JPH01102381A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To measure a distance in the max. capacity state, by a method wherein the rate of the voltage to be dropped is changed corresponding to the circumferential temp. to continue voltage drop to calculate the optimum bias voltage and performing APD (Avalanche Photo Diode) bias setting conforming to the circumferential temp. CONSTITUTION:The rising of APD bias voltage is stopped at a breakdown voltage level on the basis of micronoise generated by an APD 15 itself by a current limiting resistor 9, a charging condenser 20, an FET 12, a diode 14, the APD 15, an amplifier 16 and a breakdown detection circuit 17. Then, on the basis of time data generating a breakdown phenomenon, the charging condenser 20 is discharged corresponding to the circumferential temp. by an FET 13, a pulse generator 18 and an positive temp. characteristic thermistor 19 and APD bias voltage is dropped to set the optimum bias voltage. Therefore, the APD 15 can be always operated in an ideal state corresponding to the circumferential temp. and, therefore, distance measuring capacity can be prevented from receiving the adverse effect of the circumferential temp. and a distance can be measured in the max. capacity state.

Description

[Detailed description of the invention] [Industrial application field] This invention is a distance measuring device that uses laser beams.

In particular, the receiving APD (Avalanche Pho
This invention relates to an improvement in the bias application method (to diodes).

[Conventional technology]

Fig. 5 is a configuration diagram showing a conventional distance measuring device equipped with a photodetector. In Fig. 9, (1) is a laser oscillator, (2) is a transmitting optical system, (3) is a receiving optical system, and (4) For example, PD(P
(5) Photodetector using photodiode etc.
(6) is a high-voltage circuit, (
7) is a counting circuit, and (8) is a power supply.

In this distance measuring device, a pulsed laser beam emitted from a laser oscillator (1) is beam spread-adjusted by a transmitting optical system (2) and irradiated toward a target, while at the same time a part of the laser beam is illuminated. The signal is input to the detector (4) and converted into a pulsed electrical signal (hereinafter this signal will be referred to as a start pulse signal) indicating the timing at which the laser beam was emitted.

The laser beam reflected from the target is focused by the receiving optical system (3), and the photodetector (5) generates a pulsed electrical signal (
This signal is hereinafter referred to as a stop pulse signal). High voltage circuit (61ti A of the above photodetector (5)
The power supply (8) is used to apply a high voltage to the PD to create an appropriate bias state and to supply a high voltage current for laser beam generation to the laser oscillator (1), and the power supply (8) is connected to the high voltage circuit described above. (6), photodetector (4), photodetector (5)
, which supplies electrical energy to electronic circuits such as the counting circuit (7).

In this way, the distance is measured using the radar oscillator (1), transmitting optical system (2), receiving optical system (3), photodetector (4), photodetector (5), high voltage circuit (6), and power source (8). A start Hals signal and a stop pulse signal indicating the time at which the laser beam was emitted are generated, and a counting circuit (7) calculates equation (1) using these start pulse signal and stop pulse signal. By doing this, the distance Ri to the target can be determined.

T R-Seal・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・－・・・・・・・・・・・・・・・
...... (11R: Distance to target (c) C: Speed of light (3X 10"rry'5ec) T Time interval between start pulse signal and stop pulse signal (Se
c) Furthermore, since the laser beam reflected from the target is weak, the photodetector (5) that generates a stop-noise signal in response to this is generally used in APD's that have a light multiplication function. However, it is devised to maximize the APD function by applying a bias voltage to the APD just before the breakdown phenomenon occurs.Figure 6 shows the circuit configuration of this photodetector (5). In the figure, (9) is the current limiting resistor, (11° circle is the first
．． Second capacitor, Q21. aa each 1st. Second
Field FET Trans
ister).

α4 is a diode, +151 is an APD, αG is an amplifier, αη is a breakdown detection circuit, and the current limiting resistor (9) and the breakdown detection circuit aη are connected to the high voltage circuit (6) and the counting circuit (7), respectively. has been done.

In this detection unit (5), the APD plays the role of converting the laser beam reflected from the target into a pulsed electrical signal, and the amplifier uea amplifies this pulsed electrical signal to generate a stop pulse signal. At the same time, the above APD(I
It serves to amplify the micronoise generated when s causes a breakdown phenomenon to an appropriate value. The breakdown detection circuit α is a circuit (7) that counts only the stop pulse signal among the micro noise and stop pulse signals mentioned above.
The APD (15
1t" generates a timing signal for bias control. This timing signal causes the first and second F E
T C12+, (13 is normally turned on, turned off just before laser emission, and turned on again when the APDα9 causes a breakdown phenomenon, and when turned on, each of the current side root The resistor (9) and the second capacitor αυ are electrically grounded.

Here, the above 1. The capacitance value of the second capacitor Q[,
- Since the high voltage of the high voltage circuit (6) is applied through the above-mentioned 1.
Second capacitor α0. The first battery is charged at a ratio of (K-1):1 and a bias voltage is applied to the APD (Is). second capacitor αQ;

As charging to αυ progresses and the bias voltage increases, A
When the sensitivity of PDQ51 increases and reaches a voltage slightly higher than the bias voltage that exhibits the highest sensitivity (hereinafter this bias voltage is referred to as the maximum bias voltage), APD15
) causes a breakdown phenomenon and generates micronoise. Then, this micronoise is detected by the breakdown detection circuit α.

Since the current limiting resistor (9) and the second capacitor αυ are grounded by the timing signal that is the output of this circuit, the voltage applied to the APD (15) drops by twice l/'; If the value of the constant is selected so that the voltage ratio is the ratio of the difference between the bias voltage that causes the breakdown phenomenon (hereinafter referred to as the gold breakdown voltage) and the optimal bias voltage, the bias of APDQ9 can be adjusted. The voltage will be set to approximately the optimum value.

Note that the diode circle serves to prevent current from flowing out from the first capacitor +1 (l) and lowering the APD bias voltage when the current limiting resistor (9) is grounded. The breakdown voltage is detected using the micro-noise generated by the photodetector +51HAPD itself, and the bias voltage is set to a value approximately equal to the optimum bias voltage by lowering the bias voltage at a fixed ratio from this value. Because I do.

APDQ51 can operate in a nearly optimal sensitivity state.

[Problem that the invention seeks to solve]

In the above photodetector, the optimal bias voltage is set by lowering the APD bias voltage from the breakdown voltage at a constant ratio, but the breakdown voltage vs. the breakdown voltage - optimal bias voltage The ratio of the voltage difference between This has the disadvantage that it may not be carried out in a sufficiently compatible state, and as a result, the sensitivity of the APD cannot be fully utilized.

This invention solves the above problems by changing the ratio of the voltage that lowers the APD bias voltage from the breakdown voltage depending on the ambient temperature. The purpose is to prevent the ranging ability from being influenced by temperature by making it possible to fully draw out the range.

[Means for solving problems]

The conventional photodetector includes a positive temperature characteristic thermistor that discharges the current of the capacitor while changing the discharge time constant according to the ambient temperature by utilizing the temperature change characteristics of the resistor, and a positive temperature characteristic thermistor that discharges the current of the capacitor while changing the discharge time constant according to the ambient temperature, and the operation time of the discharge to an appropriate value. Add a pulse generator that generates a pulse with a constant pulse width to set the pulse signal with a constant width output from the pulse generator, and set the discharge time constant according to the ambient temperature using a positive temperature characteristic thermistor and FET. By changing the voltage and discharging the capacitor, the ratio of the voltage dropped from the breakdown voltage of the APD bias voltage can be changed depending on the ambient temperature.

[For production]

In this invention, the ratio of the voltage that lowers the human PD bias voltage from the breakdown voltage is made to change depending on the ambient temperature using a positive temperature characteristic thermistor, pulse generator, FIT, etc., so that the APD is independent of the ambient temperature. The sensor always performs optimally, and its ranging ability is unaffected by temperature.

〔Example〕

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and 1
9), a2. (13 to α are the same as before, α
The mark is a pulse generator, αI is a positive temperature characteristic thermistor, and ■ is a charging capacitor, which plays the same role as the first capacitor αl. In addition, FIG. 2 shows the pulse generator 0
This is a diagram showing the configuration of the second circuit. In Figure 1, (2) is a time constant capacitor, (2) is a time constant resistor, and is a Hawanshot multivibrator. The input and output terminals are the breakdown detection circuit ( 7), is connected to the second FBT (13).In such a configuration, the current limiting resistor (9) is connected to the second FBT (13).
), charging capacitor ■, FET (13, diode α
4) The APD (151), amplifier αe, and breakdown detection circuit αη operate in the same way as a conventional photodetector.

Bias voltage starts to be applied to APDQ5) immediately before laser distance measurement, and as the bias voltage increases, the APD (Is
) causes a breakdown phenomenon, the timing signal of the breakdown detection circuit αη and the slope of the FBTo2° diode α stop charging the charging capacitor (2) to prevent the APD bias voltage from exceeding the breakdown voltage. It has been found through experiments that there is a correlation between the optimum voltage drop ratio and temperature, and the lower the temperature, the larger the optimum voltage drop ratio becomes. FIG. 3 shows this situation, and has a characteristic that has a negative slope downward to the right with respect to temperature T. Therefore, by controlling the bias so that the ratio of the voltage drop matches the characteristic shown in FIG. 3 and dropping the voltage from the breakdown voltage, it is possible to perform the optimum bias setting suitable for the ambient temperature. The second FgTα sensor, pulse generator and positive temperature characteristic thermistor (19) are electronic circuits for voltage drop for this purpose, and the pulse generator α mark of these is as shown in Figure 2. Constant capacitor C2υ
It consists of a time constant setting component (2) of a time constant resistor (support) and a one-shot multivibrator (2) that generates a pulse of a constant width according to the time constant of these time constant components. Low-+Hi in circuit α
APD using the timing signal to switch to gh as a trigger
When (15) causes a breakdown phenomenon, (2)
A pulse signal W having a constant width as shown in the equation is generated.

WThA-C,R,・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...(2) A: Proportionality constant C1: Capacitance value of time constant capacitor R,: #
The resistance value of the resistor and the second FgTC13 and positive temperature characteristic thermistor α9
The charging capacitor (2) is discharged by the switch function and discharge function of 13T respectively while the pulse signal is at the logic level High, that is, for a certain time width W. At this time, the positive temperature characteristic thermistor 11 is activated as the temperature becomes lower. Since the resistance value has the characteristic of decreasing, this and the resistance value of the charging capacitor circle.

The discharge time constant determined from the capacitance value also decreases as the temperature decreases, as shown in equation (3).

τIC2・u, (T)・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
......(3) C8: Capacitance value of charging capacitor T: Ambient temperature R1 (7): Resistance value of positive temperature characteristic thermistor (T, <T
, then R* (Tt) < R* (TJ) Therefore, the rate at which the charging capacitor ■ drops from the breakdown voltage due to discharge during the fixed time width W of the pulse signal is 2.
varies depending on the ambient temperature and is expressed as in equation 4).

Zxl-erT = t-eA IICtRt aCz
Rzer) , , , , , 1. , -(41) Therefore, select the capacitance and resistance values of the time constant capacitor 1 and the time constant resistor @ of the positive temperature characteristic thermistor α so that the voltage drop ratio 2 matches the characteristics shown in Figure 3. ba, APD
Since the ratio of the voltage at which the bias voltage is lowered from the breakdown voltage can be made approximately equal to the optimum voltage drop ratio, the APD bias voltage can be set in an approximately ideal state depending on the ambient temperature.

Figure 4 shows this situation, and shows the terminal voltage of the charging capacitor (2), the output of the amplifier (α), and the output of the pulse generator (a) on the time axis (,), (b), and (), respectively. C
) as shown in the figure.

In the figure, t indicates the time when APD (Is) causes a breakdown phenomenon and generates micronoise.

(,)T in the figure! The curves T, T=T, respectively, show voltage drop characteristics due to discharge when the ambient temperature is Tl@Tz (Tx<Tt).

From these figures, the rise in APD bias voltage stops at the same time as APDQ51 generates micronoise, and the discharge time constant is controlled according to the ambient temperature by the resistance temperature change characteristic of the positive temperature coefficient thermistor α port.
It can be seen that the voltage drop of the APD bias voltage from the breakdown voltage is also set in accordance with the ambient temperature.

In the end, the photodetection section configured in this way requires a current limiting resistor (9), a charging capacitor circle, a 10th FITα2. Diode α41. APD (151, APD bias voltage rise due to amplifier αe and breakdown detection circuit α) eAPDQs stops at the breakdown voltage level based on the micro-noise generated by itself, and at the same time, based on the time information when the breakdown phenomenon occurred. 2 F
BTQ3. Pulse generator and positive temperature characteristic thermistor α
Accordingly, the charging capacitor (2) is discharged according to the ambient temperature, and the APD bias voltage is lowered to set the optimum bias voltage. Therefore, the APD (15) can always be operated in an ideal state according to the ambient temperature, and therefore, it is possible to prevent the ranging ability from being affected by the ambient temperature.

〔Effect of the invention〕

As explained above, in this invention, the conventional photodetector detects the breakdown voltage of the APD using micronoise generated by the APD itself, and sets the bias of the APD by dropping the voltage at a fixed ratio from this breakdown voltage. Instead of 1) changing the ratio of the voltage drop depending on the ambient temperature to lower the voltage to find the optimum bias voltage, 9) APD bias settings can be made in accordance with the ambient temperature. Therefore, the light detection ability of the APD can be brought out at its best at all times, and therefore, distance measurement can always be performed at its best performance without being affected by the ambient temperature.

Here, a case where a one-shot multivibrator is used is shown as an example of the configuration of the pulse generator, but the method is not limited to this, and methods using play lines and gates, gate ICs, and delay resistors are also possible.

A number of methods are possible, including the use of capacitors.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a pulse generator, FIG. 3 is a diagram showing the relationship between the optimum voltage drop ratio and temperature, and FIG. ), (b),
(c) ij, respectively, the terminal voltage of the charging capacitor ■, the output of the amplifier a, the output of the pulse generator (181). Figure 5 is a diagram showing the configuration of the distance measuring device. Figure 6 is a diagram showing the configuration of a conventional photodetector. In the figure, +II is a laser oscillator, (2) is a transmission optical system, and (3
) is the receiving optical system, (4) is the photodetector, (5) is the photodetector, (6) is the high voltage circuit, (7) is the counting circuit, (8) is the power supply, and (9) is the current limiting resistor. , α[, αυ is the first . second capacitor, a2. αken is the first. 217) PET,
Q41H (, t-e QShAPn, (lG is the amplifier, 0η is the breakdown detection circuit, ttS is the pulse generator, dark is the positive temperature characteristic thermistor, ■ is the charging capacitor, @ is the time constant capacitor, (support) ) is a time constant resistor, and (2) is a one-shot multivibrator. In Figure 1, the same or equivalent parts are indicated with the same symbol superimposed.

Claims (1)

[Claims] A high voltage circuit that generates a high voltage, a current limiting resistor that limits the current flowing from the high voltage circuit, a capacitor that accumulates the current flowing through the resistor and gradually increases the voltage, and a high voltage connected to the capacitor. or the first FET (Field Effect Tr
ansister), a diode that prevents current from flowing out of the capacitor when the high voltage is cut off, and a diode that changes the discharge time constant using the characteristic that the resistance value changes depending on the surrounding temperature, and the capacitor. A positive temperature coefficient thermistor that serves to discharge and lower the voltage of the capacitor, a second FET that serves to sustain or interrupt the discharge operation, and light multiplication using the high voltage stored in the capacitor as a bias source. APD (Avalanche)
e PhotoDiode) and A, which exhibits the highest sensitivity.
The APD bias voltage is slightly higher than the PD bias voltage.
an amplifier that performs amplification to capture the micronoise that occurs during the breakdown phenomenon that occurs when
A breakdown detection circuit detects as timing information the bias voltage that causes the APD to break down due to the micronoise, and generates a pulse signal with a constant pulse width based on the timing information, and uses this pulse signal to control the second FET. It consists of a pulse generator that serves to lower the voltage of the capacitor by controlling the
The timing signal from the breakdown detection circuit and the first FET cause the APD to cause a breakdown phenomenon, and at the same time stop the increase in the APD bias voltage, and the timing signal, the pulse signal of the pulse generator, and the positive temperature characteristic thermistor. By changing the discharge time according to the ambient temperature and causing the discharge, the APD bias voltage is lowered according to the ambient temperature,
A distance measuring device characterized by comprising a photodetecting section that allows a PD to operate optimally.