a sample clock for the A/D converter.

14 and 15 are buffers that receive the sine wave signal that has passed through the filter 12; 16 is a buffer that receives the output of the buffer 14; and 17 is a first buffer for time difference measurement that converts the output of the buffer 16 into digital data.
18 is a phase shifter that receives the output of the buffer 15 and shifts the phase by 90°; 19 is the phase shifter 1;
Buffer that receives the output of 8, 20 is buffer 19
This is a second A/D converter for time difference measurement that converts the output into digital data. In addition, Batsuhua 14
and 16 may be omitted. That is, these buffers 1
Since the signals passing through 4 and 16 are in the same phase, they can be omitted if consistency with subsequent circuits is not an issue.

As the phase shifter 18, for example, a delay line is used. If a day line is used,
The delay time is selected to be in phase at 90° with respect to the sine wave frequency. Therefore, since the output of the phase shifter 18 is delayed by 90 degrees, a sine wave, ie, a cosine wave, whose phase is delayed by 90 degrees is output. 21 is a trigger generation circuit that receives an input signal and a trigger control signal and generates a trigger pulse; its output is the first
(#1) and second (#2) A/D converters 17, 2
0 as the A/D start signal. The operation of the apparatus configured as described above will be explained in detail with reference to the timing chart shown in FIG.

A sine wave as shown at _f1 in FIG. 2B generated by the oscillator 11 has noise components removed by the filter 12, and then enters the comparator 13 and is compared with the O level. As a result, comparator 13
generates a sample clock for the A/D converter as shown in FIG. 2A, and this sample clock is applied as an A/D start signal to a sampling A/D converter (not shown).

On the other hand, the sine wave signal passes through the buffer 15, enters the phase shifter 18, and is delayed in phase by 90°. As a result,
If the sine wave signal is sinωt (ω; angular frequency), the output of the phase shifter 18 becomes sin(ωt−90°)=−cosωt, and a cosine wave signal is obtained. This cosine wave signal is shown at _f2 in FIG. The output of the phase shifter 18 is input to a second A/D converter 20 via a buffer 19. The sine wave signal passes through buffers 14 and 16 to the first
The signal is input to the A/D converter 17 of.

Here, assuming that the trigger pulse shown in FIG. 2C is generated from the trigger generation circuit 21 at time t, the two A/D converters 17 and 20 A/D convert the input signal at time t. and convert it into digital data. If the conversion data of the first A/D converter 17 at this time is Y, and the conversion data of the second A/D converter 20 is X, then the relationship between X, Y, and ωt is as shown in FIG. Since there is a relationship, the following equation holds true using the output of the comparator 13 as the reference time.

Y=a sin ωt...(1) X=-a cos ωt...(2) However, a=√ ² + ² Solving equations (1) and (2) for t, respectively, t=(1/ω) sin ^-1 (Y/√ ² + ² ) ...(3) t=(1/ω)cos ^-1 (-X/√ ² + ² ) ...(4) t in equation (3) or (4) is , is the very minute time difference that should be found. Therefore, by calculating the equation (3) or (4), the minute time difference can be obtained.

According to the present invention, unlike conventional devices, there is no need to inject current into a capacitor or to switch using a switch, so minute time differences can be measured with high precision. Furthermore, measurement accuracy can be improved by setting the time at which the trigger pulse is generated so that A/D conversion is performed near the full scale of the A/D converter for both X and Y, as shown in Figure 2. .

FIG. 4 is a block diagram showing another embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same numbers. In the example shown in the figure, there is only one sine wave, the trigger pulse is delayed by 90 degrees using a phase shifter, and the values at two points of the same sine wave signal are measured. This is designed to have the same effect as measuring values at the same time.

In the figure, the output (sine wave signal) of the filter 12 enters the comparator 13 and the buffer 3.
0 and enters the A/D converter 31 for time difference measurement.
On the other hand, the trigger pulse output from the trigger generation circuit 21 enters the buffer 32 and the OR gate 35. The trigger pulse output from the OR gate 35 enters the A/D converter 31 as an A/D start signal and measures the value of the sine wave signal at time t.

On the other hand, the trigger pulse that has entered the gate 32 enters the delay circuit 33 and is delayed by a time difference corresponding to 90° of ωt. This delayed trigger pulse passes through buffer 34 and enters OR gate 35. As a result, two pulses with a time difference T are output from the OR gate 35 as shown in the figure, and the A/D
It will be applied to converter 31. Time difference T
is a delay time delayed by the delay circuit 33 as described above, and is a time difference corresponding to 90° of ωt. The first pulse measures the value of the sinusoidal signal at time t, and the next pulse measures the value of the sinusoidal signal after time T. The value of the sine wave signal after T is the same as the value of the cosine wave signal at time t, so if the first measurement value is Y and the next measurement value is X, (3), (4) The formula can be applied as is. In this way, in the embodiment shown in FIG. 4, the number of A/D converters can be reduced to one.

Furthermore, even if the delay of 90° is 270°, 450°, etc., equations (3) and (4) can be applied as they are based on the same principle.

When realizing a digital oscilloscope, as shown in Figure 5, the analog input is converted to a high-speed sample rate by using multiple sample and hold circuits and an A/D converter using sequential pulses. There are known methods for obtaining .
When such a configuration is used, the minute time difference measuring device shown in FIG. The converter can be omitted.

FIG. 6 is a block diagram showing another embodiment of the present invention based on this idea. Fourth
Components that are the same as those in the figures are designated by the same reference numerals. The sine wave signal that has passed through the filter 12 is applied via a buffer 41 to each channel input of the high-speed sample rate circuit. By switching the switch, either the analog input or the sine wave signal is input to the sample and hold circuit. The two trigger pulses output from the OR gate 35 enter the control circuit 42 on the high sample rate circuit side.
The control circuit 42 searches for an empty channel and
Put a sine wave signal into the empty channel and obtain two sine wave signal measurements.

(Effects of the Invention) As explained in detail above, according to the present invention,
A sine wave and a cosine wave are generated from a sine wave oscillator that generates clock pulses for the sample rate, and the sample clock rises by measuring the time difference between the trigger time and the sampling time from the values of the sine wave and cosine wave at the same time (trigger point). It is possible to realize a minute time difference measuring device that can measure a minute time difference between the time and the trigger point with high precision. According to the present invention, since the method of measuring the minute time difference by measuring the amount of current injected into the capacitor is not used, it is not affected by the capacitor or switch, and is completely free from the influence of fluctuations in the amplitude of the sine wave signal. I don't accept it.

[Brief explanation of the drawing]

Fig. 1 is a configuration block diagram showing one embodiment of the present invention, Fig. 2 is a timing chart showing the operation of each part, Fig. 3 is an explanatory diagram during X, Y measurement, and Fig. 4 is another example of the present invention. FIG. 5 is a configuration block diagram showing an embodiment, FIG. 5 is a configuration diagram of a sample rate circuit, FIG. 6 is a configuration block diagram showing another embodiment of the present invention, FIG. 7 is a diagram showing various sample modes, and FIG. The figure is a configuration block diagram of a conventional device, and FIG. 9 is a timing chart showing the operation of each part. 1, 21... Trigger generation circuit, 2... Constant current source, 3, 5... Flip-flop, 4, 17, 2
0, 31... A/D converter, 11... Oscillator, 1
2...Filter, 13...Comparator, 14~
16, 19, 30, 32, 34, 41... Buffer, 18... Phase shifter, 33... Delay circuit, 3
5...OR gate, 42...control circuit, SW ₁ ,
SW ₂ ...Switch.

Claims (1)

[Claims] 1. A trigger pulse generation circuit that detects a trigger event that occurs asynchronously, a sine wave signal oscillator that generates a sine wave signal with a frequency f that is a reference for measuring the timing of occurrence of this trigger event, A reference clock generator generates a reference clock by comparing the output of the sine wave signal oscillator with a zero level, and the output pulse of the trigger pulse generation circuit corresponds to a phase angle of 90 degrees of the output frequency f of the sine wave signal oscillator. a delay circuit for delaying the time, the output pulse of the trigger pulse generation circuit is given as a sampling signal to A/D convert the value of the output Y of the sine wave signal oscillator, and the output pulse of the delay circuit is given as a sampling signal. an A/D that converts the output X of the sine wave signal oscillator into A/D;
converter and calculation means for calculating the time difference t between the trigger event occurrence timing and the reference clock by calculating the following formula based on the Y and X digital data obtained from the A/D converter. A minute time difference measurement device equipped with t=(1/ω)sin ^-1 (Y/√ ² + ² ) or t=(1/ω)cos ^-1 (-X/√ ² + ² )