Electronic circuit and laser scanner

Abstract

The invention relates to an electronic circuit and a laser scanner. A laser scanner (2) and an electronic circuit (1) for generating laser pulses for the laser scanner, the electronic circuit comprising: an input contact (3) for inputting a voltage; a series circuit connected to the input contacts, comprising at least one coil (L1) and at least one first diode (D1), the first diode being connected in a positive conduction direction of the input voltage, at least one switching element (Q1) being connected to the series circuit, by means of which switching element a switching path is formed, a laser trigger signal (12) can be applied to the gate of the switching element, at least one anti-parallel circuit comprising a laser diode (LD) and a second diode (D2) is connected at one end to the cathode of the first diode and the switching element and at the other end to at least one first capacitor (C1), and the first capacitor is grounded at the other end, optical laser pulses can be generated on the laser diode by means of the laser trigger signal.

Description

[0001] The invention relates to an electronic circuit for generating laser pulses for a laser scanner according to the preamble of claim 1 and to a laser scanner according to the preamble of claim 13 .

[0002] Typically, existing solutions either provide circuits that are highly fault-tolerant with regard to laser class 1 classification, eye safety and unwanted laser emissions due to component failures, or circuits that are more energy-efficient, i.e. the ratio of the input power of the power supply to the laser diode. For low-power laser diodes, low energy efficiency is usually acceptable. In newer sensor applications using highly modern high-power laser diodes, low energy efficiency of the driver circuit can increase the total power consumption of the sensor by about 30-40%. On the other hand, known solutions for more energy-efficient laser driver circuits are significantly more susceptible to component failures, which lead to unwanted laser emissions and thus a high probability of violating the limit values ​​of laser class 1. In order to prevent this, more suitable safety identification mechanisms are required, which leads to increased system complexity and increased manufacturing costs.

[0003] The present invention provides a solution for an energy efficient and highly fault tolerant laser driving circuit to overcome this design compromise.

[0004] The basic concepts of common laser drive circuits are described below:

[0005] Figure 1 A high-side driver solution according to the prior art is shown. In this concept, a high-side switching element is used to direct the current through the laser diode. Both integrated and discrete solutions are possible here. A short circuit of the driver switching element leads directly to undesired laser emission. The pulse width of the trigger signal also directly affects the emission time. Comprehensive detection mechanisms are required inside the driver to ensure that laser class 1 is achieved.

[0006] Figure 2 A resonant capacitor discharge laser driver according to the prior art is shown. A widely used and commonly used laser driver circuit is based on a resonant design, comprising a capacitor, a laser diode and a low-side switching element. Field effect transistors are usually used. The capacitor is charged and stores energy, usually for a single laser pulse. To emit the laser, the switching element is closed and the charge of the capacitor is conducted through the laser diode. The loop inductance of the current loop forms an oscillating circuit with the capacitor, thereby defining the pulse shape.

[0007] A simple and fault-tolerant method of charging the capacitor is to use a resistor between the input power supply and the capacitor. Since the capacitor is almost completely discharged at each shot, the efficiency when charging is always around 50%. This concept is still susceptible to short-circuit failures of the switching elements. Although the current flow is limited by the resistor, undesired laser firing is still possible due to component failure. In practice, many different concepts are used for the pre-charging and arrangement of these components.

[0008] Figure 3 An improved low-side driver design based on a single transistor avalanche pulse design according to the prior art is shown. To prevent unwanted lasing in the event of a short circuit of the switching element, a capacitor is pre-charged on the cathode side of the laser diode instead of the anode side.

[0009] In this concept, abnormal component failures cannot lead to undesired laser emission. The only possibilities for violating the limit values ​​of laser class 1 are wrong input supply voltage and wrong laser trigger signals, such as wrong pulse width and / or wrong repetition time. The additional diode in this circuit is optional. This diode is used to prevent undesired ringing effects and has no general function in terms of precharging or laser emission.

[0010] Figure 4 A resonant laser driver with a high-side boost circuit according to the prior art is shown.

[0011] Another concept is to use a boost converter topology as a charging circuit. An inductor, a diode and an additional transistor are added. For precharging, the additional transistor is closed for a defined time. The time defines the voltage to which the capacitor is charged. After the transistor is turned on, the energy stored in the inductor is amplified in the capacitor by the added diode. At the cathode of the laser diode, an additional voltage is required to prevent current from flowing through the laser diode at this time in order to charge the drain-source capacitance of the transistor. The input voltage is designed to keep it below the threshold to prevent laser emission in the event of a short circuit in the switching element. However, this concept is very susceptible to inaccuracies in the timing of the charging signal, especially due to component tolerances. Therefore, it can be considered that fast-responding safety detection mechanisms are required for laser class 1 applications.

[0012] An extension of this solution is the patent family around patent US9368936, which does not require the additional transistor described and, due to the adopted topology, achieves an almost constant input voltage multiplication with high efficiency while being less susceptible to timing and component tolerances. However, a disadvantage of this solution is that without elaborate additional identification mechanisms, even a simple component failure of a switching element may lead to undesired laser emission and a violation of eye safety. Other concepts are also described in patents US11075502B2, US11631961B2 and US10673204B2, which describe other possible circuits and solutions for driver circuits for laser diodes in pulsed laser applications.

[0013] Typically, existing solutions use highly fault-tolerant concepts with regard to eye safety and unwanted laser emissions due to component failures. Typically, existing solutions also have low energy efficiency with regard to the input power from the power supply to the laser diode. Other solutions use circuits with higher energy efficiency, but are also more prone to component failures, so the need for safety identification mechanisms increases. The various disadvantages of currently known solutions have been explained above. In addition, most high-performance applications require high input supply voltages, such as greater than 60 volts, so additional measures are needed to meet electrical safety standards within the overall system.

[0014] US2021 / 0333362 A1 also discloses a light-emitting device. The light-emitting device includes at least two laser emission circuits, each of which includes a power supply, a laser emitter, an energy storage circuit, and a control circuit; in each laser emission circuit, the control circuit is configured so that it connects the energy storage circuit and the power supply in the laser emission circuit in a first time period, so that the power supply can store energy in the energy storage circuit; the control circuit is also configured so that it connects the laser emitter and the energy storage circuit in the laser emission circuit in a second time period, so that the energy storage circuit supplies power to the laser emitter to enable the laser emitter to emit an optical pulse signal; and two or more laser emission circuits share a power supply.

[0015] The object of the present invention is to provide an improved, highly fault-tolerant driver circuit for laser diodes in pulsed laser applications with pulse widths of a few nanoseconds and with constantly high pulse energies at high peak currents.

[0016] This task is achieved according to claim 1 by an electronic circuit for generating laser pulses for a laser scanner, the electronic circuit comprising: an input contact for an input voltage; a series circuit connected to the input contact, the series circuit comprising at least one coil and at least one first diode, wherein the first diode is connected in the forward conduction direction of the input voltage, wherein at least one switching element connected to the series circuit is arranged, wherein a switching path is formed with the aid of the switching element, wherein a laser trigger signal can be applied to the gate of the switching element, wherein at least one anti-parallel circuit including a laser diode and a second diode is connected at one end to the cathode of the first diode and the switching element, wherein the anti-parallel circuit of the laser diode and the second diode is connected at the other end to at least one first capacitor, and the first capacitor is grounded at the other end, wherein an optical laser pulse can be generated at the laser diode by the laser trigger signal at the switching element.

[0017] After startup and application of voltage at the input contacts, the input voltage at the input contacts charges the first capacitor via the coil, the first diode, and the second diode.

[0018] The first capacitor is a single capacitor or a series of capacitors in order to buffer the energy required for a single laser shot.

[0019] For example, the switching element is a switching element with very fast switching times, which is able to carry high peak currents and withstand high charging voltages during laser pulses. The switching element is controlled by an external laser trigger signal or a control signal at the control signal input. Preferably, a low-side driver is provided to drive the gate of the switching element used. When the external laser trigger signal is activated, the switching element is turned on only for a very limited time.

[0020] During the first pulse of the laser trigger signal, starting from the first time point, the first capacitor is fully discharged through the laser diode and the switching element, and the first lower laser pulse is generated. At this time, the voltage level of the cathode of the laser diode (corresponding to the drain terminal of the switching element) is the same as the ground reference, which causes the voltage drop from the first capacitor to the switching element to be equal to the input voltage. Current begins to flow through the coil and the first diode.

[0021] After the switching element is closed, the current through the coil and the first diode continues to increase and charges the first capacitor to the voltage of the second diode until the voltage level at the cathode of the laser diode reaches the magnitude of the input voltage at a second point in time and is now at the same voltage level as the input voltage. From now on, the current through the coil decreases until it reaches 0 amperes again at a third point in time. During this time, the first capacitor is still charged to a voltage level that is almost twice the input voltage.

[0022] After the third time point, the first diode prevents negative current from flowing through the coil, so that the first capacitor does not discharge through the laser diode and the coil. Under real conditions, only slight oscillations remain, but this does not lead to undesired illumination of the laser diode. The first capacitor stores energy for the next laser pulse with a charging voltage that is almost twice the input voltage until the laser trigger signal triggers the circuit again at the fourth time point.

[0023] In particular, compared to patent application US2021 / 0333362 A1, there is a fundamental difference in the concept of how the switching element according to the invention is used. In a resonant laser driver with a high-side boost circuit and a conventional boost converter circuit, the switching element is closed for the time required to increase the current through the inductor and the switching element to increase the magnetic field in the inductor to a certain value, thereby achieving a charging voltage that is a multiple of the input voltage. By varying the time the switching element is closed, the charge stored at the first capacitor or the charging voltage can be controlled.

[0024] However, in the present invention, the switching element is closed only for a limited time, in particular an extremely limited time, i.e. a few nanoseconds, to release the laser pulse. During this time, no significant current can be established through the inductor and the switching element. But the very short time that the switching element is closed is sufficient to bring the voltage level at the cathode of the laser diode close to 0 volts and start the above-mentioned charging current. As long as the switching element is not closed for a long time, the voltage at the first capacitor after charging is almost twice the input voltage, regardless of when the switching element is closed. On the one hand, this means that with the closing time of the switching element, the possibility of directly controlling the charging voltage is lost. On the other hand, it is impossible to generate a voltage higher than twice the input voltage, so the maximum energy of each pulse is completely predictable. No additional safety mechanisms, such as high-speed voltage measurement, are required. And the energy of each pulse can still be controlled by changing the input supply voltage, which can be measured by relatively slow voltage measurement.

[0025] To further increase the sensitivity to erroneous pulse widths of the laser trigger signal, a coil or inductor can be used, where the peak charging current through the coil is close to the saturation current of the inductor type. Even if the pulse width of the laser trigger signal is too large, the coil or inductor cannot store more magnetic energy, thus preventing overloading of the first capacitor. In addition, the current through the coil rises quickly, and an easily implementable power switch can recognize this fault condition.

[0026] The laser diode is, for example, a 5J VCSEL laser diode or a multi-channel edge emitter.

[0027] The main advantages of the present invention are as follows:

[0028] The charging efficiency is as high as 97%, compared to the 50% of the commonly used RC charging circuit. The overall efficiency, i.e. the ratio of electrical input power to optical output power, depends on the charging efficiency, the power conversion efficiency of the laser diode and the discharge efficiency (mainly defined by the losses in the switching elements used).

[0029] In the case of typical component failures (e.g., short circuits in switching elements), no harmful laser emissions will occur, so no safety identification mechanisms are required within the laser driver circuit. The integrity of the incoming input power and laser trigger signals must be ensured at the respective modules that generate them. Hazardous laser emissions will only occur if the input signals are incorrect, i.e., if there is an incorrect supply voltage or an incorrect laser trigger signal.

[0030] A robust system against insufficient pulse width accuracy of the laser trigger signal is provided.

[0031] There is no non-critical minimum pulse width and no non-critical turn-off behavior of the switching element.

[0032] Only a relatively low input voltage is required compared to the peak voltage required to produce the laser shot. The high voltage is limited by the laser driver circuit, making it easier to meet electrical safety standards.

[0033] Generates stable, repeatable pulse shapes with constant pulse energy.

[0034] In one embodiment of the invention, at least one second capacitor connected in parallel to the input contact is arranged.

[0035] The second capacitor is a capacitor or, for example, a plurality of bulk capacitors having a capacitance that is much greater than the first capacitor, in order to achieve a sufficient stabilization of the input voltage at the input contact.

[0036] In one embodiment of the invention, the switching element is in particular a switching transistor, in particular a field effect transistor, very particularly a gallium nitride field effect transistor.

[0037] In contrast to the current-controlled bipolar transistor, the field-effect transistor is a voltage-controlled circuit element. Control is via a gate-source voltage, which is used to adjust the channel cross-section or charge carrier density, i.e. the semiconductor resistance, in order to switch or control the current intensity.

[0038] Field effect transistors are particularly suitable for switching large currents. GaN field effect transistors are very suitable for switching large currents.

[0039] In a further development of the invention, the laser trigger signal is generated by a low-side FET driver. A low-side FET driver is an integrated electronic circuit that drives a power switch, ie a switching element.

[0040] A transistor driver or low-side FET driver is a circuit that provides the necessary voltage to switch a transistor on or off within the required time. Here, it is usually an amplifier with an additional level shifter. This allows large loads, such as field effect transistors, to be switched with a logic output that usually operates at 5V or 3.3V. The driver can operate in analog or digital mode.

[0041] During the first pulse of the laser trigger signal, starting from a first point in time, the first capacitor is completely discharged through the laser diode and the switching element and a first lower laser pulse is generated. At this time, the voltage level of the cathode of the laser diode is the same as the ground reference, which results in a voltage drop from the second capacitor to the switching element equal to the input voltage. If the pulse width of the laser trigger signal is selected to be longer than the calculated laser pulse width, a complete discharge of the first capacitor is ensured.

[0042] In one embodiment of the invention, the capacitance of the second capacitor is at least 500 times greater, in particular 1000 times greater, than the capacitance of the first capacitor in order to achieve a sufficient stabilization of the input voltage at the input contact.

[0043] In one embodiment of the invention, the switching element is closed by the laser trigger signal for only 5 nanoseconds to 50 nanoseconds, in particular 15 nanoseconds to 20 nanoseconds, in order to release the laser pulse at the laser diode.

[0044] A further development relates to a driver circuit for a laser diode in pulsed laser applications, in which the pulse width is a few nanoseconds, in particular 5 ns to 30 ns, and the pulse energy is high, for example a few microjoules per laser shot, and high peak currents, for example currents of more than 100 amperes, are used.

[0045] The switching element is closed only for an extremely limited time, i.e. a few nanoseconds, to release the laser pulse. During this time, no significant current can be built up through the inductor and the switching element. But the very short time that the switching element is closed is enough to bring the voltage level at the cathode of the laser diode close to 0 V and start the above-mentioned charging current. As long as the switching element is not closed for too long, the voltage at the capacitor after charging is almost twice the input voltage, regardless of when the switching element is closed. On the one hand, this means that the possibility of directly controlling the charging voltage is lost with the closing time of the switching element. On the other hand, it is not possible to generate voltages higher than twice the input voltage, so the maximum energy of each pulse is completely predictable. No additional safety mechanisms, such as high-speed voltage measurements, are required. And the energy of each pulse can still be controlled by varying the input supply voltage, which can be measured by relatively slow voltage measurements.

[0046] In a development of the invention, the energy of each laser pulse is set by controlling the input supply voltage.

[0047] The energy of each laser pulse can therefore be set or controlled or regulated simply by means of the input supply voltage used.

[0048] In a refinement of the invention, the energy of each laser pulse is not set by varying the pulse width of the laser trigger signal.

[0049] In one embodiment of the invention, the first capacitor, the laser diode and the switching element form a resonant discharge laser driver.

[0050] The extended scheme utilizes the principle of resonant capacitor discharge laser driver and includes capacitor, laser diode and switching element. However, unlike the conventional solution, the charging circuit is connected to the cathode side of the laser driver, while the capacitor is still connected to the anode. In order to achieve current flow for charging, an anti-parallel diode is added. With this change, the critical failure of short-circuiting the switching element is overcome.

[0051] In a further development of the invention, the coil, the first diode and the switching element form a step-up converter circuit, wherein the switching element is closed only for a limited time, so that due to the circuit a voltage is generated which depends only on the input voltage and is therefore deterministic and corresponds to almost twice the input voltage.

[0052] In order to overcome the relatively low efficiency of 50% of the commonly used charging resistor, a circuit with a common boost converter topology is used, which includes an inductor, a diode and a transistor. A high-speed switching element of an oscillating drive loop is used, wherein the high-speed switching element is closed only for a limited time, in particular a very limited time, so that due to the circuit, a voltage that depends only on the input voltage and is therefore deterministic is generated, which voltage is almost equivalent to twice the input voltage.

[0053] According to one embodiment, the switching element is closed by the laser trigger signal for, for example, only 5 nanoseconds to 50 nanoseconds, in particular 15 nanoseconds to 20 nanoseconds, in order to release the laser pulse at the laser diode.

[0054] In an extension of the invention, an antiparallel circuit of a laser diode and a second diode is connected in parallel with a further antiparallel circuit of a laser diode and a diode, wherein the antiparallel circuits are each connected to at least one further capacitor and the capacitor is grounded at the other end, wherein optical laser pulses can be generated simultaneously at all laser diodes via a laser trigger signal at the switching element.

[0055] In one embodiment of the invention, the laser diodes are arranged in a common housing or on a common substrate.

[0056] This object is also achieved according to claim 13 by a laser scanner having an electronic circuit according to claim 1. The laser scanner has at least one transmitting element and at least one receiving element and a control and evaluation unit for evaluating the light flight time of a light beam from the transmitting element via the object to the receiving element. The transmitting element has a laser diode.

[0057] In an extension of the invention, the laser scanner comprises at least one transmitting element and at least one receiving element and a control and evaluation unit for evaluating the light flight time of the light beam from the transmitting element via the object to the receiving element. Here, a plurality of transmitting elements and a plurality of receiving elements are arranged in a common housing, wherein the light beam is emitted and / or received in a fan-shaped manner in different angular directions, wherein the distance of the emitted light beam of the transmitting element increases with increasing distance from the laser scanner and / or the distance of the received light beam of the receiving element decreases with decreasing distance from the laser scanner. For example, the transmitting elements and the receiving elements are arranged in a row. The angular deflection can be achieved by an optical device.

[0058] A preferred application is the use of the electronic circuit in a laser class 1 solid-state flash lidar sensor.

[0059] According to the extended solution, the light beam is emitted or received in a fan shape in different angular directions, whereby the monitoring area can be easily checked to determine whether an object is present in the monitoring area and at which position, i.e. at what distance the object is located. In addition, objects can be measured, or surrounding contours and their changes can be detected. By fan-shaped emission or fan-shaped reception of the light beam, the monitoring area is monitored in the fan-shaped plane. The laser scanner can be manufactured with high angular accuracy because the transmitting element and the receiving element are firmly fixed and the light beam reaches the monitoring area directly without moving parts. This ensures that each laser scanner complies with the specific required minimum angular accuracy.

[0060] Therefore, the laser scanner has a simple and economical structure. Since the laser scanner has no mechanically movable parts, there is no mechanical wear and tear, and the service life is long. For example, the use of the laser scanner according to the present invention can meet the required service life of, for example, about 20 years.

[0061] Since the laser scanner does not require movable parts, which, for example, could be subject to accelerations when used in vehicles, the laser scanner according to the invention is less sensitive to vibrations and shock loads and can therefore be used without problems in mechanically movable objects such as vehicles, in particular industrial transport vehicles. Since the laser scanner has no movable parts, the laser scanner can also be implemented very compactly.

[0062] In a further development of the invention, the laser scanner has at least one transmitting element and at least one receiving element and a control and evaluation unit for evaluating the light flight time of the light beam from the transmitting element via the object to the receiving element. In this case, a deflection unit is provided for deflecting the transmitting light beam of the transmitting element and / or for deflecting the receiving light beam of the receiving element. For example, the deflection element can be a rotating mirror or an oscillating mirror.

[0063] By means of the deflection unit, only a single transmitting element and / or a single receiving element need to be provided.

[0064] In an extended solution of the present invention, the laser scanner is a multi-plane laser scanner, wherein the multi-plane laser scanner is designed to form a plurality of scanning planes. For example, the plurality of scanning planes can be arranged in a fan shape. However, a plurality of parallel scanning planes can also be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Other advantages and features of the present invention will be described below based on embodiments with reference to the accompanying drawings. In the accompanying drawings:

[0066] Figure 1 A high-side driver solution according to the prior art is shown;

[0067] Figure 2 A resonant capacitor discharge laser driver according to the prior art is shown;

[0068] Figure 3 An improved low-side driver design based on a single transistor avalanche pulse design according to the prior art is shown;

[0069] Figure 4 A resonant laser driver with a high-side boost circuit according to the prior art is shown;

[0070] Figure 5 An electronic circuit for generating laser pulses for a laser scanner is shown;

[0071] Figure 5a An electronic circuit for generating laser pulses for a laser scanner is shown;

[0072] Figure 6 An electronic circuit for generating laser pulses for a laser scanner is shown;

[0073] Figure 6a An electronic circuit for generating laser pulses for a laser scanner is shown;

[0074] Figure 6b An electronic circuit for generating laser pulses for a laser scanner is shown;

[0075] Figure 7shows the signals that occur as well as graphs of voltage and current;

[0076] Figure 8 A laser scanner is shown.

[0077] In the following figures, identical parts are provided with the same reference symbols.

[0078] Figure 5 An electronic circuit 1 for generating laser pulses for a laser scanner is shown, the electronic circuit 1 comprising: an input contact 3 for an input voltage; a series circuit connected to the input contact, the series circuit comprising at least one coil L1 and at least one first diode D1, wherein the first diode D1 is connected in the forward conduction direction of the input voltage, wherein at least one switching element Q1 connected to the series circuit is arranged, wherein a switching path is formed by means of the switching element Q1, wherein a laser trigger signal 12 can be applied to the gate of the switching element Q1, wherein at least one anti-parallel circuit including a laser diode LD and a second diode D2 is connected to the cathode of the first diode D1 and the switching element Q1 at one end, wherein the anti-parallel circuit of the laser diode LD and the second diode D2 is connected to at least one first capacitor C1 at the other end, and the first capacitor C1 is grounded at the other end, wherein an optical laser pulse can be generated at the laser diode LD by the laser trigger signal 12 at the switching element Q1.

[0079] Figure 5 An electronic circuit 1 is shown, which includes an input contact 3 for an input voltage, and at least includes a coil L1 connected to the input contact and a first diode D1 connected in series with the coil L1, wherein the first diode D1 is connected in a forward conduction direction of the input voltage, wherein at least a switching element Q1 connected to the cathode of the first diode D1 is arranged.

[0080] However, according to Figure 5a , the diode D1 may also be connected to the input contact, and the coil L1 may be connected in series with the diode D1, so that the coil L1 and the diode D1 form a series circuit.

[0081] For example, according to Figure 6 , at least one second capacitor C2 connected in parallel to the input contact 3 is arranged.

[0082] After startup and applying voltage at input contact 3, the input voltage at input contact 3 charges the second capacitor C2 and the first capacitor C1 via coil L1, first diode D1 and second diode D2. The first capacitor C1 is a single capacitor or a series of capacitors to buffer the energy required for a single laser shot. The second capacitor C2 is a capacitor or, for example, a plurality of large-capacity capacitors having a much larger capacitance than the first capacitor C1.

[0083] For example, the switching element Q1 is a switching element Q1 with a very fast switching time, which can carry a high peak current and withstand a high charging voltage during a laser pulse. The switching element Q1 is controlled by an external laser trigger signal 12 or a control signal at the control signal input terminal 4. Preferably, a low-side driver is provided to drive the gate of the switching element Q1 used. When the external laser trigger signal 12 is activated at a positive level, the switching element Q1 is turned on only for a very limited time.

[0084] Figure 6a An electronic circuit 1 is shown, which includes an input contact 3 for an input voltage, and at least includes a coil L1 connected to the input contact and a first diode D1 connected in series with the coil L1, wherein the first diode D1 is connected in a forward conduction direction of the input voltage, wherein at least a switching element Q1 connected to the cathode of the first diode D1 is arranged.

[0085] However, according to Figure 6b , the diode D1 may also be connected to the input contact 3, and the coil L1 may be connected in series with the diode D1, so that the coil L1 and the diode D1 form a series circuit.

[0086] according to Figure 6a and Figure 6b , the other laser diodes LD are arranged in parallel. The laser diodes LD have anti-parallel diodes D2, D3 or Dn. The capacitors C2, C3 or Cn are connected in series with the corresponding laser diodes LD, and the other ends are grounded.

[0087] Figure 7 The occurring signals are shown as well as diagrams of voltage and current. Figure 7 The diagram shows the signal of the laser trigger signal 12, the current through the coil L1, the voltage at the first capacitor C1 and the light signal at the laser diode LD. In particular, the relevant time points t1, t2, t3 and t4 are shown. VIN represents the input voltage. Imax represents the maximum current through the coil L1.

[0088] During the first pulse of the laser trigger signal 12, according to Figure 7 Starting from the first time point t1, the first capacitor C1 is completely discharged through the laser diode LD and the switching element Q1, and the first lower laser pulse is generated. At this time, the voltage level of the cathode of the laser diode (corresponding to the drain terminal of the switching element Q1) is the same as the ground reference, which causes the voltage drop from the second capacitor C2 to the switching element Q1 to be equal to the input voltage. Current begins to flow through the coil L1 and the first diode D1.

[0089] After the switching element Q1 is closed, the current through the coil L1 and the first diode D1 continues to increase and charges the first capacitor C1 to the voltage of the second diode D2 until the voltage level at the cathode of the laser diode reaches the magnitude of the input voltage at the second time point t2 and is now at the same voltage level as the second capacitor C2. From now on, the current through the coil L1 decreases until it reaches 0 amperes again at the third time point t3. During this period, the first capacitor C1 is still charged to a voltage level that is almost twice the input voltage.

[0090] After the third time point t3, the first diode D1 prevents negative current from flowing through the coil L1, so that the first capacitor C1 does not discharge through the laser diode LD and the coil L1. Under real conditions, only slight oscillations remain, but this does not lead to undesired illumination of the laser diode LD. The first capacitor C1 stores energy for the next laser pulse with a charging voltage that is almost twice the input voltage until the laser trigger signal 12 triggers the circuit again at the fourth time point t4.

[0091] The switching element Q1 is closed only for a limited time, in particular an extremely limited time, namely a few nanoseconds, to release the laser pulse. During this time, no significant current can be established through the coil L1 and the switching element Q1. However, the very short time that the switching element Q1 is closed is sufficient to bring the voltage level at the cathode of the laser diode close to 0 volts and to start the above-mentioned charging current. As long as the switching element Q1 is not closed for a long time, the voltage at the first capacitor C1 after charging is almost twice the input voltage, regardless of when the switching element Q1 is closed. On the one hand, this means that the possibility of directly controlling the charging voltage is lost with the closing time of the switching element Q1. On the other hand, it is impossible to generate a voltage higher than twice the input voltage, so the maximum energy of each pulse is completely predictable. No additional safety mechanisms, such as high-speed voltage measurement, are required. And the energy of each pulse can still be controlled by varying the input supply voltage, which can be measured by a relatively slow voltage measurement.

[0092] To further increase the sensitivity to an erroneous pulse width of the laser trigger signal 12, a coil L1 or an inductor can be used, wherein the peak charging current through the coil L1 is close to the saturation current of the inductor type. Even if the pulse width of the laser trigger signal 12 is too large, the coil L1 or the inductor cannot store more magnetic energy, thereby preventing overloading of the first capacitor C1. In addition, the current through the coil L1 rises quickly, and an easily implemented power switch can identify this fault condition.

[0093] The laser diode LD is, for example, a 5J VCSEL laser diode or a multi-channel edge emitter.

[0094] Preferably, the switching element Q1 is in particular a switching transistor, in particular a field effect transistor FET-Q1 , very particularly a gallium nitride field effect transistor GaN-Q1 .

[0095] Preferably, the laser trigger signal 12 is generated by a low-side FET driver. The low-side FET driver is an integrated electronic circuit that drives a power switch, ie, the switching element Q1.

[0096] A transistor driver or low-side FET driver is a circuit that provides the necessary voltage to switch the switching element Q1 on or off within the required time. Here, it is usually an amplifier with an additional level shifter. This allows large loads, such as a field effect transistor FET-Q1, to be switched with a logic output that is usually operated at 5V or 3.3V. The driver can operate in analog or digital mode.

[0097] During the first pulse of the laser trigger signal 12, starting from the first time point t1, the first capacitor C1 is completely discharged through the laser diode LD and the switching element Q1, and a first lower laser pulse is generated. At this time, the voltage level of the cathode of the laser diode is the same as the ground reference, which causes the voltage drop from the second capacitor C2 to the switching element Q1 to be equal to the input voltage. If the pulse width of the laser trigger signal 12 is selected to be longer than the calculated laser pulse width, the complete discharge of the first capacitor C1 is ensured.

[0098] Preferably, the capacitance of the second capacitor C2 is at least 500 times greater, in particular 1000 times greater, than the capacitance of the first capacitor C1 .

[0099] Preferably, the switching element Q1 is closed by the laser trigger signal 12 for only 5 nanoseconds to 30 nanoseconds, in particular for only 15 nanoseconds to 20 nanoseconds, in order to release the laser pulse at the laser diode LD.

[0100] An extended concept relates to a driver circuit for a laser diode LD in pulsed laser applications in which the pulse width is a few nanoseconds, in particular 5 ns to 20 ns, and the pulse energy is high, for example a few microjoules per laser shot, and high peak currents, for example currents of more than 100 amperes, are used.

[0101] Preferably, the energy of each laser pulse is set by controlling the input supply voltage.

[0102] The energy of each laser pulse can therefore be set or controlled or regulated simply by means of the input supply voltage used.

[0103] Preferably, the first capacitor C1, the laser diode LD and the switching element Q1 form a resonant discharge laser driver.

[0104] However, unlike conventional solutions, the charging circuit is connected to the cathode side of the laser driver, while the capacitor remains connected to the anode. To enable current flow for charging, an anti-parallel second diode D2 is added. With this change, the critical failure of the short-circuited switching element is overcome.

[0105] Preferably, the coil L1 , the first diode D1 and the switching element Q1 preferably form a boost converter circuit.

[0106] In order to overcome the relatively low efficiency of 50% of the commonly used charging resistor, a circuit with a common boost converter topology is used, which includes a coil L1, a first diode D1 and a switching element Q1. A high-speed switching element of an oscillating drive loop is used, wherein the high-speed switching element is closed only for a limited time, in particular a very limited time, so that due to the circuit, a voltage that depends only on the input voltage and is therefore deterministic is generated, which voltage is almost equivalent to twice the input voltage.

[0107] Exemplary specific values ​​for the components are as follows:

[0108] C2=2×4.7uF(~10uF)

[0109] L1=6.8μH

[0110] D1 = NEXPERIA PMEG3010 (low VF Schottky diode)

[0111] Q1=EPC EPC2088 (GaN enhancement mode power transistor)

[0112] D2 = NEXPERIA PMEG3010 (low VF Schottky diode)

[0113] LD (Laser Diode) = AMS TORONTO (800W 940nm 5J-VCSEL)

[0114] C1=3×3.9nF ceramic capacitor (11.7nF)

[0115] Input voltage = 25-35V

[0116] Gate driver = TI LMG1020

[0117] Figure 8A laser scanner 2 is shown with an electronic circuit 1. The laser scanner 2 has at least one transmitting element 5 and at least one receiving element 6 and a control and evaluation unit 7 for evaluating the light flight time of a light beam from the transmitting element 5 via an object 8 to the receiving element 6. The transmitting element has a laser diode LD. An optional lens 13 is arranged in front of the transmitting element 5 and the receiving element 6. For the sake of clarity, not all signal connections to the electronic circuit 1 are shown.

[0118] according to Figure 8 , a plurality of transmitting elements 5 and a plurality of receiving elements 6 are arranged in a common housing 9, wherein the light beam 11 is emitted and / or received in a fan-shaped manner in different angular directions, wherein the distance of the emitted light beam of the transmitting element 5 increases as the distance to the laser scanner 2 increases, and / or the distance of the received light beam of the receiving element 6 decreases as the distance to the laser scanner 2 decreases. For example, the transmitting elements and the receiving elements are arranged in a row. The angular deflection can be achieved by an optical device. However, the transmitting elements and the receiving elements can also be arranged in the shape of a circular segment.

[0119] A preferred application is the use of the electronic circuit in a laser class 1 lidar sensor.

[0120] According to the extended solution, the light beam 11 is emitted or received in a fan shape in different angular directions, thereby making it easy to check the monitoring area and determine whether there is an object 8 in the monitoring area and at which position, that is, the distance at which the object is located. In addition, the object 8 can be measured, or the surrounding contour and its changes can be detected. The monitoring area is monitored in a fan-shaped plane by fan-shaped emission or fan-shaped reception of the light beam. For example, the transmitting element 5 or the receiving element 6 is arranged radially symmetrically on the circumference of a cylinder. The laser scanner 2 can be manufactured with high angular accuracy because the transmitting element 5 and the receiving element 6 are firmly fixed and the light beam 11 reaches the monitoring area directly without moving parts. During the production process of the laser scanner, the angular accuracy of the angular direction can be checked and set. Thereby, it is ensured that each laser scanner complies with the specific required minimum angular accuracy.

[0121] For example, in an alternative embodiment, the laser scanner 2 has at least one transmitting element 5 and at least one receiving element 6 and a control and evaluation unit 7 for evaluating the light flight time of the light beam 11 from the transmitting element 5 via the object 8 to the receiving element 6. In this case, a deflection unit is provided for deflecting the transmitting light beam of the transmitting element 5 and / or for deflecting the receiving light beam of the receiving element 6. The transmitting element has a laser diode LD.

[0122] The deflection unit only needs to provide a single transmitting element 5 and / or a single receiving element 6 .

[0123] For example, the laser scanner is a multi-plane laser scanner, wherein the multi-plane laser scanner is designed to form a plurality of scanning planes. For example, the plurality of scanning planes can be arranged in a fan shape. However, a plurality of parallel scanning planes can also be formed.

[0124] Reference Mark List

[0125] 1 Electronic Circuit

[0126] 2 Laser Scanner

[0127] 3 input contacts

[0128] 4 Control signal input terminal

[0129] 5 Transmitter

[0130] 6 Receiving element

[0131] 7 Control and evaluation unit

[0132] 8 Objects

[0133] 9 Housing

[0134] 11 Beam

[0135] 12 Laser trigger signal

[0136] 13 Lens

[0137] C1 First capacitor

[0138] L1 Coil

[0139] D1 First diode

[0140] Q1 Switching element

[0141] LD Laser Diode

[0142] D2 Second diode

[0143] C2 Second capacitor

[0144] FET-Q1 Field Effect Transistor

[0145] GaN-Q1 gallium nitride field effect transistor.

Claims

1. An electronic circuit (1) for generating laser pulses for a laser scanner (2), comprising: Input contacts for input voltage (3), A series circuit connected to the input contact (3), the series circuit comprising at least one coil (L1) and at least one first diode (D1), wherein the first diode (D1) is connected in a forward conduction direction of the input voltage, It is characterized in that At least one switching element (Q1) is arranged to be connected to the series circuit, wherein a switching path is formed by means of the switching element (Q1), The laser trigger signal (12) can be applied to the gate of the switching element (Q1). wherein at least one anti-parallel circuit including a laser diode (LD) and a second diode (D2) is connected at one end to the cathode of the first diode (D1) and the switching element (Q1), wherein the anti-parallel circuit of the laser diode (LD) and the second diode (D2) is connected to at least one first capacitor (C1) at the other end, And the first capacitor (C1) is grounded at the other end, The laser trigger signal (12) at the switching element (Q1) can generate an optical laser pulse at the laser diode (LD).

2. The electronic circuit (1) according to claim 1, characterized in that At least one second capacitor (C2) connected in parallel to the input contact (3) is arranged.

3. The electronic circuit (1) according to claim 1, characterized in that The switching element (Q1) is a switching transistor, in particular a field effect transistor (FET-Q1), in particular a gallium nitride field effect transistor (GaN-Q1).

4. The electronic circuit (1) according to any one of the preceding claims, characterized in that The laser trigger signal (12) is generated by a low-side driver.

5. The electronic circuit (1) according to claim 2, characterized in that The capacitance of the second capacitor (C2) is at least 500 times greater, in particular 1000 times greater, than the capacitance of the first capacitor (C1).

6. The electronic circuit (1) according to any one of the preceding claims, characterized in that The switching element (Q1) is closed by the laser trigger signal (12) for only 5 nanoseconds to 50 nanoseconds, in particular 15 nanoseconds to 20 nanoseconds, to release a laser pulse at the laser diode (LD).

7. The electronic circuit (1) according to any one of the preceding claims, characterized in that The energy of each laser pulse is set by controlling the input supply voltage.

8. The electronic circuit (1) according to any one of the preceding claims, characterized in that The energy of each laser pulse is not set by changing the pulse width of the laser trigger signal (12).

9. The electronic circuit (1) according to any one of the preceding claims, characterized in that The first capacitor (C1), the laser diode (LD) and the switching element (Q1) form a resonant discharge laser driver.

10. The electronic circuit (1) according to any one of the preceding claims, characterized in that The inductor (L1), the first diode (D1) and the switching element (Q1) form a boost converter circuit, wherein the switching element (Q1) is closed only for a limited time, so that due to the circuit a voltage is generated which depends only on the input voltage and is therefore deterministic and corresponds to almost twice the input voltage.

11. The electronic circuit (1) according to any one of the preceding claims, characterized in that The anti-parallel circuit of the laser diode (LD) and the second diode (D2) is connected in parallel with a further anti-parallel circuit of a laser diode (LD) and a diode, wherein these anti-parallel circuits are each connected to at least one further capacitor and the capacitor is grounded at the other end, wherein the laser trigger signal at the switching element (Q1) can generate optical laser pulses simultaneously at all laser diodes (LD).

12. The electronic circuit (1) according to claim 9, characterized in that The laser diodes (LD) are arranged in a common housing (9) or on a common substrate.

13. A laser scanner (2) comprising at least one transmitting element (5) and at least one receiving element (6) and a control and evaluation unit (7), wherein the control and evaluation unit (7) is used to evaluate the light flight time of a light beam from the transmitting element (5) via an object (8) to the receiving element (6), the laser scanner (2) comprising an electronic circuit (1) according to any one of claims 1 to 12.

14. The laser scanner (2) according to claim 13, characterized in that A plurality of transmitting elements (5) and a plurality of receiving elements (6) are arranged in a common housing (9), wherein the light beam (11) is emitted and / or received in a fan-shaped manner in different angular directions, wherein the distance of the emitted light beam (11) of the transmitting element (5) increases as the distance to the laser scanner (2) increases, and / or the distance of the received light beam (11) of the receiving element (6) decreases as the distance to the laser scanner (2) decreases.

15. The laser scanner (2) according to claim 13, characterized in that A deflection unit is provided for deflecting a transmission light beam of the transmitting element (5) and / or for deflecting a reception light beam of the receiving element (6).

16. The laser scanner (2) according to claim 13, characterized in that The laser scanner (2) is a multi-plane laser scanner, wherein the multi-plane laser scanner is designed to form a plurality of scanning planes.

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