JP2002333476A - Light-emitting circuit for instrument for measuring distance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely emit a light pulse of a short pulse width to provide desired distance measurement precision, in a distance measuring instrument for measuring a distance up to an object using the light pulse from a semiconductor laser. SOLUTION: An input voltage (Vb) of a push-pull circuit 22 is overshot resulting from a property of an inductance element L1 by connecting the inductance element L1 between a trigger output circuit 21 and the push-pull circuit 22, when a transitor Q1 is changed from ON to OFF to lead the Vb of the circuit 22 up to a prescribed voltage. A laser current is led up quickly, since a gate voltage Vg is increased and an ON current is decreased in a power MOSFET 23 by the overshoot of the Vb. The light pulse of short pulse width is surely emitted thereby to enhance the distance measurement precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device for measuring a distance to an object by using a pulsed laser beam from a semiconductor laser to drive a semiconductor laser to emit a desired laser beam. To a light emitting circuit for a distance measuring device.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser emits a pulsed laser beam (hereinafter referred to as an "optical pulse"), and the optical pulse receives a reflected light which is reflected upon an object, thereby forming an optical pulse. 2. Description of the Related Art There is known a distance measuring device that measures a time from light emission to light reception and measures a distance to an object from the measured time. This type of distance measuring device is mounted on, for example, an automobile, measures the inter-vehicle distance with a preceding vehicle during traveling, and performs cruise control that controls the own vehicle speed so as to maintain an inter-vehicle distance proportional to the vehicle speed. It is used for various purposes, such as in control systems.

In the distance measuring apparatus as described above, if the measurable distance is to be made as long as possible, it is necessary to increase the light emission intensity from the semiconductor laser. Specifically, when the distance measuring device is used in the cruise control system, the distance between the vehicle and the preceding vehicle must be maintained at a predetermined distance.
It is necessary to detect the distance to the vehicle ahead. The emission intensity of the laser light required in this case is 1 even if the object is a reflector at the rear of the preceding vehicle and the beam size (divergence angle) of the laser light is reduced to 1 °.
A light emission intensity of 0 W or more is required.

The time difference between emission and reception of an optical pulse can be measured by various methods. For example, when the difference between the rise of an emitted light pulse and the rise of a received light pulse is measured. Although the rising timing of the light pulse at the time of light emission can be accurately detected, the rising timing of the light pulse at the time of light reception cannot be accurately detected, and as a result, there is a possibility that an error may occur in the measured distance from the actual distance. This means, for example,
A similar problem arises with other timing methods, such as comparing the falling times of the received light and measuring the time.

[0005] This is because the emitted light pulse is affected by light scattering in the air and contamination / reflection efficiency of the reflection surface of the object (hereinafter, these are collectively referred to as “disturbance”). This is because the emission intensity at the time does not show a strict pulse-like characteristic, but shows a disordered characteristic such as fluctuation with time or a decrease in the light receiving level. When such a disturbed light pulse is received, it is difficult to accurately determine which timing should be used as the rising timing (or falling timing), and an error occurs in the measurement result.

Incidentally, the measurement accuracy is usually limited to about 1/100 of the pulse width of the light pulse (that is, the light emission time per one light pulse). Therefore, in order to reduce the measurement error and perform the measurement with higher accuracy, it is necessary to make the pulse width of the optical pulse shorter. For example, in order to obtain the distance measurement accuracy of 10 cm or less, the pulse width needs to be about 50 n.
It must be less than sec.

By the way, as for the emission pattern of the semiconductor laser at the time of distance measurement, it is of course possible to emit one light pulse and measure the distance based on the light pulse (single light emission pulse). Although this is a general method that has been used in the past, such a measurement method using a single light emission pulse may cause the light pulse to be greatly disturbed or interrupted by the influence of disturbance between light emission and light reception. If the light cannot be received normally, the distance cannot be measured.

Therefore, as a method for making it hard to be affected by disturbance and capable of measuring a long distance, a pseudo-random noise code (hereinafter referred to as "P code") such as an M-sequence code (maximum period code sequence) is used.
There is also known a spread spectrum type distance measuring device for performing distance measurement using an "N code". That is, the light emission from the semiconductor laser is modulated by a PN code of a predetermined bit length (for example, light emission at the time of bit 1 and no light emission at the time of bit 0), and an optical pulse (strictly speaking, pulse width) matching the PN code. (A set of a plurality of different light pulses) is emitted toward the object.

In this method, by modulating the laser light with the PN code, it is hardly affected by disturbance and the measurement can be performed at a farther distance. , The cycle (chip rate) per bit (chip) of the PN code must be as short as possible.

[0010]

However, when trying to shorten the pulse width in order to increase the distance measurement accuracy,
On the contrary, the light emission intensity may be reduced due to the influence of the light emitting circuit for driving the semiconductor laser to emit light by energizing the semiconductor laser, and the measurable distance may be shortened. In the following,
A description will be given based on FIG. FIG. 8 is a circuit diagram showing a conventional semiconductor laser light emitting circuit.

As shown in FIG. 8, a conventional semiconductor laser light emitting circuit 80 emits a desired light pulse by controlling energization of a laser diode chip LD as a semiconductor laser. A laser diode 24 in which an LD is housed in a metal package 24a (not shown in FIG. 8, see FIG. 3 described later).
An n-channel power MOSFET 23 in which a MOSFET chip 23a is housed in a package (not shown) for turning on / off the energization of the laser diode 24 from the battery 25 (that is, energization of the laser diode chip LD); The NPN transistor Q1 is turned on / off in response to a light emission trigger signal input from a microcomputer (not shown) such as a microcomputer (not shown), so that the battery voltage (8V) of the battery 25 is changed via the resistor R3. A trigger output circuit 21 for outputting (in other words, boosting the light emission trigger signal to a predetermined voltage and outputting the same) and a gate drive for the power MOSFET 23 performed based on the output from the trigger output circuit 21 for further increasing the gate drive speed. , NPN transistors Q2 and P
Push-pull circuit 2 including NP-type transistor Q3
And 2.

In the trigger output circuit 21, a light emission trigger signal (eg, a 5V pulse) input from a microcomputer or the like is at a high level, and the 5V voltage is applied to the resistor R1.
While the voltage is applied to the base of the transistor Q1 via the transistor Q1, the transistor Q1 is turned on and the collector is electrically connected to the ground line (0 V). Therefore, the base voltage Vb of each of the transistors Q2 and Q3 of the push-pull circuit 22 becomes 0
V.

On the other hand, when the light emission trigger signal goes low, the transistor Q1 is turned off.
V will be applied to the push-pull circuit 22 via the resistor R3. The resistor R2 is a resistor for base bias of the transistor Q1, and the capacitor C1 is a so-called speed-up capacitor for increasing the switching speed of the transistor Q1.

The push-pull circuit 22 includes a power MOSF
This is a well-known circuit used to drive the gate of the ET 23 at high speed. The transistor Q2 has a collector connected to the positive electrode of the battery 25, and the collector has a collector connected to the battery 25.
As a complementary pair with the transistor Q3 connected to the negative side (ground line) of the transistor Q2. The bases and emitters of the transistors Q2 and Q3 are directly connected to each other. And each transistor Q2,
The base of Q3 (that is, the input terminal of the push-pull circuit 22) is connected to the collector of the transistor Q1 in the trigger output circuit 21, and the emitters of the transistors Q2 and Q3 (that is, the output terminals of the push-pull circuit 22) are power MOS.
The gate of the FET 23 (that is, the MOSFET chip 23a
Gate).

In order to cause the laser diode 24 to emit pulses at high speed, it is necessary to switch the power MOSFET 23 at high speed, and this switching speed is generally determined by the rising and falling speed of the gate voltage Vg. The rate of change of the gate voltage Vg mainly depends on the charge / discharge time constant determined by the input capacitance of the power MOSFET 23 and the resistance on the gate drive side.
In other words, since the power MOSFET 23 is turned on by charging the input capacitance to a desired gate voltage, it is necessary to charge and discharge the input capacitance at high speed in order to increase the switching speed of the power MOSFET 23.

Therefore, by driving the gate of the power MOSFET 23 through the push-pull circuit 22,
When the transistor Q1 of the trigger output circuit 21 is changed from on to off by the light emission trigger signal, the transistor Q2 is turned on, current is supplied from the battery 25 via the transistor Q2, and the input capacity of the power MOSFET 23 is rapidly charged. You.

Further, when the transistor Q1 of the trigger output circuit 21 changes from off to on due to the light emission trigger signal, the transistor Q2 turns off and the transistor Q3 turns on for a certain period. This is because when the transistor Q1 is turned on, the base of the transistor Q3 rapidly drops to the ground potential, whereas the power MOS
The gate charge does not rapidly discharge due to the influence of the time constant due to the input capacitance of the FET 23 and the resistor R4.
Is not suddenly lowered. When the transistor Q3 is turned on, the gate charge is rapidly discharged through the transistor Q3, and the transistor Q3 is turned off when the gate voltage is reduced by the discharge.

As described above, the gate is driven via the push-pull circuit 22 in order to rapidly charge and discharge the gate input capacitance of the power MOSFET 23 to increase the switching speed. Note that the capacitor C
2 is an energizing current of the laser diode 24 (laser current)
To prevent voltage fluctuation of the battery 25 caused by turning on and off the power MOSFET 23 at high speed. The battery 25 is always charged with a predetermined voltage (8 V). Functions as a power supply.

However, although the gate of the power MOSFET 23 can be driven at high speed by the push-pull circuit 22 to increase the switching speed as described above,
The output current of the power MOSFET 23 (that is, the laser current flowing through the laser diode 24) does not always reliably respond to the switching speed. The reason is that when the power MOSFET 23 is turned on and when the power MOSFET 23 is turned off, the power is turned off.
This is because the rise and fall of the laser current are delayed due to the influence of the parasitic inductance on the current supply path from the laser diode 2 to the laser diode 24.

This parasitic inductance is mainly caused by the wiring pattern length on the printed wiring board on which the semiconductor laser light emitting circuit 80 is formed, the lead wire of each part of the laser diode 24 or the power MOSFET 23, and the wire bonding inside the package. It is caused by

Of these, component wires such as parasitic inductances L11, L12 and L13 at the gate, source and drain terminals of the power MOSFET 23 and parasitic inductances L16 and L17 at the anode and cathode terminals of the laser diode 24, respectively. Parasitic inductance due to bonding and lead wires is a structural problem of the components themselves, so it is difficult for users who want to build circuits with off-the-shelf components to do anything.
It is difficult to get rid of.

Although the parasitic inductance (not shown) due to the wiring pattern length can be reduced to some extent by reducing the wiring pattern length by devising the component arrangement, the wiring pattern length is reduced to zero. Is physically impossible, so the parasitic inductance cannot be completely eliminated.

Therefore, no matter how fast the switching speed of the power MOSFET 23 is increased, a certain delay occurs in the rise and fall of the laser current on the output side. The power MOSFE is too much trying to shorten the pulse width of the light pulse.
If the on-period of T23 is set shorter than the rise time required for the laser current to completely rise (to reach a predetermined peak value), the fall starts before the laser current completely rises. The luminous intensity cannot be obtained, and the measurable distance becomes short.

On the other hand, the responsiveness of the output current of the power MOSFET 23 depends on the gate voltage value in addition to the various parasitic inductances present on the current path as described above.
In other words, the higher the gate voltage Vg, the higher the power MOSFET
Since the on-resistance of the laser diode 23 is reduced, the response speed of the laser current is correspondingly increased.

Therefore, it is conceivable that the rise and fall speed of the laser current, which is limited only by devising the component arrangement and the wiring pattern, can be realized by increasing the gate voltage when the power MOSFET 23 is turned on. Can be Specifically, for example, an on-resistance can be further reduced by separately providing a booster circuit for boosting a battery voltage to a desired voltage and applying the boosted voltage to a gate.

However, the method of increasing the gate voltage by providing a booster circuit or the like as described above naturally increases the number of components, resulting in an increase in the size and cost of the entire distance measuring device. In addition, noise or heat generation from the booster circuit may adversely affect the driving of the laser diode 24, and thus cannot be said to be a practical method.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in a distance measuring apparatus for measuring a distance to an object using a light pulse from a semiconductor laser, a light pulse having a short pulse width is surely emitted. It is intended to obtain a desired distance measurement accuracy.

[0028]

Means for Solving the Problems and Effects of the Invention The light emitting circuit according to claim 1 has been made to solve the above problems.
A distance measuring device that measures the distance to an object using pulsed laser light (light pulse) from a semiconductor laser, and emits laser light from the semiconductor laser. By turning on / off a MOSFET provided on a current supply path to the laser, a light pulse is emitted with a predetermined light emission intensity (light emission intensity corresponding to a current supplied from a DC power supply).

The switching operation of the MOSFET is performed based on a drive voltage input to the gate.
Specifically, the driving unit inputs a predetermined pulse signal to a push-pull circuit composed of an NPN transistor and a PNP transistor connected in series between the positive electrode side and the negative electrode side of the DC power supply. As a result, a drive voltage corresponding to the pulse signal is output from the output side of the push-pull circuit, and the gate of the MOSFET is driven.

Specifically, this push-pull circuit is, for example, an NP like a push-pull circuit 22 shown in FIG.
Connect the collector of the N-type transistor to the positive side of the DC power supply, PN
The collector of the P-type transistor is connected to the negative side of the DC power supply, the bases of the two are connected to each other, and a pulse signal from the driving means is input thereto. A so-called complementary SEP that outputs a drive voltage to the gate of a MOSFET
It can be configured as P (Single Ended Push-Pull).

Therefore, when a predetermined pulse signal is inputted to the push-pull circuit, a MOSF corresponding to the pulse signal is inputted.
An ET switching operation (for example, turning on a MOSFET when a pulse signal is at a high level) is performed, and a MOS
When the FET is turned on, the semiconductor laser emits light by supplying current from a DC power supply. That is, an optical pulse having a pulse width corresponding to the ON period of the MOSFET emits light.

In the light emitting circuit of the present invention, an inductance element is further connected to the input side of the push-pull circuit, and a pulse signal from the driving means is input to the push-pull circuit via the inductance element. . Here, in order to clarify the effect of connecting the inductance element as described above, the difference in the change in the gate voltage of the MOSFET between the case where the inductance element is not connected and the case where the inductance element is connected will be described with reference to FIG. FIG. 5 is an explanatory diagram showing changes in the input voltage of the push-pull circuit when the inductance element is not connected and when the inductance element is connected.

First, when no inductance element is connected, a pulse signal is directly input to the push-pull circuit. Therefore, when the pulse signal changes from the low level to the high level (for example, the same level as the power supply voltage of the push-pull circuit), the input voltage of the push-pull circuit (that is, the base voltage of each transistor) gradually increases as shown by the broken line in FIG. To reach the High level voltage value.

On the other hand, when the inductance element is connected as in the present invention, the pulse signal changes from the low level to the low level.
At the high level, due to the nature of the inductance element, as shown by the solid line in FIG. When the input voltage of the push-pull circuit reaches the High level voltage value of the pulse signal, the voltage does not stop rising immediately, and a so-called overshoot occurs.

As much as the overshoot occurs,
Since the input voltage of the push-pull circuit rises more than when there is no inductance element, overshoot occurs in the on-resistance of the NPN transistor turned on by this input voltage among the two transistors constituting the push-pull circuit. During this period, the on-resistance becomes smaller than that when no inductance element is provided. In other words, the ON voltage of the NPN transistor is smaller than that without the inductance element.

The driving voltage input to the gate of the MOSFET is substantially equal to the value obtained by subtracting the ON voltage (collector-emitter voltage at the time of ON) of the NPN transistor from the DC power supply voltage of the push-pull circuit. NPN due to overshoot by providing inductance element
The drive voltage increases as the ON voltage of the type transistor decreases.

That is, by providing the inductance element, the input voltage of the push-pull circuit at the time of inputting the pulse signal rises with a slight delay and the gate voltage of the MOSFET starts rising with that delay as compared with the case where the inductance element is not provided. The gate voltage of the MOSFET also increases due to the decrease in the on-resistance of the NPN transistor caused by the overshoot of the input voltage of the push-pull circuit.

As a result, the output current of the MOSFET (ie, the current flowing from the DC power supply for driving the semiconductor laser) has a slightly delayed start-up timing as compared with the case where there is no inductance element. As a result, the current rises to a current value (peak value) necessary for causing the semiconductor laser to emit light at a desired emission intensity.

Therefore, according to the light emitting circuit for a distance measuring device of the present invention (claim 1), the overshoot of the input voltage of the push-pull circuit by the inductance element causes M
Since the gate voltage of the OSFET increases and the conduction current of the semiconductor laser rises rapidly, an optical pulse having a short pulse width can be emitted reliably, and a desired distance measurement accuracy can be obtained.

The DC power supply for supplying current to the semiconductor laser and the DC power supply for the push-pull circuit may be common or may be provided separately. Here, the pulse signal input to the push-pull circuit may be, for example, a microcomputer used as a driving means, and a pulse signal may be directly output from the microcomputer, but in this case, the pulse signal is sent from the push-pull circuit to the gate of the MOSFET. It is necessary to output a voltage equal to or higher than a predetermined drive voltage to be input as a pulse signal from the microcomputer.
This is because the push-pull circuit is configured as an emitter follower, and the input voltage is output as it is as the output voltage.

For this reason, as shown in FIG. 8, for example, a battery voltage of 8 V is applied to a MOSFET through a push-pull circuit.
In order to input to the gate of T, it is necessary to input an 8 V pulse signal from the microcomputer to the push-pull circuit. However, most microcomputers that are generally used operate on a power supply voltage of 5 V, and it is generally difficult to directly output a voltage of 8 V from the microcomputer.

Therefore, for example, the driving means further includes an emitter connected to the negative electrode side of a DC power supply for supplying power to the push-pull circuit, and a collector connected to the DC power supply via a pull-up resistor. An NPN transistor connected to the positive terminal of the power supply and also connected to the input side of the push-pull circuit via an inductance element is provided. By turning on and off the NPN transistor, a pulse signal is transmitted through the inductance element. And input to the push-pull circuit.

That is, at least the output stage of the driving means is constituted by an NPN transistor as an open collector whose collector is pulled up to the positive side of the DC power supply of the push-pull circuit by a pull-up resistor. During the ON period of the NPN transistor, a pulse signal having the same potential (low level) as that of the negative electrode is input to the push-pull circuit when the collector is electrically connected to the negative electrode of the DC power supply. Does not operate, but when the NPN transistor is turned off, a voltage of 8 V of a DC power supply is input to the push-pull circuit via a pull-up resistor, and a voltage equivalent to the input voltage (high-level pulse signal) is applied to the push-pull circuit. M from circuit
It will be output to OSFET.

Therefore, according to the light emitting circuit for a distance measuring device according to the second aspect, the NPN provided at the output stage of the driving means is provided.
Since a pulse signal is generated by turning on / off the transistor, a pulse signal of a desired level can be output by controlling on / off of the NPN transistor with a 5 V logic signal from a microcomputer. Can be driven with a desired gate voltage by a control signal of a low level enough to control ON / OFF of the MOSFET.

By the way, in a distance measuring apparatus using an optical pulse from a semiconductor laser, the measurement is generally performed by measuring a time difference from the emission of the optical pulse to the reflection and reception of the object. Then, in the distance measurement, what kind of light pulse is emitted can be appropriately determined in consideration of the required measurable distance, the measurement accuracy, and the like, for example, by a single light emission pulse as described in the related art. It is of course possible to measure. However, a single emission pulse is easily affected by disturbance as described above, and it is difficult to measure a long distance.

Therefore, the driving means in the light emitting circuit according to the present invention is configured such that a pulse train composed of a plurality of pulses having different pulse widths is input to the push-pull circuit as a pulse signal. Good.
As a result, the MOSFET performs a switching operation according to the pulse train, and the semiconductor laser emits an optical pulse corresponding to the pulse train. That is, a plurality of light pulses having different pulse widths (light emission times) are emitted intermittently.

In this way, even if a part of the plurality of light pulses is affected by disturbance, the distance can be measured as long as other light pulses can be received normally. It is difficult to measure over longer distances. In this case, the number of the plurality of pulses constituting the pulse train and the width of each pulse are not particularly limited and can be determined as appropriate, but more preferably, for example, as described in claim 4, Random noise code (PN code)
It is good to make a pulse train according to. That is, the driving means generates a pseudo random noise code having a predetermined bit length synchronized with the reference clock, and inputs a pulse train corresponding to the pseudo random noise code to the push-pull circuit as a pulse signal.

The pseudo-random noise code is a well-known spreading code used to spread the spectrum of a transmission signal over a wide band in a spread spectrum communication system. If a pulse train corresponding to the pseudo random noise code is used as a pulse signal, as a result, an optical pulse modulated by the pseudo random noise code is emitted from the semiconductor laser. Then, the optical pulse reflected and received by the object is demodulated into the original pseudo-random noise code, the correlation value with the pseudo-random noise code at the time of light emission is obtained, and the time when the correlation value becomes maximum is detected. By doing so, the distance can be calculated.

As described above, in a light emitting circuit for a distance measuring device configured to emit a semiconductor laser using a pseudo-random noise code, a distance calculation is usually performed based on a correlation value. It is not easily received and has excellent interference resistance with other distance measuring devices. As the pseudo random noise code, for example, an M-sequence code or Gol
Although various examples such as a d-sequence code are given, in particular, an M-sequence code is
It is more preferable because the autocorrelation function exhibits excellent correlation characteristics such as a sharp peak every one period.

In the light emitting circuit for a distance measuring device according to the present invention, the semiconductor laser is housed in a metal package, and the metal package is a printed wiring board on which the light emitting circuit for the distance measuring device is formed. Is mounted on a ground pattern having the same potential as the negative electrode of the DC power supply in such a manner that heat generated from the semiconductor laser is radiated through the ground pattern.

Generally, the light conversion efficiency of a semiconductor laser is low (about 30%), and most of the power supplied from a DC power supply is emitted as heat. The semiconductor laser has such a property that the semiconductor laser is easily deteriorated as the temperature at the time of use is high.
Also, in the MOSFET, heat (switching loss) is generated by the ON / OFF operation, and this heat is
This has an adverse effect such as an increase in the on-resistance of the FET. Then, a vicious cycle may occur in which heat generation of the semiconductor laser and the MOSFET interact with each other to promote heat generation. Therefore, when using a semiconductor laser, care must be taken to ensure that heat is dissipated appropriately. On the other hand, in a printed wiring board, a ground pattern is usually formed as large as possible, and the entire surface of the substrate is often used as a ground pattern.

Therefore, the configuration is such that the semiconductor laser is housed in a metal package as described above, and the metal package is mounted on the ground pattern, so that at least heat generated from the semiconductor laser is generated via the metal package. Heat can be dissipated to the ground pattern. Then, depending on the component arrangement, heat generated by the MOSFET can be radiated to the ground pattern via the semiconductor laser. By enabling good heat dissipation from the semiconductor laser in this manner, a stable light pulse is obtained and the reliability of the semiconductor laser is increased.

The mounting of the metal package on the ground pattern may be performed, for example, via a heat radiating sheet or the like, or may be directly soldered if there is no electrical problem. The method is not particularly limited as long as good heat dissipation is possible and normal driving (light emission) of the semiconductor laser is possible.

The MOSFET may be connected to the positive side of the DC power supply of the semiconductor laser (so-called high-side switch) or connected to the negative side of the DC power supply (so-called low-side switch) in the current path of the semiconductor laser. , The MOSFET may be either an n-channel type or a p-channel type.
For example, as described in claim 6, the drain is connected to the positive electrode side of the DC power supply, the source is an n-channel power MOSFET connected to the anode of the semiconductor laser, the cathode of the semiconductor laser is connected to the negative electrode of the DC power supply And electrically connected to the metal package.

In this way, the heat generated from the semiconductor laser is favorably transmitted from the cathode to the metal package.
The heat radiation through the metal package is better performed.
In addition, since the cathode connected to the metal package is connected to the negative side of the DC power supply, the cathode and the metal package can be directly soldered to the ground pattern, and more favorable heat dissipation can be achieved.

[0056]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating a schematic configuration of an entire distance measuring device according to an embodiment to which the present invention is applied. As shown in FIG. 1, the distance measuring device 1 of the present embodiment
Is for measuring the distance to another vehicle traveling ahead mounted on an automobile, for example, and a reference clock oscillator 10 for generating a reference clock of a predetermined frequency (20 MHz in the present embodiment); An M-sequence emission trigger generation unit 11 that generates an M-sequence code having a predetermined bit length (31 bits in this embodiment) in synchronization with a clock and outputs a light emission trigger signal in which each bit value of the M-sequence code is inverted. And a laser beam whose amplitude is modulated by the emission trigger signal output from the M-sequence emission trigger generation unit 11 (emission intensity 1
(A light pulse of 0 W or more) toward the front of the vehicle.

The M-sequence light emission trigger generator 11 has a 31-bit (chip rate = 50 nsec.) M as shown in FIG.
It is provided with a 5-bit shift register or the like for generating a sequence code. Based on a control signal (generation start signal or generation stop signal of the M sequence code) from the microcomputer 14 described later, FIG. M-sequence code shown (High level:
5V). Then, an inverted version of each bit value of the generated M-sequence code (hereinafter also referred to as “inverted M-sequence”) is output as a light emission trigger signal.

The distance measuring device 1 of this embodiment is set so that when the vehicle speed becomes 40 km / h or more, the laser emission from the light emitting section 12 is started to measure the distance to the vehicle in front. Have been. Therefore, in the speed range of 40 km / h, a control signal is input from the microcomputer 14 to the M-sequence light emission trigger generation unit 11, and the output of the light emission trigger signal (and the light emission of the light pulse) is started.

The light emitting section 12 includes an M-sequence light emission trigger generating section 1
It emits a light pulse corresponding to the light emission trigger signal from No. 1 and has a specific configuration as shown in FIG. That is, as shown in FIG.
Means that the inductance element L1 is connected between the trigger output circuit 21 and the push-pull circuit, and that the laser diode 24
Except for being connected to the downstream side of 23, it is completely the same as the conventional semiconductor laser light emitting circuit 80 shown in FIG. Therefore, it basically operates similarly to the semiconductor laser light emitting circuit 80 of FIG. However, although the transitional operation is slightly different from that in FIG. 8 due to the provision of the inductance element L1, the details will be described later.

Further, the distance measuring device 1 of the present embodiment includes:
Light pulses emitted by the light emitting unit 12 toward the front of the vehicle (a plurality of light pulses having different pulse widths, which are output according to the inverted M series) hit the vehicle traveling ahead as an object and are reflected. A light receiving unit 16 having a photodiode or the like (not shown) for receiving light and outputting it as a voltage value, and an amplifier 1 for amplifying a light receiving signal from the light receiving unit 16
7 and the received light signal amplified by the amplifier 17 are compared with a preset reference voltage Vref. When the received light signal is higher than the reference voltage Vref, the signal goes high, and when the received light signal is lower than the reference voltage Vref, the signal goes low. Becomes 2
And a comparator 18 for outputting a value signal.

The binary signal output from the comparator 18 is input to a correlation value generator 19. Correlation value generator 19
Latches the inverted M-sequence (light-emission trigger signal) from the M-sequence light emission trigger generator 11 as a transmission code, and sequentially captures the binary signal output from the comparator 18 in synchronization with the reference clock (20 MHz). The received binary signal is latched as a reception code by the same bit length as the M-sequence code, and a correlation value between the latched transmission code and reception code is calculated. The correlation value calculated by the correlation value generator 19 is input to the peak detector 20 together with the calculation time obtained by counting the reference clock.

The calculation of the correlation value by the correlation value generation unit 19 is performed, for example, in such a manner that the bit value of each bit of the latched transmission / reception code coincides with that of the generally known spread spectrum type distance measuring device. When the correlation value is not
This is performed by calculating a correlation value such as "1" and a correlation value "1" when the bit values match, and calculating the sum of the correlation values obtained for each bit.

The peak detector 20 detects the time at which the correlation value input from the correlation value generator 19 becomes the maximum, and detects the detected time and the output time of the inverted M-sequence from the M-sequence light emission trigger generator 11. From this, the time required for the light pulse emitted from the light emitting unit 12 to hit the target object in front of the vehicle and be reflected (the round-trip time of the light pulse) is calculated. The measurement time obtained by the peak detector 20 is input to the microcomputer 14.

The microcomputer 14 includes a CPU, a ROM, and a RAM.
And outputs a control signal for controlling the generation of the M-sequence code to the M-sequence light emission trigger generator 11 while using the measurement time obtained by the peak detector 20 Calculate the inter-vehicle distance to the vehicle. And
The calculated inter-vehicle distance is output to, for example, a control device in the vehicle that requires inter-vehicle distance data, such as a cruise control system. The microcomputer 14 receives a vehicle speed signal from a vehicle speed sensor (not shown). When the vehicle speed exceeds 40 km / h, the microcomputer 14 outputs a measurement time request command to the peak detector 20. When receiving this command, the peak detector 20 outputs the measurement time to the microcomputer 14.

Next, with regard to the light emitting section 12 of the present embodiment,
A description will be given based on FIG. As described above, the provision of the inductance element L1 and the
8 is the same as that of the semiconductor laser light emitting circuit 80 of FIG. 8 except that the electrical connection between the power MOSFET 23 and the power MOSFET 23 is different. Therefore, the same components as those of FIG.

When a light emission trigger signal (inverted M-sequence) is input from the M-sequence light-emission trigger generating section 11, the transistor Q1 of the trigger output circuit 21 outputs the inverted M-sequence level "High".
Turns on / off according to “level” (5V) and “Low level” (0V). For this reason, the laser diode 24 emits a laser beam amplitude-modulated by the inverted M series as a light pulse. Note that the inverted M series and M
Since the sequence code is different from the sequence code only in that the logic is reversed, the amplitude modulation can be said to be the amplitude modulation by the M sequence code.

The inductance element L1 is a power MOS
The on-resistance is reduced by increasing the gate voltage of the FET 23, and the rising speed of the laser current is increased. Note that the inductance value of the inductance element L1 is several μH in this embodiment, and the parasitic inductances L11 to L13 of the power MOSFET 23 are different.
And the parasitic inductance L16, L of the laser diode 24.
17 is, for example, several nH, which is a sufficiently large value.

That is, in the conventional semiconductor laser light emitting circuit 80 without the inductance element L1, when the transistor Q1 of the trigger output circuit 21 changes from on to off, the input voltage of the push-pull circuit 22 has already been described with reference to FIG. (That is, the base voltage V of each transistor Q2, Q3
b) rises to a predetermined voltage (see the broken line in FIG. 5) and turns on the transistor Q2.

However, when the inductance element L1 is connected as in the present embodiment, when the transistor Q1 of the trigger output circuit 21 changes from on to off, the characteristic of the push-pull circuit 22 becomes similar to the characteristic shown by the solid line in FIG. Even if the input voltage (Vb) rises to a predetermined voltage, the voltage rise does not stop immediately, and an overshoot occurs due to the characteristic characteristic of the inductance.

During the occurrence of the overshoot, the on-resistance of the transistor Q2 is smaller than that of the conventional transistor without the inductance element L1, that is, the on-voltage is reduced. Therefore, the power MOSFE is supplied from the battery 25 via the transistor Q2.
The drive voltage (gate voltage V) input to the gate of T23
g) is because the on-voltage of the transistor Q2 is reduced.
It becomes larger than the case without the inductance element L1.
FIG. 6 shows a conventional case without the inductance element L1 and
The change of the gate voltage Vg and the change of the laser current in the case of the present embodiment in which the inductance element L1 is provided are shown. FIG. 6 shows the characteristics with respect to the input of the inverted M series.

As shown in FIG. 6B, the power MOSF
The gate voltage Vg of ET23 is equal to the inductance element L1.
When there is no voltage, the voltage is about 7 V. However, when the inductance element L1 is connected, the voltage rises to about 8 V, which is the battery voltage. Thus, the on-resistance of the power MOSFET 23 is reduced, and therefore, as shown in FIG. 6A, the laser current becomes larger than when the inductance element L1 is not provided.

Particularly effective is a case where a light pulse having a short pulse width is emitted. That is, as shown in FIG. 6A, in the conventional case without the inductance element L1, in the case of the pulse C having a long pulse width, although there is a certain time delay from the start of the rising to the complete rising, the distance measurement is not performed. In order to reach a required peak value, a light pulse can be emitted at a desired emission intensity. However, in the case of the pulse A or the pulse B having a short pulse width, the laser current starts to fall without completely rising, that is, before reaching a desired peak value.

This is, as described above, a power MOSFET.
The parasitic inductances L11, L12, L13 of the laser diode 24 and the parasitic inductances L16, L16,
L17, and also due to the influence of the parasitic inductance of the current path from the battery 25 and the capacitor C2 to the laser diode 24.

On the other hand, when the inductance element L1 is connected, the pulse C having a long pulse width reaches not only a desired peak value but also a current value equal to or higher than the desired peak value due to the effect of overshoot. For,
There is no problem from the viewpoint of obtaining a desired emission intensity. Also, in the case of the pulse A or the pulse B having a short pulse width, the pulse reaches the desired peak value without fail. This is because the gate voltage Vg increases due to the overshoot of the input voltage of the push-pull circuit 22 and the power MOS
This is realized by reducing the on-resistance of the FET 23.

As a result, as shown in FIG. 7, the light emission intensity of the light pulse by the pulse A and the pulse B having a short pulse width is:
In the case of the related art without the inductance element L1, a desired light emission intensity (10 W) cannot be obtained, and the measurable distance becomes short. Emission intensity has been reached.

Next, the mounting of the laser diode 24 on a printed circuit board will be described with reference to FIGS. FIG. 3 shows a laser diode 24 and a power MOSF.
Explanatory drawing (perspective view) showing a state in which the ET 23 and various components connected thereto are mounted on the printed wiring board 31.
It is.

The laser diode 24 is a well-known semiconductor light-emitting device that uses a semiconductor as an optical amplification medium and can obtain laser oscillation by current injection. The laser diode chip (corresponding to the semiconductor laser of the present invention) LD is a metal package 2.
4a. And three lead wires 24b, 2
4c and 24d, the anode lead wire 24c is connected to the laser diode chip L inside the metal package 24a.
It is connected to the anode of D by wire bonding. In addition, the cathode lead wire 24b is connected to the cathode of the laser diode chip LD by wire bonding inside the metal package 24a, and is also directly connected to the metal package 24a itself to be electrically connected to each other. Has become.

The other lead wire 24d other than the lead wires 24b and 24c is generally used to hold the metal package 24a at the ground potential, and is made of the same metal as the cathode lead wire 24b. It is directly connected (electrically conductive) to the package 24a. Therefore, the lead wire 24d also substantially functions as a cathode and is connected to the ground pattern 32 (and 32a).

On the printed wiring board 31, wiring patterns such as the wiring patterns 33a to 33f and other wiring patterns (not shown) necessary for forming the circuit of the light emitting section 12 are formed on the front surface, and the ground pattern 32 is formed on the entire back surface. Have been. Note that a ground pattern 32a is also partially formed on the surface. Then, each of the wiring patterns 33a to 33
f and a predetermined position on the ground pattern 32a, the power MOSFET 23, the capacitor C2, the transistor Q
Various components such as 2 and Q3 are mounted by soldering.

In the present embodiment, as shown in FIG. 2, the power MOSFET 23 is provided as a so-called high-side switch in an energizing path of the laser diode 24, and the source of the power MOSFET 23 is connected to the anode of the laser diode 24. The cathode of 24 is connected to the negative electrode side (ground line) of the battery 25. Therefore, the laser diode 24
The printed wiring board 31 is mounted on the back surface on which the ground pattern 32 is formed.

Then, both the cathode lead 24b and the lead 24d are connected to the ground pattern 32 (and 32
The metal package 24a is, of course, soldered directly to the ground pattern 32 as well as soldered to a). Thereby, heat generated from the laser diode chip LD is radiated to the ground pattern 32 via the lead wires 24b and 24d and the metal package 24a.

As described in detail above, in the light emitting section 12 of the distance measuring device 1 of the present embodiment, the inductance element L1 is connected between the trigger output circuit 21 and the push-pull circuit 22 so that the inductance element L1 The input voltage (Vb) of the push-pull circuit 22 is increased by utilizing the overshoot caused by the property, and the power MOS
The gate voltage Vg of the FET 23 is increased. As a result, the on-resistance of the power MOSFET 23 decreases, and the laser current can rise at a high speed.

Further, the laser diode 24 is connected to the downstream side of the power MOSFET 23 in the current path, and the cathode is connected to the ground line. In addition, since the metal package 24a containing the laser diode chip LD is connected to the cathode lead 24b, the laser diode 24
a can also be soldered to the ground pattern 32 on the printed wiring board 31 as it is.

Therefore, according to the distance measuring apparatus 1 of the present embodiment, a light pulse having a short pulse width can be reliably emitted, and a desired distance measuring accuracy can be obtained. Further, since the light emission trigger signal is input to the push-pull circuit 22 via the trigger output circuit 21, the power MOSFET 23 has an M-sequence code (inverted M-sequence) lower in level than the output voltage of the push-pull circuit 22. Gate drive can be controlled.

Since the laser current can be quickly raised by the inductance element L1, the laser diode 2 based on the M-sequence code having a small chip rate (for example, 50 nsec. As in the present embodiment) is used.
4 can emit light with a desired emission intensity. This makes it possible to further enhance the accuracy of distance measurement by the spread spectrum method having excellent noise resistance performance.

Further, by arranging the metal package 24a in a circuit configuration and component arrangement that can be directly soldered to the ground pattern 32, better heat dissipation from the laser diode 24 and the power MOSFET 23 connected thereto becomes possible. The high-speed switching of the power MOSFET 23 is further stabilized, a stable light pulse is obtained, and the reliability of the laser diode 24 is further improved.

Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. In the present embodiment, the light emitting unit 12 (excluding the laser diode 24) and M
The sequence light emission trigger generation unit 11 constitutes a light emitting circuit for distance measurement of the present invention. Among them, the driving means of the present invention is realized by the M sequence light emission trigger generation unit 11 and the trigger output circuit 21, and the transistor Q1 is provided by the present invention. The driving means corresponds to an NPN transistor, and the resistor R3 corresponds to a pull-up resistor of the present invention. The battery 25 corresponds to the DC power supply of the present invention, and the output from the trigger output circuit 21 to the push-pull circuit 22 (that is, the collector output voltage of the transistor Q1) corresponds to the pulse signal of the present invention. A signal output from the trigger output circuit 21 to the push-pull circuit 22 in a sequence corresponds to a pulse train of the present invention.

The embodiments of the present invention are not limited to the above-described embodiments at all, and it goes without saying that various forms can be adopted as long as they fall within the technical scope of the present invention. For example, in the above embodiment, the transistor constituting the trigger output circuit 21 is only the transistor Q1, but the transistors are connected in two stages (the transistor Q1).
A so-called open-collector TTL in which another transistor is connected before the first stage) may be configured. In this case, since the level change of the light emission trigger signal is output as it is to the push-pull circuit 22 in the positive logic, the M sequence light emission trigger generation unit 11 may just output the signal without inverting the M sequence code.

In the above embodiment, the M-sequence code is used as the pseudo-random noise code. However, the present invention is not limited to this, and another PN code such as a Gold code may be used.
However, considering that the autocorrelation function of the M sequence exhibits excellent peak characteristics, it is preferable to use the M sequence code.

Further, in the above embodiment, the mounting of the laser diode 24 on the printed wiring board 31 is such that the metal package 24a is directly soldered to the ground pattern 32. However, the mounting is not limited to such a direct mounting. For example, the ground pattern 3 via a silicon heat dissipation sheet or the like
2 may be mounted so as to be in close contact therewith, and various mounting methods may be employed as long as the heat of the metal package 24a (and, consequently, the heat generated from the laser diode chip LD) can be radiated well to the ground pattern 32. it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a schematic configuration of an entire distance measuring apparatus according to an embodiment.

FIG. 2 is an electric circuit diagram showing a light emitting unit of the embodiment.

FIG. 3 is an explanatory view (perspective view) showing how a laser diode, a power MOSFET, and various components connected to the laser diode are mounted on a printed wiring board.

FIG. 4 is an explanatory diagram illustrating an M-sequence code according to the present embodiment.

FIG. 5 is an explanatory diagram showing a change in input voltage of a push-pull circuit when an inductance element is not connected and when an inductance element is connected.

FIGS. 6A and 6B are explanatory diagrams showing a difference between a case where an inductance element is provided and a case where an inductance element is not provided, and FIG. 6A is a diagram showing laser current characteristics and FIG.
Indicates the gate voltage characteristics of the power MOSFET.

FIG. 7 is an explanatory diagram showing a difference in light emission intensity of a light pulse between a case where an inductance element is provided and a case where an inductance element is not provided.

FIG. 8 is an electric circuit diagram showing a conventional semiconductor laser light emitting circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 10 ... Reference clock oscillator, 11 ...
M-sequence light emission trigger generator, 12 ... light emitter, 14 ... microcomputer, 16 ... light receiver, 17 ... amplifier, 18 ...
Comparator, 19: Correlation value generator, 20: Peak detector, 21: Trigger output circuit, 22: Push-pull circuit,
23: Power MOSFET, 23a: MOSFET chip, 24: Laser diode, 24a: Metal package, 24b: Cathode lead wire, 24c: Anode lead wire, 24d: Lead wire, 25: Battery, 31: Printed wiring board, 32, 32a: Ground pattern, 33
a to 33f: wiring pattern, 80: semiconductor laser light emitting circuit, C1, C2: capacitor, L11 to L13, L16, L17
... parasitic inductance, L1 ... inductance element, L
D: laser diode chip, Q1, Q2, Q3: transistor, R1 to R4: resistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F112 AD01 BA03 BA06 BA07 CA12 EA03 EA20 5F073 BA09 EA17 EA29 FA05 FA30 GA04 GA12 GA16 GA18 5J084 AA05 AB01 AC02 AD01 BA04 BA36 CA03 CA10 CA23 CA52 CA53 CA55 CA57 CA69 DA10 EA04 A07 AA18 CA65 FA20 HA08 HA10 HA19 HA25 HA29 HA33 HA44 KA00 KA32 KA33 KA47 KA66 MA21 QA04 SA15 TA01 TA06 UW09

Claims (6)

[Claims] 1. A light emitting circuit provided in a distance measuring device for measuring a distance to an object using a pulsed laser light from a semiconductor laser, and for emitting the laser light from the semiconductor laser, A MOSFET provided on a current supply path from the DC power supply to the semiconductor laser, and an NP connected in series between a positive electrode side and a negative electrode side of the DC power supply.
A push-pull circuit composed of an N-type transistor and a PNP-type transistor; and a predetermined pulse signal input to the push-pull circuit;
A driving means for outputting a driving voltage according to the pulse signal from an output side of the push-pull circuit to a gate of the MOSFET, further comprising an inductance element connected to an input side of the push-pull circuit; A light emitting circuit for a distance measuring device, wherein a signal is input to the push-pull circuit via the inductance element. 2. The driving means further includes an emitter connected to a negative pole of a DC power supply for supplying power to the push-pull circuit, and a collector connected to a positive pole of the DC power supply via a pull-up resistor. And an NPN transistor connected to the input side of the push-pull circuit via the inductance element, by turning on / off the NPN transistor.
The pulse signal is input to the push-pull circuit via the inductance element.
A light emitting circuit for a distance measuring device as described in the above. 3. A light emitting device for a distance measuring device according to claim 1, wherein said driving means inputs a pulse train composed of a plurality of pulses having different pulse widths to said push-pull circuit as said pulse signal. circuit 4. The driving means generates a pseudo-random noise code having a predetermined bit length in synchronization with a reference clock, and inputs the pulse train corresponding to the pseudo-random noise code to the push-pull circuit. The light emitting circuit for a distance measuring device according to claim 3. 5. The semiconductor laser is housed in a metal package, and the metal package has a ground pattern having the same potential as a negative electrode of a DC power supply on a printed circuit board on which the light emitting circuit for the distance measuring device is formed. The light emitting circuit for a distance measuring device according to any one of claims 1 to 4, wherein the light emitting circuit is mounted on the semiconductor laser so that heat generated from the semiconductor laser is radiated through the ground pattern. 6. The MOSFET is an n-channel power MOSFET having a drain connected to a positive electrode of a DC power supply and a source connected to an anode of the semiconductor laser. A cathode of the semiconductor laser is connected to a negative electrode of the DC power supply. 6. The light emitting circuit for a distance measuring device according to claim 5, wherein the light emitting circuit is connected to and electrically connected to the metal package.