JP3779633B2 - Pulse signal generation circuit and distance measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pulse signal generation circuit that generates a pulse signal corresponding to an input signal, and a distance measurement device that uses the pulse signal generation circuit to measure a distance to a measurement object using light.
[0002]
[Prior art]
A distance measuring device used for a general surveying instrument needs to measure a distance in a range of 1 m to several km with high accuracy of accuracy 5 mm + 3 ppm × D (D is a distance to be measured). A variation in the received signal amplitude is a factor that degrades the accuracy. As a method for absorbing this fluctuation, there is signal detection by a differentiation circuit. When the pulsed received signal is passed through a differentiating circuit with optimized constants, an output signal whose sign is inverted at the timing of the peak of the pulse is obtained. Since the timing of the peak position does not change even if the amplitude of the pulse changes, it is possible to detect the timing with little influence by the amplitude fluctuation by detecting the zero cross of the output of the differentiation circuit.
[0003]
[Problems to be solved by the invention]
However, it is difficult to optimize the constants of the differentiating circuit in this method using a differentiating circuit, and even if one device is optimized, there is an individual difference in pulse width depending on the device, so the total number is optimized with the same constant. There is a problem that the influence of timing deviation due to amplitude fluctuation becomes large.
[0004]
The present invention provides a pulse signal generation circuit in which the timing of the pulse signal to be generated is not affected by fluctuations in the amplitude of the input signal, and also provides a distance measurement device that enables highly accurate distance measurement.
[0005]
[Means for Solving the Problems]
The first aspect of the present invention is applied to a pulse signal generation circuit that generates a pulse signal corresponding to an input signal, and the input signal is delayed by a first time that is a value within the signal width of the input signal. A first delay means for outputting a signal, and a second delay signal for outputting a second delayed signal by delaying the input signal by a second time that is a value within twice the signal width of the input signal and longer than the first time. Based on the two delay means, the input signal, the first delay signal, and the second delay signal, the intersection of the output levels of the input signal and the first delay signal is detected to generate the front edge of the pulse signal And an intersection detection means for detecting the intersection of the output levels of the first delay signal and the second delay signal to generate the rear edge of the pulse signal to generate the pulse signal.
According to a second aspect of the present invention, in the pulse signal generation circuit according to the first aspect, the intersection detection means outputs the first signal as active when detecting that the input signal is equal to or higher than a predetermined level. Comparator means and enabled when the first signal becomes active, outputs the second signal as active when enabled and when the level of the input signal is lower than the level of the first delay signal Second comparator means and enabled when the second signal becomes active, and when enabled and when the level of the first delay signal is higher than the level of the second delay signal A third comparator that inverts and outputs the third signal when the signal is active and the level of the first delay signal is lower than the level of the second delay signal; With the door, in which the third signal a third comparator means outputs a pulse signal.
According to a third aspect of the present invention, in the pulse signal generation circuit according to the first or second aspect, the first time corresponds to a pulse width at a value about half the amplitude of the input signal, and the second time is the amplitude of the input signal. This is equivalent to about twice the pulse width at about half the value.
According to a fourth aspect of the present invention, in the pulse signal generation circuit according to any one of the first to third aspects, the intersection detection means uses an ECL element, and the pulse signal output from the ECL element is changed from the ECL level to the TTL level. Further, it is provided with a conversion means for converting to.
According to a fifth aspect of the present invention, a light transmitting means for transmitting the distance measurement light toward the target based on the distance measurement command signal, and a distance measurement light reflected by the target are received and a light reception signal is output. The light receiving means, the time measurement end signal generating means for generating a time measurement end signal based on the light reception signal, the time measurement is started based on the distance measurement command signal, the time measurement is ended based on the time measurement end signal, and the light transmission is started. Distance provided with time measuring means for measuring the light travel time until light reception, and calculation means for obtaining the light travel time measured by the time measurement means and calculating the distance to the target based on the obtained light travel time The time measurement end signal generation means applied to the measurement apparatus includes the pulse signal generation circuit according to any one of claims 1 to 4, wherein the input signal of the pulse signal generation circuit corresponds to the received light signal, and the pulse signal generation Circuit pulse No. are those corresponding to a time measurement end signal.
The invention according to claim 6 includes the distance measuring device according to claim 5.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a distance measuring apparatus according to an embodiment of the present invention. The distance measuring apparatus according to the present embodiment measures the distance to a measurement object (target object) using pulsed light. This distance measuring device is particularly provided in a surveying instrument that measures the distance to the measurement object, the angle in the direction of the measurement object, and the like.
[0007]
The arithmetic control unit 1 composed of a CPU or the like gives a distance measurement command signal S101 to the time measurement unit 2 in accordance with a measurement command signal from an operator or the like. The time measuring unit 2 gives a pulse emission command S102 to the light transmitting unit 3 and starts measuring time. The time measuring unit 2 includes a counter that counts the reference clock from the start to the end of time measurement, and an integration circuit (not shown) that interpolates and calculates the time between the reference clocks. The integration circuit outputs a voltage signal corresponding to the elapsed time between the reference clocks. Precise time is measured by a combination of these counters and an integration circuit.
[0008]
The light transmission unit 3 includes, for example, a semiconductor laser drive circuit 31, a semiconductor laser 32, and a light transmission optical system 33 that transmits the emitted pulsed light 103. In the light transmission optical system 33, an optical path splitting unit 34 that splits the pulsed light 103 into a distance measuring optical path 110 that is an external optical path and a reference optical path 111 that is an internal optical path is provided. The optical path splitting unit 34 is provided with, for example, an optical path splitting unit 34 configured by a semi-transmissive mirror disposed at 45 ° in the incident optical path of the pulsed light 103. Accordingly, the pulsed light 103 is divided into a pulsed light 104 emitted to the distance measuring optical path 110 and a pulsed light 105 emitted to the reference optical path 111.
[0009]
Further, the light transmission optical system 33 is provided with an optical path switching unit 36, and either the distance measuring optical path 110 or the reference optical path 111 is shielded by a switching signal (not shown) from the arithmetic control unit 1. When the reference optical path 111 is shielded and pulsed light is projected from the distance measuring light path 110, the reflected pulsed light 106 reflected by the measurement object and returned from the distance measuring light path 110 is received by the light receiving optical in the light receiving unit 4. The light enters the system 41a. The pulsed light 106 incident on the light receiving optical system 41a is condensed on a light receiving element 42 such as an APD (avalanche photodiode) via the light amount adjusting filter 44 and the light receiving optical system 41b, and is subjected to photoelectric conversion.
[0010]
On the other hand, when the distance measuring optical path 110 is blocked, the reference pulse light 105 is transmitted to the reference optical path 111, the light amount is attenuated to a predetermined level by the neutral density filter 35, and the light receiving unit is passed through the light amount adjustment filter 44. 4 to the light receiving optical system 41b. The light receiving optical system 41b includes a semi-transmissive mirror 43 disposed at 45 ° with respect to the incident optical axis, the reference pulse light 105 is also guided to the same optical axis as the reflected pulse light 106, and is condensed on the light receiving element 42, It is photoelectrically converted.
[0011]
The reception pulse signal S104, which is the output of the APD 42, is amplified by the signal amplification unit 5, and the amplified reception pulse signal S105 is supplied to the reception timing detection unit 6. The reception timing detection unit 6 includes a comparator unit 61 and a level conversion unit 62. The time measurement unit generates a reception timing signal S106 that is temporally stable even when the amplitude varies with respect to the input reception pulse signal S105. Output to 2. The detailed operation of the reception timing detection unit 6 will be described later.
[0012]
The time measurement unit 2 measures the time (pulse light travel time) from the pulse emission command S102 to the reception timing signal S106, and sends time data S112 to the calculation control unit 1. The arithmetic control unit 1 calculates the distance to the object to be measured based on the time data S112 and the speed of light.
[0013]
FIG. 2 is a diagram for explaining a distance measuring method by the apparatus of FIG. (1) and (2) in FIG. 2 show the relationship between the pulse emission command S102 and the reception timing signal S106 when the reference optical path 111 is selected. (3) and (4) show the relationship between the pulse emission command S102 and the reception timing signal S106 when the distance measuring optical path 110 is selected.
[0014]
Returning to FIG. 1, the actual ranging sequence will be described. The arithmetic control unit 1 confirms the level of the received signal from the distance measuring optical path 110 before the distance measurement (light quantity balancing process). First, the calculation control unit 1 minimizes the gain of the amplification unit 5 from the gain control signal S108, and the light transmittance adjustment filter 44 is transmitted through the drive unit 45 via the drive signal S109 and the transmittance is maximized in both the reference optical path 111 and the distance measuring optical path 110. Set to be. The light amount adjustment filter 44 is separated into a portion through which the light of the reference optical path 111 passes and a portion through which the light of the distance measuring optical path 110 passes for one filter. The light in the distance optical path 110 remains open and does not change. When the light in the distance measuring optical path 110 is attenuated, the light in the reference optical path 111 remains open and does not change.
[0015]
Next, the optical path switching unit 36 is opened on the reference optical path 111 side, and the arithmetic control unit 1 reads the reception level signal S107 obtained by peak-holding the output S105 of the amplification unit 5 by the level detection unit 7. At this time, the reception level S107 of the reference optical path 111 is adjusted in advance by the neutral density filter 35 so as to become a predetermined level. Next, the optical path switching unit 36 is opened on the distance measuring optical path 110 side, and the received signal level from the object to be measured is similarly measured by reading S107.
[0016]
When the received signal level from the object to be measured is higher than the signal level of the reference optical path 111, the light amount of the distance measuring optical path 110 of the light amount adjustment filter 44 is attenuated via the drive signal S109 and the drive unit 45, and 2 The signal levels of the two optical paths are adjusted to be equal. If the received signal level from the device under test is smaller than the signal level of the reference optical path 111, the gain of the amplifying unit 5 is increased via the gain control signal S108, and the received signal level from the device under test is used as a reference. It is set equal to the signal level of the optical path 111. In this case, since the signal level of the reference optical path 111 is increased by increasing the gain of the amplification unit 5, the light amount of the reference optical path 111 of the light amount adjustment filter 44 is attenuated via the drive signal S109 and the drive unit 45, It adjusts so that the signal level of two optical paths may become equal. The arithmetic control unit 1 enters the distance measuring operation after the signal levels of the two optical paths become equal.
[0017]
The optical path switching unit 36 opens the reference optical path 111 side and transmits the pulsed light 103 to the reference optical path 111. The reference pulse light 105 attenuated to a predetermined light quantity by the neutral density filter 35 is sent as the reception timing signal S106 to the time measurement unit 2 through the light receiving unit 4, the amplification unit 5, and the reception timing detection unit 6. As described above, the time measurement unit 2 measures the time S112 from the pulse emission command S102 to the reception timing signal S106, and the calculation control unit 1 measures the measurement distance in the reference optical path 111 based on the measurement time S112 and the speed of light. Find Lref.
[0018]
Next, the optical path switching unit 36 opens the distance measuring optical path 110 side and transmits the pulsed light 103 to the distance measuring optical path 110. The reflected pulsed light 106 reflected by the object to be measured returns to the distance measuring optical path 110, is detected by the light receiving unit 4, and the reception timing signal S106 is sent to the time measuring unit 2 as in the case of the reference optical path. The measurement distance Ls in the distance measuring optical path is obtained. The calculation control unit 1 subtracts the measurement distance Lref in the reference optical path from the measurement distance Ls in the distance measurement optical path, thereby canceling the error factor due to the fluctuation due to the temperature of the electric circuit, and the accurate distance to the object to be measured. L is calculated.
[0019]
FIG. 3 is a diagram showing details of the configuration of the distance measuring optical path 110, the reference optical path 111, the light transmitting unit 3, and the light receiving unit 4 in the distance measuring apparatus of the present embodiment shown in FIG. The pulsed light emitted from the semiconductor laser 32 is converted into a parallel light beam by the collimator lens 301 and is incident on the semi-transmissive prism 302 (corresponding to the optical path dividing unit 34). The transflective prism 302 has a characteristic of a ratio of transmission T: reflection R, for example, T: R = 1: 99, and the reference pulse light transmitted to the reference optical path 111 side is greatly attenuated.
[0020]
When the reference optical path 111 is selected by the optical path switching unit 36, the reference pulse light is reflected by the mirror 313, passes through the neutral density filter 35 and the light amount adjustment filter 44, and enters the semi-transmissive prism 311 (corresponding to the semi-transmissive mirror 43). Incident. The reference pulse light is reflected by the semi-transmissive prism 311 and then received by the APD 42 via the relay lens 312.
[0021]
On the other hand, when the distance measuring optical path 110 is selected by the optical path switching unit 36, the pulse light reflected by the semi-transmissive prism 302 and transmitted to the distance measuring optical path 110 side is transmitted from the collimator lens 304 to the mirror 305 and the objective lens 306. Then, it is transmitted as a distance measuring pulse light 104 toward the measurement object. The reflected pulsed light 106 reflected and returned from the measurement object is received by the objective lens 306 and enters the optical fiber 309 via the dichroic mirror 307.
[0022]
The dichroic mirror 307 has a characteristic of reflecting infrared light and transmitting visible light. The reflected pulsed light 106 incident on the optical fiber 309 is converted into parallel light by the collimator lens 310 disposed at the other end of the optical fiber 309, and then the light quantity adjustment filter 44 makes the light quantity equal to the reference pulsed light passing through the reference optical path. The light is attenuated, reflected by the mirror 317, and received by the APD 42 via the semi-transmissive prism 311 and the collimator lens 312.
[0023]
Here, the light amount adjustment filter 44 is a disk-like filter whose transmittance gradually changes with a predetermined gradient in the circumferential direction at the passage positions of the reference pulse light and the ranging pulse light, and the center thereof is a drive unit. (Drive motor) 45 is rotationally driven. Further, the reference pulse light passing position and the distance measuring pulse light passing position on the filter are on the circumferences of different radii, and the transmittance of the distance measuring light path is the position where the density gradient of the reference light path gradually changes. Is constant at the maximum, and conversely, the transmittance of the reference optical path is constant at the maximum at a position where the density gradient of the distance measuring optical path gradually changes.
[0024]
FIG. 3 further shows a collimating optical system for aligning the optical axes of the light transmitting and receiving optical systems in the direction of the measurement object. That is, for the operator 321, a collimating optical system is configured by the eyepiece lens 320, the reticle 319, the erecting prism 318, the focusing lens 308, and the objective lens 306. The dichroic mirror 307 has a characteristic of transmitting visible light. In the present embodiment, the collimation optical system, the light transmission optical system, and the light reception optical system are all configured on the same optical axis.
[0025]
Next, details of the reception timing detector 6 according to the present embodiment will be described with reference to the block diagram of FIG. 4 and the timing chart of FIG. FIG. 4 is a block diagram of the reception timing detection unit 6. FIG. 5 is a timing chart in the block diagram of FIG. The front-stage comparator unit 61 in FIG. 4 includes two delays (delay elements) 401 and 402 and three comparators 403, 404, and 405. The delays 401 and 402 use passive delay lines composed of coils, capacitors, and the like. Other delay elements such as an active delay line may be used.
[0026]
For higher accuracy, it is desirable that the pulse width of the input pulse signal is as narrow as possible. When the pulse width is 10 ns or less, it is desirable to use the ECL type comparator. This configuration example is based on the premise that an ECL type comparator is used. Therefore, a level conversion unit 62 for converting an output signal to a TTL level is connected.
[0027]
Next, the operation of the comparator unit 61 will be described. When the received pulse signal S105 is input to the comparator 403, the output S403 is output to the comparator 404 when the signal level exceeds a predetermined threshold, and the comparator 404 changes from the latch mode to the compare mode by this signal, At the same time, the output S404 changes from level H to level L. The latch mode is a mode for holding the output state, and the comparator mode is a mode for performing a comparing operation. In other words, when the output S403 becomes active (level H), the comparator 404 is enabled and performs a comparison operation.
[0028]
S401 of the two inputs of the comparator 404 is a signal obtained by delaying S105 by the delay 401 by about a half width of the pulse (pulse width at a value of about half of the amplitude). The two signals are large and small at the timing of the cross point. The relationship is reversed, and the output S404 changes from the level L to the level H at this timing.
[0029]
The comparator 405 changes from the latch mode to the compare mode at the rising edge of the output S404, and at the same time, the output S405 changes from the level L to the level H. Of the inputs of the comparator 405, S402 is a signal obtained by delaying S105 by the delay 402 set to a delay time approximately twice the delay time of the delay 401. The two inputs S401 and S402 are cross-point timings. The magnitude relationship is reversed, and the output S405 changes from level H to level L at this timing.
[0030]
Note that the output S403 changes from the level H to the level L when the reception pulse signal S105 becomes smaller than a predetermined threshold. However, the predetermined threshold may be set to a value sufficiently smaller than the level at which the cross point varies.
[0031]
As described above, as shown in FIG. 5, the output S405 of the comparator 405 is a signal whose logic is inverted by two cross points generated by pulse signals delayed by two delays having different delay times with respect to the original pulse signal S105. It becomes. That is, the front edge of the active pulse signal of output S405 is generated at the point (intersection) where the original pulse signal S105 and the level of output S401 intersect, and the output S405 is generated at the point (intersection) where the levels of output S401 and output S402 intersect. The trailing edge of the active pulse signal is generated. The active pulse signal of this output S405 becomes the reception timing signal S106.
[0032]
Here, the reason why the reception timing signal S106 is generated by the cross point in the present embodiment will be described. FIG. 6 is a diagram illustrating a change in reception timing when a reception pulse signal is detected at a certain threshold level. It can be seen that when the amplitude of the received pulse signal changes from the solid line amplitude level to the upper and lower broken line levels due to temperature and other environmental changes, the reception timing signal fluctuates back and forth by δt as shown in FIG. If this signal is used as it is as a reception timing signal, the reception timing varies and high-accuracy measurement cannot be achieved. Therefore, in the present embodiment, a pulse signal is generated by a cross point as a method for absorbing this variation.
[0033]
For example, consider the comparator 404 as an example. FIG. 7 is a diagram illustrating signal waveforms of the reception pulse signal S105 and the signal S401 obtained by delaying the reception pulse S105 by the delay 401 to be input to the comparator 404. As shown in FIG. 6, it can be seen that even if the amplitudes of the reception pulse signal S105 and the signal S401 fluctuate, the timing of the cross point does not fluctuate. Thereby, the timing which is not influenced by an environmental change is acquirable.
[0034]
If the rear edge of the reception timing can be generated by one cross point, high-accuracy measurement is possible if the rear edge is used as a reference for time measurement. However, in this embodiment, as described above, the ECL type is used for the comparator, and the level conversion unit 62 for converting the output signal to the TTL level (or CMOS level) is used. FIG. 8 is a circuit example for converting the ECL level to the TTL level. In this level conversion circuit, the input pulse is affected by the base capacitance of the transistor, and when the input pulse width changes, the delay time of the rear edge changes.
[0035]
For example, the case where the output S404 of the comparator 404 in FIG. 4 is used as the reception timing signal S106 via the level conversion circuit 62 as it is may be assumed. In such a case, since the rear edge of the output S404 is generated by the cross point, the rear edge is generated at a timing not affected by the fluctuation, but the front edge varies due to the influence of the amplitude of the pulse signal S105. That is, the output S404 is not affected by the timing of the rear edge, but the pulse width varies. If such a varying pulse width is input to the level converter 62, the timing of the rear edge of the final TTL output signal will change even if the cross point does not change with respect to the amplitude fluctuation.
[0036]
Therefore, in this embodiment, as described above, the timing is generated by cross points at both the front edge and the rear edge of the reception timing signal so as not to be affected by the pulse width. Thereby, even when the level conversion circuit as shown in FIG. 8 is used, the reception timing signal S106 which is stable in terms of timing can be output.
[0037]
As described above, even when the amplitude of the reception signal varies, the reception timing signal S106 that is stable in terms of timing can be generated, and as a result, distance measurement with high accuracy is possible. Further, compared to the case where a differentiation circuit is used, it is less affected by variations in circuit constants, making it easy to select components and making the manufacturing process easier. As a result, parts costs and manufacturing costs are also reduced.
[0038]
In the above embodiment, the example of the distance measuring device in the surveying instrument has been described, but it is not necessary to limit to this content. When generating a pulse signal corresponding to an input signal, the present invention can be applied to any application that needs to generate a pulse signal at a timing that is not affected by fluctuations in the amplitude of the input signal. Further, the distance measuring device need not be limited to those mounted on the surveying instrument. For example, it can be used for an apparatus that measures the distance between vehicles. That is, the present invention can be applied to any application that needs to measure the distance to a target.
[0039]
In the above-described embodiment, the signal S105 is delayed by the delay 401 by approximately the half width of the pulse (pulse width at about half the amplitude), and the signal S105 is delayed by the delay 402 by twice the half width of the pulse. Although described, it is not necessary to limit to this content. The value may be varied within a range in which the cross point can be detected with a value within the pulse width of the signal S105.
[0040]
In the above embodiment, the example in which the signal S105 is input to the delay 401 and the delay 402 and the delay value of the delay 402 is set to about twice that of the delay 401 has been described. Absent. The delay 401 and the delay 402 having the same delay value may be used, and the output of the delay 401 may be input to the delay 402.
[0041]
In the above embodiment, an example in which an ECL element is used for the comparators 403 to 405 has been described. However, the present invention is not limited to this. It may be an element of another technology such as TTL or CMOS. The present invention can be applied even when the level conversion circuit is not used.
[0042]
In the above embodiment, an example of pulsed laser light has been described, but it is not necessary to limit to this content. Any light can be used as long as it can irradiate the target with the aim and can be received by the light receiving element when the light is reflected from the target.
[0043]
In the above embodiment, the case where the signal is at a high level with respect to the GND has been described by the so-called positive logic, but it is not necessary to limit to this content. The present invention can also be applied to a case where a circuit or the like is configured with a so-called negative logic in which the GND level is active with respect to a certain signal level. That is, in this specification, the invention is expressed using positive logic for convenience of explanation, but the present invention includes what is constituted by both positive logic and negative logic.
[0044]
In the above-described embodiment, the example in which the comparator is used to compare the levels of the two inputs has been described. However, the present invention is not limited to this. That is, any circuit or element that can compare two input levels and output a signal corresponding to the comparison result may be used. In this specification, these are referred to as comparator means.
[0045]
In this specification, light transmission means sending out, irradiating, and emitting light.
[0046]
Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.
[0047]
【The invention's effect】
Since the present invention is configured as described above, for example, even if the amplitude of the input signal varies, it is possible to generate a pulse signal corresponding to the input signal at a stable timing. In addition, when such a pulse signal generation circuit is used in a distance measuring device, it is possible to perform distance measurement with high accuracy at low cost.
[Brief description of the drawings]
FIG. 1 is a block diagram of a distance measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a distance measuring method by the apparatus of FIG. 1;
FIG. 3 is a diagram illustrating details of a configuration of a distance measuring optical path, a reference optical path, a light transmitting unit, and a light receiving unit.
FIG. 4 is a block diagram of a reception timing detection unit.
FIG. 5 is a timing chart in the block diagram of FIG. 4;
FIG. 6 is a diagram illustrating a change in reception timing when a reception pulse signal is detected at a certain threshold level.
FIG. 7 is a diagram illustrating signal waveforms of a reception pulse signal S105 and a signal S401 delayed by a delay.
FIG. 8 is a circuit example for converting an ECL level to a TTL level.
[Explanation of symbols]
1 Operation control unit
2 hour measuring part
3 Light transmitter
4 Light receiver
5 Signal amplifier
6 Reception timing detector
61 Comparator section
62 Level converter
401, 402 delay
403-405 Comparator

Claims (6)

A pulse signal generation circuit for generating a pulse signal corresponding to an input signal,
First delay means for delaying the input signal for a first time which is a value within the signal width of the input signal and outputting a first delayed signal;
Second delay means for delaying the input signal by a second time longer than the first time and having a value within twice the signal width of the input signal and outputting a second delayed signal;
Based on the input signal, the first delay signal, and the second delay signal, an intersection of output levels of the input signal and the first delay signal is detected to generate a front edge of the pulse signal. And an intersection detection means for detecting an intersection of output levels of the first delay signal and the second delay signal to generate a rear edge of the pulse signal to generate the pulse signal. A pulse signal generation circuit. The pulse signal generation circuit according to claim 1,
The intersection detection means includes:
First comparator means for outputting the first signal as active when it is detected that the input signal is above a predetermined level;
Enabled when the first signal becomes active, and outputs a second signal as active when enabled and when the level of the input signal is lower than the level of the first delay signal. Two comparator means;
The signal is enabled when the second signal becomes active, and the third signal is activated when enabled and when the level of the first delay signal is higher than the level of the second delay signal. And third comparator means for inverting and outputting the third signal when the level of the first delay signal is lower than the level of the second delay signal,
The pulse signal generation circuit characterized in that the third signal output from the third comparator means is the pulse signal. The pulse signal generation circuit according to claim 1 or 2,
The first time corresponds to a pulse width at about half of the amplitude of the input signal, and the second time corresponds to about twice the pulse width at about half of the amplitude of the input signal. A pulse signal generation circuit characterized by the above. The pulse signal generation circuit according to any one of claims 1 to 3,
The intersection detection means uses an ECL element,
A pulse signal generation circuit further comprising conversion means for converting the pulse signal output from the ECL element from an ECL level to a TTL level. A light sending means for sending light for distance measurement toward a target based on a distance measurement command signal;
A light receiving means for receiving the distance measurement light reflected by the target and outputting a light reception signal;
A time measurement end signal generating means for generating a time measurement end signal based on the received light signal;
Time measurement means for starting time measurement based on the distance measurement command signal, ending time measurement based on the time measurement end signal, and measuring a light travel time from the light transmission to the light reception;
A distance measuring device comprising: an optical traveling time measured by the time measuring means; and a computing means for computing a distance to the target based on the obtained optical traveling time,
The time measurement end signal generation means includes the pulse signal generation circuit according to any one of claims 1 to 4,
An input signal of the pulse signal generation circuit corresponds to the light reception signal, and a pulse signal of the pulse signal generation circuit corresponds to the time measurement end signal. A surveying instrument comprising the distance measuring device according to claim 5.

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