JPH0346588A - Laser receiver - Google Patents

Abstract

PURPOSE:To make the photoelectric conversion sensitivity constant even if a sensitivity characteristic of an APD is varied by allowing a reference light to be made incident and monitoring directly photosensitivity of the APD, setting an operating voltage, and also, correcting a level variation of the reference light caused by a temperature. CONSTITUTION:When a control bias signal 5 is inputted before several masec of an emission of a laser light, a changeover switch 6 is closed and a high voltage 4 for a photodetector increases gradually an APD applied voltage of a photodetector 1. On the other hand, by the signal 5, a gate circuit 14 allows a reference signal and a clock signal to pass through they are applied to a reference light source 9 through a driving circuit 11, and its output goes into the detector 1 and outputted through an amplifier 2. In this case, when the output of the light source 9 is compensated 12 so as to become constant against a temperature, even if sensitivity of an APD is varied due to a temperature variation, a voltage applied to the APD rises until an output level of the amplifier 2 reaches a threshold of a comparator 8, and according ly, photoelectric conversion sensitivity rises. Subsequently, when it reaches a threshold, the optical comparator 8 operates,and by its signal, a switch 6 is opened, the voltage rise of the detector 1 stops, and simultaneously, the light source 9 stops its operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser receiver used in a distance measuring device (4) using pulsed laser light and converting laser reflected light from a target into an electrical signal. It is something.

[Conventional technology]

Figure 4 is a configuration diagram showing this type of conventional device. (1) in Figure 9
is a photodetector that photoelectrically converts the received laser light, (2)
is an amplifier that amplifies the signal from the photodetector (1).

(3) is a stop signal for counting distance in the distance measuring device, (4) is a high voltage for the photodetector, and C5 is a bias control signal that controls the period of applying high voltage to the photodetector.

(61 is a changeover switch that is opened and closed by the bias control signal (5), (7) is a high voltage distribution circuit that distributes the high voltage 14+ for the photodetector to create a predetermined operating voltage, and (8) is an amplifier (
2) is a comparator that converts the output signal into a binary value; (9) is a counter circuit that counts the binary output of the comparator (8) and operates the high voltage distribution circuit +71i.

- In the membrane, an avalanche photodiode (hereinafter referred to as APD) is used as a charge conversion element of the photodetector (1).

Since the photoelectric conversion sensitivity of the APD changes depending on the temperature during operation, the photoelectric conversion sensitivity is kept constant by varying the operating voltage applied to the APD in accordance with the ambient temperature.

A method of compensating for the APDO photoelectric conversion sensitivity applied to the above conventional device will be described below. A few m5ec before the pulsed laser beam is emitted from the range finder, apply the bias control signal (5) and close the changeover switch (6).

Apply photodetector high voltage (4) to the APD. In the process of increasing the voltage applied to the APD from 0 with a predetermined time constant, a breakdown phenomenon occurs and the noise current increases rapidly.

The noise current is converted into voltage, passed through an amplifier (2), and divided into two voltages by a comparator (8). The number of this binary noise is counted, and when it reaches a predetermined count value, the selector switch +61'i is opened and at the same time the high voltage distribution circuit (7
) and lower the voltage by a certain ratio.

By the above operation, the operating voltage of the APD can always be set to a value lower than the breakdown voltage by a certain amount before laser emission.

In a general APD, the temperature change rate of the operating voltage that is changed to keep the photoelectric conversion sensitivity constant is about 2.2 V/''C, and the temperature change rate of the breakdown voltage is about 2.4 V/''C.

Therefore, by detecting the breakdown voltage and setting the operating voltage, the APDO photoelectric conversion sensitivity can be kept constant against temperature changes.

[Problem to be solved by the invention]

In the conventional device described above, since the operating voltage of the APD is determined by lowering the breakdown voltage by a certain ratio, the APD
The photoelectric conversion sensitivity does not become constant when the value changes to something else. That is, since the photoelectric conversion sensitivity differs between devices, there is a problem in that the APD to be used must be selected so that there is no large sensitivity change.

This invention is a means to solve this problem.

Directly monitor APDO photosensitivity using a reference light source,
The purpose is to obtain a laser receiver that does not require APD selection by determining the operating voltage of the APD.

[Means to solve the problem]

A laser receiver according to the present invention generates a reference light,
A means for inputting the signal to the APD, and a means for detecting the signal level (7) and setting the operating voltage of the APD.

The present invention is equipped with a reference light level correction means that can correct the level of the reference light even if the level of the reference light changes with temperature.

[Effect]

According to this invention, 9. Even if the sensitivity characteristics of the APD change, a constant photoelectric conversion sensitivity can always be obtained.

〔Example〕

FIG. 1 is a block diagram showing a first embodiment of this invention, FIG. 2 is a second embodiment of this invention, and FIG. 3 is a block diagram showing a third embodiment of this invention. )~f61. (8
1 is the same as the conventional device.

In the figure, (9) is a reference light source that can be realized with a light emitting diode or semiconductor laser, etc. and generates light containing the same wavelength component as the pulsed laser light of the range finder, and αO is the pulsed laser light from the emission component of the reference light source f91. αD is an interference filter that transmits only the same wavelength components, αD is a drive circuit that pulse-modulates the output light of the reference light source, and ti is a drive circuit that detects temperature to compensate for changes in luminous efficiency of the reference light source due to temperature. α4, a temperature compensation circuit that generates a signal that changes the driving conditions of the wholesaler
is the reference light source's (8) reference clock generator that generates a reference clock signal that pulse-modulates the output light, and Cl3 is the bias control a signal (5)
and supplies the reference clock signal to the drive circuit aυ.

A gate circuit that stops the operation of the drive circuit αD by the signal of the comparator (8), and the α field is a half mirror 9a that can reflect and transmit the output light of the reference light source (9) [9 is realized by a silicon photodiode, etc. that does not change in temperature. huff mirror a
! 9 is a reference photodetector that detects the reflected tip metal and converts it into an electrical signal; Qn is a filter that attenuates the output light of the reference light source;
aS is an optical fiber that guides the transmitted light of the optical filter aD to the photodetector (1), (19 is a level detection circuit that averages the signal from the reference optical output detector ae, and CXJ is a binary threshold level that is set externally. This is a variable comparator that has the function of being able to vary to a predetermined value using a signal.

Operations common to FIGS. 1 to 3 will be explained using FIG. 1 above. When the side bias signal (5) is input several meters before the laser beam is emitted, the changeover switch (6)
is closed, the photodetector high voltage +41 is applied to the photodetector (1), and the voltage applied to the APD gradually increases. - The force control bias signal (51 causes the gate circuit α4 to pass a reference clock signal having a period within the passband of the amplifier (2) and is applied to the reference light source (9) through the drive circuit. ) is pulse-modulated, and the output of the photodetector (1)
The signal enters the circuit and is output as a pulse signal via an amplifier (2). At this time, the output of the reference light source (9) is adjusted to the temperature compensation circuit α
3 to keep it constant against temperature changes, even if the photoelectric conversion sensitivity of the serial APD changes due to temperature changes, the output level of the amplifier (2) will be the same as that of the comparator (8).
1 reaches the binarization threshold level of 1, the voltage applied to the APD increases. That is, photoelectric conversion sensitivity increases.

When the binarization threshold of the comparator (8) is reached, the comparator (81) is activated, and the changeover switch +61 is not opened due to its signal, and the voltage increase of the photodetector (1) is stopped. At the same time, the operation of the reference light source (9) is stopped. Through the above operation, the applied voltage of the APD maintains a constant photoelectric conversion sensitivity regardless of temperature changes and regardless of variations in the characteristics of each APD. In the case of this invention, strictly speaking, the receiving sensitivity of the entire receiving system including the amplifier (2) is determined.
When viewed as a distance measuring device, there is no problem as long as the sensitivity is constant throughout the receiving system.

The second reason is that a part of the output of the reference light source (9) is converted into a half mirror without using the temperature compensation circuit 03 including a temperature sensor as a reference light level correction means for correcting temperature changes in the output of the reference light source (9). α9 is detected by the reference light output detector 00, and its average value is detected by the level detection circuit α9.

The driving conditions of the driving circuit Qll are changed so that the output of the reference light is constant. In this method, if the output of the reference light is too small, another amplifier or the like is required, so the output of the reference light source +91 is driven to be large.

The output level of the reference light is lowered by using an optical filter 0'n and a fiber tube in the optical path for inputting the reference light to the photodetector fil. The fiber 〇 mallet is the reference light source (
9), interference filter 0[1,) - humirar (LS.

The part consisting of the reference photodetector ae and the filter an is the photodetector (11), which is effective when the VC!!I [pupil cannot be detected] near the photodetector (11).

Figure 3 shows that the output of the level detection circuit 0 shown in Figure 2 is not inputted to the drive circuit 0υ, but is inputted to a variable comparator ■ that has a circuit that can vary the binarization threshold level. This is to compensate for fluctuations in the output level of the reference light source (9).

Although not shown in the figure, the photodetector (1) is generally placed at the focal position of the receiving optical system that collects the laser reflected light from the target.
The receiving optical system includes an interference filter that transmits only the wavelength component of the pulsed laser light to be used.

Therefore, it goes without saying that the interference filter a1 used in the first to third colors may be the interference filter in the receiving optical system.

〔Effect of the invention〕

As explained above, in this invention, since the operating voltage of the APD is always changed so as to keep the receiving sensitivity of the laser receiver constant, it is no longer dependent on variations in the characteristics of the APD.
This has the effect of eliminating the need for PD selection (12).

Furthermore, since the sensitivity is verified every time immediately before laser emission, it has the effect of making it possible to monitor abnormalities online.

[Brief explanation of drawings]

FIGS. 1 to 3 show the first example of this invention. Figures illustrating the second and third embodiments, and FIG. 4 are configuration diagrams illustrating a conventional laser receiver. In the figure, fil is a photodetector, (2) is an amplifier, and (3)
is a stop signal, C4) is a high voltage for the photodetector, (5) is a bias control signal, C6) is a changeover switch, and (7) is a high voltage distributor. (8) is a comparator, C9) is a reference light source, fil is an interference filter, Qll is a drive circuit, αa is a temperature compensation circuit, (I3 is a reference clock generator, a◆ is a gate [gJ
aS is a half mirror, 9αQ is a reference light output detector,
a7) is an optical filter. αa is an optical fiber, aS is a level detection circuit, and (A) is a variable comparator. Note that the same reference numerals in the two figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A photodetector that receives laser reflected light from the target;
A laser beam is emitted to apply a high voltage to an amplifier that amplifies the output of the photodetector, a comparator that binarizes the output signal of the amplifier, and an APD (avalanche photodiode) in the photodetector. a changeover switch that is energized by a bias control signal output for a predetermined period of time and cut off by an output signal of the comparator; a reference light source that generates a reference light of a predetermined intensity to the photodetector; a reference clock generation circuit that generates a reference clock signal that pulse-modulates the reference light; a reference clock generation circuit that applies the reference clock signal to the drive circuit according to the bias control signal; a gate circuit that controls the operation of the drive circuit to stop it; an interference filter that transmits only light having the same wavelength component as the laser beam to be used from the output light of the reference light source; and an interference filter that detects the temperature and controls the output of the reference light source. A laser receiver equipped with a temperature compensation circuit that corrects the temperature so that it remains constant against temperature changes. (2) a photodetector that receives laser reflected light from the target;
A laser beam is emitted to apply a high voltage to an amplifier that amplifies the output of the photodetector, a comparator that binarizes the output signal of the amplifier, and an APD (avalanche photodiode) in the photodetector. a changeover switch that is energized by a bias control signal output for a predetermined period of time and cut off by an output signal of the comparator; a reference light source that generates a reference light of a predetermined intensity to the photodetector; a reference clock generation circuit that generates a reference clock signal that pulse-modulates the reference light; a reference clock generation circuit that applies the reference clock signal to the drive circuit according to the bias control signal; a gate circuit that controls the operation of the drive circuit so as to stop it; an interference filter that transmits only light having the same wavelength component as the laser beam to be used from the output light of the reference light source; and a part of the output light of the reference light source. It comprises a half mirror for reflecting, a reference light output detector for detecting the reflected light of the half mirror, and a level detection circuit for averaging the output of the reference light output detector, and the output signal of the level detection circuit is A laser receiver characterized in that driving conditions of the reference light source are changed so as to be constant, and an optical fiber and an optical filter are provided between the half mirror and the photodetector. (3) a photodetector that receives laser reflected light from the target;
an amplifier that amplifies the output of the photodetector; a variable comparator that binarizes the output signal of the amplifier and can vary the binarization threshold level; and an APD in the photodetector.
The high voltage applied to the avalanche photodiode is energized by a bias control signal output for a predetermined period before the laser beam is emitted, and is cut off by the output signal of the comparator. a reference light source that generates reference light to the photodetector; a drive circuit that drives the reference light source; a reference clock generation circuit that generates a reference clock signal that pulse-modulates the reference light; A gate circuit that controls the operation of the drive circuit by applying a control signal to the drive circuit and stopping it by the output signal of the comparator; an interference filter that transmits only light; a half mirror that reflects a portion of the output light of the reference light source; a reference light output detector that detects the reflected light of the half mirror; A level detection circuit that averages and varies a binarization threshold level of the variable comparator using the output signal thereof, and an optical fiber and an optical filter provided between the half mirror and the photodetector. A laser receiver characterized by: