JP2687914B2 - Pulse light peak time measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulsed light peak time measuring device, and more particularly to a pulsed light peak time measuring device for measuring the pulsed light peak time which is the peak of pulsed light passively received to detect the presence of a laser light source. Regarding

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional pulse light peak time measuring device of this type is provided with a photodetector element 2 for converting an incident pulsed light 1 into an electric signal and a photocurrent output by the photodetector element 2. A current-voltage conversion circuit 3 for converting the output I into a voltage and sending it as an output voltage pulse V, a peak hold circuit 7 for holding the peak value of the output voltage pulse V, an output voltage pulse V and an output of the peak hold circuit 7. And a comparison circuit 8 for comparing.

The light detecting element 2 outputs a photocurrent output I corresponding to the intensity of the incident pulsed light 1 having a substantially symmetrical waveform which passively receives the laser light emitted by the front and rear laser light sources around the peak time point on the time axis, The current-voltage conversion circuit 3 converts the photocurrent output I into an output voltage pulse V.

The peak hold circuit 7 outputs the output voltage pulse V
Holding the peak value V _P, the peak value V _P is compared with the output voltage pulse V in comparison circuit 8.

[0005] As shown in FIG. 2 (a), until the output voltage pulse V is the peak value is V> V _P, the peak hold circuit 7 holds the output voltage pulse V as the peak value in each case. When the output voltage pulse V reaches its peak, V = V _P , and the peak arrival time t _P is output as the output 10 indicating the peak time in the comparison circuit 8.

[0006]

This conventional pulsed light peak time measuring device holds the peak value of the output voltage pulse output by current-voltage conversion at the time and time corresponding to the intensity of the incident pulsed light. Since the comparison circuit 8 is configured to determine the peak time and output the peak time when the peak value is no longer updated, the intensity of the incident pulse light increases, and therefore, when the output voltage pulse is saturated,
As indicated by t _m in FIG. 2B, a time earlier than the correct peak time of the incident pulsed light in the non-saturated state of FIG. 2A is output as the peak arrival time, which is different from the actual peak time. There was a problem that it showed the peak time.

In order to solve the above-mentioned problems, the object of the present invention is to detect the pulse start time and the pulse end time of the incident pulse light, and accurately determine the peak time of the incident pulse light based on these two detection times. An object is to provide a pulsed light peak time measuring device that enables measurement.

[0008]

The present invention has the following means in order to achieve the above object. That is, the first configuration of the present invention relating to the pulsed light peak time measuring device is an electric signal of pulsed light having a symmetrical waveform around the peak time point on the time axis when passively received to detect the presence of the target laser light source. , A current-voltage conversion circuit that converts the photocurrent output into a voltage and sends it as an output voltage pulse, and a pulse start detection circuit that detects the pulse start time of the output voltage pulse And a pulse end detection circuit for detecting a pulse end time of the output voltage pulse, and a calculation circuit for calculating a peak time at which the pulsed light shows a maximum value based on the pulse start time and the pulse end time. .

According to a second aspect of the present invention, in the first configuration, the pulse start detection circuit compares the output voltage pulse with a preset reference voltage, and when the output voltage pulse exceeds the reference voltage. It is composed of a comparator whose output is inverted.

A third aspect of the present invention is the first or second aspect.
In the above configuration, the pulse end detection circuit is composed of a comparator that compares the output voltage pulse with a preset reference voltage and inverts the output when the output voltage pulse falls below the reference voltage.

In a fourth configuration of the present invention, in the first, second or third configuration, the calculation circuit starts counting at the timing of the pulse start time and ends counting at the timing of the pulse end time. The pulse light peak time calculator calculates the time between the pulse start time and the pulse end time, and the pulse light peak time calculator that halves the time measured by this counter and adds it to the pulse start time. It is composed.

[0012]

The operation of the present invention will be described below. When the pulsed laser light emitted from the target is passively received, multiple reflected waves are often included together with the direct received light, and these are received after being delayed from the direct received wave. For this reason, the direct received wave normally measures the peak value of the early arrival of the incident pulsed light, and grasps this peak value and the time at which the peak value appears as the information designating the incident pulsed light.

However, when the incident pulse light becomes large and the measurement level saturates, the saturation level shows a peak value, and the peak arrival time is measured earlier than the original pulse center time in the non-saturation state. Will be done.

In the present invention, attention is paid to the fact that the direct wave passively receiving the pulsed laser light emitted from the target has substantially front-rear symmetry with respect to the peak value on the time axis in either the unsaturated state or the saturated state. By detecting the pulse start time and the pulse end time of the voltage-converted incident pulse light and calculating the correct pulse light peak time as the central time of the incident pulse light from these two detection times, the incident pulse light is increased. Even if the measurement level becomes saturated, the correct pulse light peak time can be measured.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In this embodiment, a photodetector element 2 which converts the incident pulse light 1 received passively into an electric signal and sends it out as a photocurrent output I, and a current voltage which converts the photocurrent output I into a voltage and sends it out as an output voltage pulse V. The conversion circuit 3, the pulse start detection circuit 4 that detects the pulse start time t _S of the output voltage pulse V, and the pulse end time t of the output voltage pulse V
_It has a configuration including a pulse end detection circuit 5 for detecting _E, and a calculation circuit 6 for calculating a correct peak time at which the incident pulsed light shows the maximum value based on the pulse start time t _S and the pulse end time t _E. .

The photodetector 2 sends out a photocurrent output I according to the intensity of the incident pulsed light 1 by passive light reception, and the current-voltage conversion circuit 3 converts the photocurrent output I into an output voltage pulse V. The output voltage pulse V is input to the pulse start detection circuit 4 and the pulse end detection circuit 5.

Next, the operation of measuring the pulsed light peak time will be described by taking the output voltage pulse V as saturated as an example. As shown in FIG. 2B, the pulse start detection circuit 4 compares the output voltage pulse V with the reference level E, and considers the time point t _S when the output voltage pulse V exceeds this level as the pulse start time point. Generates a pulse start signal and outputs it to the pulse end detection circuit 5
To the calculation circuit 6. The pulse start detection circuit 4 can be realized by a comparator or the like whose output is inverted when one of the two inputs exceeds or falls below the level of the other.

The pulse end detection circuit 5 starts its operation from the pulse start time t _S output from the pulse start detection circuit 4, and the output voltage pulse V is based on the level at which the pulse start detection circuit 4 detects the appearance of a pulse. A pulse end signal is output to the calculation circuit 6 with the timing t _E below the level E as the pulse end time. Similarly to the pulse start detection circuit 4, the pulse end detection circuit 5 can also be realized by a comparator or the like.

The calculation circuit 6 calculates and outputs the pulse light peak time by the following formula 1 from the pulse start time t _S and the pulse end time t _E.

[0020]

[Formula 1] t _S + (t _E −t _S ) / 2

The calculation circuit 6 is provided with a counter and a pulsed light peak time calculator, and the counter first calculates (t _E −
t _S ). That is, the time between the pulse start time and the pulse end time is measured by the start of counting the counter by the pulse start signal and the end of the counter by the pulse end signal. Next, in the pulsed light peak time calculator, the time counted by the counter is divided into two, and the pulse start time t _S as an initial value is further divided into two minutes.
Is added to calculate the pulsed light peak time, and this is sent as the output 9.

In this way, the correct peak time t _P can be obtained even when the output voltage pulse V is saturated. The above is because the incident pulse light 1 is excessive and the output voltage pulse V
The case where the incident pulsed light 1 is not excessive and therefore the output voltage pulse V is in a non-saturated state can be calculated and output based on the above-mentioned formula 1 Is clear.

[0023]

As described above, according to the present invention, when the pulsed light of the laser emitted from the target is passively received, the characteristic that the received pulsed light has a front-back symmetry about the peak time on the time axis is used. However, the peak time of the pulsed light is calculated by calculating the peak time of the pulsed light based on the time when the pulse appears and the time when the pulse ends, even if the output of the light receiving circuit is saturated due to the intensity of the received pulsed light. There is an effect that can be accurately obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a pulsed light peak time measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of peak time calculation when the output voltage pulse V of the embodiment shown in FIG. 1 is non-saturated (in the case of (a)) and saturated (in the case of (b)).

FIG. 3 is a block diagram showing a configuration of a conventional pulsed light peak time measuring instrument.

[Explanation of symbols]

 1 incident pulsed light 2 light detecting element 3 current-voltage conversion circuit 4 pulse start detection circuit 5 pulse end detection circuit 6 calculation circuit 7 peak hold circuit 8 comparison circuit

Claims (4)

(57) [Claims] 1. A photodetection element for converting pulsed light having a symmetrical waveform back and forth around a peak point on the time axis, which is passively received to detect the presence of a target laser light source, and sending it as a photocurrent output. A current-voltage conversion circuit for converting the photocurrent output into a voltage and sending it as an output voltage pulse,
A pulse start detection circuit that detects a pulse start time of the output voltage pulse, a pulse end detection circuit that detects a pulse end time of the output voltage pulse, and the pulse light based on the pulse start time and the pulse end time. And a calculation circuit for calculating the peak time at which the maximum value is shown. 2. The pulse start detection circuit comprises a comparator that compares the output voltage pulse with a preset reference voltage and inverts the output when the output voltage pulse exceeds the reference voltage. Item 1. The pulsed light peak time measuring instrument according to Item 1. 3. The pulse end detection circuit comprises a comparator that compares an output voltage pulse with a preset reference voltage and inverts the output when the output voltage pulse falls below the reference voltage. The pulsed light peak time measuring device according to claim 1 or 2. 4. A counter, wherein the calculation circuit starts counting at the timing of the pulse start time, ends counting at the timing of the pulse end time, and counts the time between the pulse start time and the pulse end time. The pulse light peak time calculator for calculating the pulse light peak time by dividing the time counted by this counter into two and adding it to the pulse start time, and the pulse light peak time calculator according to claim 1, claim 2 or claim 3. Pulse light peak time measuring instrument.