JP2917942B2 - Pulse light time interval measurement method and pulse light time interval measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse light time interval measuring method and a pulse light time interval measuring method for measuring the time interval between two pulse light signals continuously observed at the same period with high accuracy.

[0002]

2. Description of the Related Art This pulse light time interval measurement method is used for, for example, a laser measuring instrument, and uses light as a carrier wave.
The time interval between pulse signals of transmitted and received light (however, those continuously observed at the same period) is measured. In the conventional general pulsed light time interval measurement method, a trigger signal is generated by any method from each of two observed pulsed light signals, and the time interval between these trigger signals is determined by an electronic circuit such as a counter. It was measured directly.

[0003]

As described above, in the conventional pulsed light time interval measurement method in which the time interval between trigger signals is directly measured by an electronic circuit, a high-speed time interval measurement is performed in order to perform a highly accurate time interval measurement. In addition, a high-precision electronic circuit is required, which is very expensive.

[0004] In addition, there are the following problems in increasing the precision.

In general, when measuring the time interval of a pulse signal of a high repetition pulse laser beam having a pulse width of several ns to several tens of ns and a maximum repetition frequency of several tens of kHz with a high accuracy of 100 ps or less, 100 MHz or more is required. And an ultra-high-speed counter corresponding to 10 GHz or more are required, but it is difficult to realize such an ultra-high-speed electronic circuit due to the performance limit of an electronic device.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to increase the time interval of a pulse signal of a high repetition pulse laser beam having a pulse width of several ns to several tens ns and a maximum repetition frequency of several tens of kHz. An object of the present invention is to provide a pulse light time interval measurement method and a pulse light time interval measurement method with a simple and inexpensive device configuration that can measure with a high accuracy of the order of 10 ps.

[0007]

In order to achieve the above-mentioned object, the present invention provides a pulse for measuring a time interval which is a phase difference between first and second pulsed optical signals continuously observed at the same period. In the optical time interval measurement method, the first and second pulsed optical signals are represented by T
A / D conversion is performed at the cycle of [T + Δt] (T >> Δt) and the first
And an A / D converter for obtaining a second digital pulse signal, and a time difference between the first and second digital pulse signals
The correlation function of τ is obtained, and the maximum correlation value Φ of the obtained correlation function is obtained.
(Τ _max ) and the time difference τ _max that gives it,
The correlation values before and after the said maximum correlation value _{Φ (τ max) Φ (τ} max
+1) and Φ (τ _max -1), and a time interval T between the first and second pulsed light signals.
and a time interval calculating means for calculating m using the following equation . Tm = Δt × {τ _max + [Φ (τ _max +1) −Φ (τ _max −1)] / 2 [2Φ (τ _max ) −Φ (τ _max +1) −Φ (τ _max −1)]}

[0008]

[0009]

The pulse light time interval measuring method according to the present invention includes
First and second pulses continuously observed at a new cycle
Optical signalIs the phase difference betweenFor pulsed light to measure time intervals
In the interval measuring method, the first and second pulses
Light signalLet T be the period of these signals[T + Δt] (T
>> Δt) A / D conversion at the period of 1st and 2nd digital
Tal pulse signal, The first and second digital paths
The correlation function of the time difference τ of the
Maximum correlation value Φ (τ_max) And the time difference τ that gives it_max
CalculateWith, The calculated maximum correlation value Φ (τ
_max) Before and after Φ (τ_max+1), Φ (τ_max−
1) Time of the first and second pulsed optical signals
The interval Tm is calculated using the following equationThatFeatures
You. Tm = Δt × ｛τ_max+ [Φ (τ_max+1) -Φ (τ_max-1)] / 2 [2Φ (τ_max) -Φ (τ_max+1) -Φ (τ_max-1)]｝

According to the present invention as described above, the first and second pulsed optical signals continuously observed at the same period have a period ([T + Δt] (T >> Δ) where aliasing occurs.
Since the A / D conversion is performed in t)) , the first and second digital pulse signals obtained by the A / D conversion completely have a relative relationship such as the amplitude and the phase of the pulse light signal before the conversion. The low-speed signal is composed of the stored low-frequency components. Specifically, it is a low-speed signal composed of low frequency components as shown in FIG. 2 described in an embodiment described later. As described above, since the first and second digital pulse signals are low-speed signals composed of low-frequency components, the cross-correlation of these signals can be calculated with high accuracy. Since the second digital pulse signal completely preserves the relative relationship such as the amplitude and phase of the original pulse light signal, the obtained correlation value matches the correlation value of the original pulse light signal. I do. Therefore, the time interval between the original first and second pulsed light signals can be measured from the correlation value obtained from the first and second digital pulse signals.

More specifically, in the present invention ,
Means that the first and second digital pulse signals are in the time axis direction
Is enlarged by T / Δt times. That is, Δt /
It becomes a low-speed signal composed of a low frequency component multiplied by T. Ma
Further, in the present invention, the maximum correlation value Φ (τ _max ) of the first and second digital pulse signals and the correlation values Φ before and after the maximum correlation value Φ (τ _max )
The time interval Tm is calculated from (τ _max +1) and Φ (τ _max -1) . Therefore, in the present invention, the time interval Tm is not simply obtained from the maximum correlation value Φ (τ _max ), but the preceding and following correlation values Φ (τ _max +1), Φ (τ _max -1)
Time interval Tm in a state containing becomes that are calculated,
The calculation accuracy of the time interval Tm is higher.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings.

The pulse light time interval measuring method according to the present invention is used for a laser measuring device such as a laser distance measuring device or a relative speed detecting device for measuring a distance using a laser beam. Is a carrier wave, and the time interval between pulse signals of transmitted and received light (however, those that are continuously observed at the same period) is measured with high accuracy.

FIG. 1 is a block diagram showing the main components of a pulse light time interval measuring method according to one embodiment of the present invention. In FIG. 1, the main components of the pulse light time interval measurement method include an A / D converter 3, a correlator 6, and a time interval calculation unit 8.

As shown in FIG. 2, the A / D converter 3 outputs a pulse light signal A (t) continuously observed at the same period T.
1 and the pulse light signal B (t) 2 as inputs, respectively.
The digital pulse signal A (n) 4 and the digital pulse signal B (n) 5 are A / D-converted at a cycle of [T + Δt] (T >> Δt). In the A / D conversion in the A / D converter 3, the original pulse light signal A (t) 1 and the pulse light signal B (t) 2 maintain the relative relationship between the amplitude and the phase of each. The digital pulse signal A (n) composed of low frequency components equal to or less than 1/2 (T + Δt) due to the aliasing effect.
4 and a digital pulse signal B (n) 5 (see FIG. 2). When this conversion is viewed in the time domain, it has been converted to a signal multiplied by T / Δt in the time axis direction.

The correlator 6 receives the digital pulse signal A (n) 4 and the digital pulse signal B (n) 5 converted by the A / D converter 3 as inputs, and cross-correlates them (separated by a time interval τ). The strength of the relationship between the two signals at that time). That is, the digital pulse signal A
A function Φ (τ) corresponding to the time difference τ between (n) 4 and the digital pulse signal B (n) 5 is obtained by the following equation.

[0018]

(Equation 1) Then, the maximum value of the obtained function Φ (τ), that is, the maximum value of the discrete-time cross-correlation function of the input digital pulse signal A (n) 4 and digital pulse signal B (n) 5, and the time difference τ giving the maximum value calculating the _max, the correlation value of the calculated maximum correlation value [Phi and (τ _{m ax)} before and after Φ (τ _max +
1) and Φ (τ _max -1) are output.

The time interval calculator 8 calculates the maximum correlation value Φ (τ _max ) output from the correlator 6, the correlation value Φ (τ _max +1),
Observed pulse light signal A (t) 1 and pulse light signal B (t) 2 using the following equation based on Φ (τ _max -1)
Is calculated.

Tm = Δt × ｛τ _max + [Φ (τ _max +1)
−Φ (τ _max −1)] / 2 [2Φ (τ _max ) −Φ (τ _max
+1) -Φ (τ _max -1)]｝ (1) In the calculation of the time interval Tm using the above equation (1), for example, as shown in FIG. 3, the digital pulse signals A (n), B
When the discrete-time correlation function (n) (indicated by a cross in the figure) gives the maximum correlation value Φ (τ) with the time difference τ “4 ns”, the maximum correlation at the time difference τ _max (= 4 ns) The time Φ (τ _max ) and the correlation value Φ (τ _max +1) and correlation value Φ (τ _max -1) of the time difference τ _max +1 (= 5 ns) and the time difference τ _max -1 (= 3 ns), respectively. The interval Tm is given.

[0021]

Here, a high repetition pulse laser beam having a pulse width of several ns to several tens ns and a maximum repetition frequency of several tens of kHz is used as a carrier wave, and the time interval between pulse signals of the transmitted and received light is measured. The case will be described as an example.

For example, a pulse width of 10 ns and a repetition rate of 10 ns
In the case of a pulsed optical signal of kHz, if the conversion frequency of the A / D converter 3 is 9.9999 kHz (Δt = 1 ns) and the time interval between two observed pulsed optical signals is 1 μs, about ｛1 μs / [ (1/10 kHz)-1 / 9.99
99 kHz)]｝ ≒ 1000 samples, ie 0.1
By measuring the seconds, a digital signal in which the relative amplitude / phase information of the two pulse signals to be measured is accurately stored can be obtained.

Next, since Δt = 1 ns, in the correlator 6, the time difference τ _max giving the maximum value of the discrete-time cross-correlation function of these digital signals is ± 500 ps (± Δt / 2).
It is required with the precision of. In the time interval calculation section 8, the correlator 6
Using the above-described equation (1) from the maximum correlation value obtained in step (1) and the correlation values before and after the maximum correlation value, the time interval T can be extremely high accuracy of 10 ps or less, although it depends on the S / N of the original pulse light signal.
m is required.

[0024]

According to the present invention constructed as described above, an A / D converter and an arithmetic unit comprising simple and inexpensive hardware and software are used for measuring the time interval. Since such an electronic circuit such as a counter is not required, high accuracy can be realized with a simple and inexpensive device configuration.

Also, the observed pulse light signal is temporarily converted into a low-speed digital signal composed of low frequency components by utilizing the aliasing effect, and the time of the original pulse light signal is calculated from the correlation value obtained from these digital pulse signals. Since the interval is measured, a high time resolution of the order of 10 ps, which has been conventionally difficult to realize, can be easily realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing main components of a pulse light time interval measurement method according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an aliasing effect in the A / D converter 3 shown in FIG.

FIG. 3 shows original pulse light signals A (t) and B (t) based on discrete time correlation functions of digital pulse signals A (n) and B (n).
FIG. 5 is a diagram for explaining a method of calculating a time interval Tm of the first embodiment.

[Explanation of symbols]

 Reference Signs List 1 pulse light signal A (t) 2 pulse light signal B (t) 3 A / D converter 4 digital pulse signal A (n) 5 digital pulse signal B (n) 6 correlator 8 time interval calculator

Continuation of front page (56) References JP-A-4-164280 (JP, A) JP-A-7-280542 (JP, A) JP-A-5-346421 (JP, A) JP-A-1-129183 (JP) JP-A-62-165176 (JP, A) Patent No. 2573682 (JP, B2) Utility model registration 1899119 (JP, Y2) JP-B-60-30902 (JP, B2) (58) Fields investigated (Int. Cl ^6, DB name) G01S 7/48 -. 7/50 G01S 17/00 - 17/95

Claims (2)

(57) [Claims] 1. A pulse light time interval measurement method for measuring a time interval which is a phase difference between first and second pulse light signals continuously observed at the same period, wherein the first and second pulses are period of the optical signal these signals
A is obtained by performing A / D conversion with a period of [T + Δt] (T >> Δt) as T to obtain first and second digital pulse signals.
D converter, and a correlation function of a time difference τ between the first and second digital pulse signals is obtained, and a maximum correlation value Φ (τ) of the obtained correlation function is obtained.
_max ) and the time difference τ _max that gives it ,
The correlation value Φ (τ _max + ) before and after the _maximum correlation value Φ (τ _max )
1), a correlation function calculating means for calculating Φ (τ _max -1), and a time interval Tm between the first and second pulsed light signals.
A pulse light time interval measuring method, comprising: a time interval calculating means for calculating using the following equation . Tm = Δt × {τ _max + [Φ (τ _max +1) −Φ (τ _max −1)] / 2 [2Φ (τ _max ) −Φ (τ _max +1) −Φ (τ _max −1)]} 2. The method according to claim 1, wherein the first and second samples are continuously observed at the same period.
A time interval that is a phase difference between the second pulsed optical signal and the second pulsed optical signal.
In the pulsed light time interval measuring method for measuring, the first and second pulsed light signals are subjected to a cycle of these signals.
Where T is the A / D conversion at a period of [T + Δt] (T >> Δt).
In this way, the first and second digital pulse signals are obtained, and the time difference τ between the first and second digital pulse signals is calculated.
A correlation function is obtained, and the maximum correlation value Φ (τ
_max ) and the time difference τ _max that gives it ,
Correlation values before and after the calculated maximum correlation value Φ (τ _max )
Φ (τ _max +1) and Φ (τ _max -1) are obtained, and the time interval Tm between the first and second pulsed light signals is calculated as follows.
Pulse light time characterized by being calculated using the following equation
Interval measurement method. Tm = Δt × {τ _max + [Φ (τ _max +1) −Φ (τ _max −1)] / 2 [2Φ (τ _max ) −Φ (τ _max +1) −Φ (τ _max −1)]}