Fast-Pulse, High-Current Laser Driver

Abstract

Disclosed is a pulsed laser driver including gallium nitride (GaN) power transistors for driving diode laser systems requiring high current and fast pulses, such as laser drivers for LIDAR (Light Detection and Ranging) systems. The driver is capable of delivering pulses with peak current ≥100A (e.g., 170A) to provide high peak power, fast pulses with nanosecond rise time and nanosecond pulse duration for driving a multi-channel laser diode array with 40A per channel, 120W output per channel, and a combined peak output of 480W. For lower duty cycles, an example driver circuit is disclosed that includes high current power transistors for direct drive with driver assistance. For higher duty cycles, an example resonant driver circuit is disclosed that includes two high current power transistors. Implementation of the resonant driver circuit using GaN technology provides fast charging for short pulse operation at higher repetition rates or for pulse code modulation.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 281,484, filed on March 1, 2019, entitled “FAST PULSE, HIGH CURRENT LASER DRIVERS,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to pulsed laser drivers, and in particular to driver circuits incorporating gallium nitride (GaN) power transistors for driving diode laser systems requiring high current and fast pulses, such as laser drivers for LIDAR (Light Detection and Ranging) systems. Background Art

[0004] LIDAR systems use light pulses to measure the distance to an object based on time of flight (ToF). Distance is calculated based on the time that passes between the emission of a light pulse from a light source (emitter), such as a laser diode, and the detection of the reflected pulse of light by a detector mounted near the emitter. Some systems use a single light emitter and detector with a rotating mirror to scan across a plane (two-dimensional / 2D systems). Three-dimensional (3D) LIDAR systems scan in two planes, horizontal and vertical. Other 3D systems use arrays of multiple light emitters and detectors.

[0005] For background information on LIDAR for automotive applications such as autonomous driving, reference is made to a presentation entitled “LIDAR Teach-In” presented by OSRAM Licht on June 20, 2018.

[0006] For long-range applications such as collision avoidance for moving vehicles and for accurate identification of stationary and moving objects at long distances, LIDAR time-of-flight systems require high-power, fast optical pulses, such as nanosecond pulse widths with peak powers exceeding 100W.

[0007] Recently, it has been recognized that wide-bandgap semiconductor devices based on silicon carbide (SiC) technology and gallium nitride (GaN) technology offer advantages over silicon power MOSFETs for fast, high-current switching of this type of laser driver circuit. For example, GaN power transistors are now commercially available that provide very fast, nanosecond-timescale switching for currents in the tens to hundreds of amperes range, operating at voltages in the 100V to 650V range.

[0008] For example, US2018 / 0323576A1, entitled “Pulsed Laser Diode Driver and Method,” published by Crawford et al. (Analog Modules) on November 8, 2018, discloses a current driver for generating very short pulses at high current for a high-power laser diode using a current control device comprising a GaN FET or SiC FET in series with the laser diode; US2018 / 0284227A1, entitled “Integrated LIDAR Illumination Power Control,” published by Hall et al. (Velodyne Lidar) on October 4, 2018, discloses a method and system comprising a GaN-based illumination driver integrated circuit; and US2018 / 0284227A1, entitled “Integrated LIDAR Illumination Power Control,” published by Pavlov et al. (SensL Technologies) on September 13, 2018, discloses a method and system comprising a GaN-based illumination driver integrated circuit. US 2018 / 0261975A1, titled "Laser Driver", discloses a laser driver comprising a resonant circuit with an inductor and a DC blocking capacitor and using a GaN transistor driven by a MOSFET gate.

[0009] While these references provide some examples of the advantages of GaN power switching devices for fast pulsed laser drivers, there is a need for further improvements in pulsed laser driver circuits for laser diodes that can deliver higher currents and faster pulse widths. For example, for LIDAR systems, there is a demand for diode lasers and diode laser arrays that require very high currents (>100A) and short pulses with nanosecond rise times and pulse widths (pulse durations) with nanosecond FWHM (full width at half maximum). Conventional Si MOSFET-based laser driver circuits cannot deliver the required performance, for example, due to one or more of slow transistors, low current drivers, high inductance layouts, and poor topology selection.

[0010] To fully exploit the capabilities of GaN power transistors as fast, high current switching devices for laser drivers, improved pulsed laser driver circuits are needed to overcome one or more of these limitations.

[0011] Therefore, there is a need to develop improved or alternative driver solutions for driving pulsed laser diodes and pulsed laser diode arrays for applications such as LIDAR. Summary of the Invention

[0012] The present invention seeks to provide a pulsed laser driver for driving diode laser systems requiring fast, high current switching, such as laser drivers for LIDAR systems, which alleviates or circumvents one or more limitations of known solutions, or at least provides an alternative.

[0013] For lower duty cycle applications, a pulsed laser driver is provided that includes a current switch for direct drive with driver assistance, wherein the current switch includes a fast, high-current GaN power transistor, Qmain, driven by a gate drive assist circuit comprising a single, low-current transistor, Qdriver, and a resistor arrangement. A fast pulsed gate drive signal turns Qdriver on / off to provide rapid on / off switching of Qmain to excite the laser, thereby generating laser pulses with nanosecond rise times and pulse durations and high peak power.

[0014] One aspect of the present invention provides a pulsed laser driver for directly driving a laser diode or a laser diode array, comprising:

[0015] a current switching device comprising an e-type high current GaN power transistor (Qmain) having a source, a drain, and a gate;

[0016] A driver auxiliary circuit, which includes a low current e-type transistor (Qdriver) and a driver resistor R1,

[0017] The drain of Qdriver is connected to the first power terminal V+ through R1 and the source of Qdriver is connected to the second power terminal V0, and the driver circuit has a gate drive input connected to the gate of Qdriver for receiving a gate drive signal;

[0018] The high side of R1 is connected to the gate of Qmain and the low side of R1 is connected to the source of Qmain.

[0019] Another aspect of the present invention provides a pulsed laser driver for directly driving a laser diode or a laser diode array, comprising:

[0020] a current switching device comprising an e-type high current GaN power transistor (Qmain) having a source, a drain, and a gate;

[0021] A driver auxiliary circuit, which includes a low current D-type transistor (Qdriver) and a driver resistor R1,

[0022] the drain of Qdriver is connected to the first power terminal V+ through R1 and the source of Qdriver is connected to the second power terminal V−, and the driver circuit has a gate drive input connected to the gate of Qdriver for receiving a gate drive signal;

[0023] The low side of R1 is connected to the gate of Qmain, and the source of Qmain is coupled to the third power terminal V0.

[0024] The laser driver may comprise discrete components, or in a module integrating these components, for example as one or more functional blocks.

[0025] For example, for a pulsed laser driver for direct driving with driver assistance ("direct drive laser driver"), where Qdriver is a GaN transistor, it can be integrated with Qmain. Where Qdriver is a Si MOSFET or SiC transistor, it can be co-packaged with Qmain.

[0026] Other aspects of the present invention provide: a module comprising a direct drive laser driver connected in series with a laser diode or laser diode array D3 for directly driving D3; a LIDAR device comprising a direct drive laser circuit; and a LIDAR device comprising a module integrating a direct drive laser driver circuit and a diode laser array.

[0027] For example, in an exemplary embodiment, the laser driver is configured to generate current pulses having a nanosecond rise time and pulse duration and a peak current ≥ 100 V (e.g., a peak current of 170 A) for driving a multi-channel laser diode array, such as a four-laser array, driven at 40 A per channel, to produce 120 W peak power per channel or a total of 480 W peak power output from the laser. Pulsed laser drivers for direct drive with driver assistance are suitable for low duty cycle applications.

[0028] For higher duty cycle applications, faster charging / recharging is required, and a pulsed laser driver including a resonant drive is disclosed, which includes two fast, high current GaN power transistors Q1 and Q2, that is, as high-side and low-side current switches in the resonant circuit loop. Q1 and Q2 are turned on to initiate the charging or recharging operation to establish the current, and when the resonant current reaches the desired value, the rapid disconnection of Q2 provides a fast, high current pulse to trigger the laser pulse. The resonant driver provides fast high current switching, with faster (re)charging for higher repetition rates (e.g., defined for longer range LIDAR), and enables applications such as LIDAR with pulse code modulation.

[0029] Therefore, another aspect of the present invention provides a pulsed laser driver for resonant driving of a laser diode or a laser diode array D3, comprising:

[0030] first and second switching devices comprising high current GaN power transistors Q1 and Q2, each having a source, a drain, and a gate;

[0031] Q1 and Q2 are part of a resonant driver circuit including a resonant inductor L1 and a resonant DC capacitor C1, wherein the drain of Q1 is connected to the first power terminal V+, the source of Q1 is connected to the drain of Q2 through L1, the source of Q2 is connected to the second power terminal V0, and C1 is connected between the first and second power terminals V+, V0 to form a resonant tank.

[0032] a first terminal for connection to an anode A of said laser diode or diode array D3 and a second terminal for connection to a cathode K of said laser diode or diode array D3;

[0033] The first terminal is connected to a node between the low side of L1 and the drain of Q2 through a DC blocking diode D1 , and the second terminal is connected to the source of Q2 to form a laser power loop, and the laser power loop includes a series resonant capacitor C3 .

[0034] Since Q2 is only turned off to trigger the laser pulse, Q2 can be a normally-on GaN transistor. After triggering, the laser pulse Q1 can be held for a period of time, allowing the energy from L1 to C1 to recover or recover. During this recovery period, L1 acts as a current source. DC blocking diode D1 and diode D2, placed in antiparallel with laser diode / diode array D3, limit the reverse voltage to protect D3. D1 helps recover energy in the system (C3 energy). The circuit can include an energy recovery circuit connecting C3 to C1.

[0035] A pulsed laser driver for resonant drive may comprise discrete components, or in a module integrating these components, for example as one or more functional blocks.

[0036] Other aspects of the present invention provide: a module comprising a pulsed laser driver for resonant drive integrated with a laser diode or laser diode array D3 for directly driving D3; a LIDAR device comprising a laser driver circuit for resonant drive; and a LIDAR device comprising a module integrating a laser driver circuit for resonant drive with a diode laser / diode laser array.

[0037] For example, in an exemplary embodiment, the laser driver is configured to generate current pulses having a nanosecond rise time and pulse duration and a peak current of 170 A. For example, in a module containing a multi-channel laser array (e.g., a four-diode laser array), the driver is configured to generate current pulses having a nanosecond rise time and pulse duration with a peak current of 170 A to drive each channel at 40 A to provide an output of 120 W per channel, for a peak power of 480 W.

[0038] A method of operating a pulsed laser driver for resonant drive, as described herein, is also provided. The method may include generating a single laser pulse per cycle. The method may include generating multiple pulses per cycle, for example to achieve pulse encoding.

[0039] Thus, exemplary embodiments of laser drivers are disclosed that utilize the properties of GaN power transistors as fast, high-current switches to drive laser diodes and laser diode arrays requiring >100V current for generating laser pulses, e.g., with nanosecond rise times and FWHM in the sub-nanosecond to tens of nanosecond ranges. In exemplary embodiments, GaN power transistors can be used to implement pulsed laser drivers including direct drive with driver assistance and pulsed laser drivers including resonant drive circuits. In other embodiments, SiC power transistors, or Si power MOSFETs, or a combination of GaN power transistors and SiC or Si power MOSFETs can be used to implement pulsed laser drivers.

[0040] Thus, embodiments of the present invention provide laser driver circuits for driving high current, fast pulsed laser diodes and diode arrays for fast pulsed, high power laser systems, such as LIDAR systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 shows a simplified schematic diagram of a LIDAR system;

[0042] Figure 2 A schematic diagram of a circuit including a four-diode laser array and a laser driver including GaN transistor switches and a driver circuit for "direct drive with driver assistance" is shown;

[0043] FIG3A (Prior Art) shows a circuit schematic of a laser driver including a GaN transistor switch with a first conventional driver circuit;

[0044] FIG3B (Prior Art) shows a circuit schematic of a laser driver including a GaN transistor switch with a second conventional driver circuit;

[0045] Figure 4A A circuit schematic diagram of a laser driver including a GaN transistor switch and a driver circuit according to a first embodiment is shown;

[0046] Figure 4B A circuit schematic diagram of a laser driver including a GaN transistor switch and a driver circuit according to a second embodiment is shown;

[0047] Figure 5 a circuit schematic showing, in greater detail, an implementation of a GaN transistor switch and driver circuit of the first embodiment, suitable for low duty cycles;

[0048] Figure 6 a circuit schematic illustrating an implementation of a second embodiment of a GaN transistor switch and driver circuit, suitable for higher duty cycles, is shown in greater detail;

[0049] Figure 7 A circuit schematic diagram of a laser driver including a resonant driver circuit of an embodiment is shown, the resonant driver circuit including first and second (high-side and low-side) GaN transistor switches;

[0050] Figure 8A and Figure 8B shows a circuit schematic, Figure 8C shows an example of a graph of the resonant circuit current and the laser current as a function of time for one pulse;

[0051] Figure 9 Shown in more detail Figure 7 A circuit diagram of an implementation of a resonant driver circuit; and

[0052] Figure 10 shows the method for driving a four-pulse laser diode array. Figure 9 A set of waveforms A to G of the operation of the resonant driver circuit.

[0053] The above and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings of preferred embodiments of the present invention, which description is by way of example only. DETAILED DESCRIPTION

[0054] Figure 1 Shown is a simplified schematic diagram of a LIDAR system 1. Descriptions of the components and operating principles of this type of LIDAR system can be found, for example, in the patent and non-patent references mentioned above.

[0055] In summary, the range R is determined from the transit time Δt and the speed of light c as: R = c·Δt / 2 and δR = c / 2B.

[0056] Higher power lasers have longer ranges, and shorter laser pulse widths provide better resolution. Even better clarity is achieved with higher frequency pulses, i.e., higher pulse repetition rates, which can range from kHz to MHz.

[0057] LIDAR systems for automotive applications such as collision avoidance systems are typically based on diode lasers operating at <1000 nm (e.g., 905 nm). Laser diodes operating at >1000 nm, such as 1555 nm, are under development and may be preferred for eye safety, but these are not currently economically viable.

[0058] Pulsed laser driving circuit using driver assistance for direct drive

[0059] Figure 2 A circuit schematic of a system 10 is shown, including a four-diode laser array 12 and a laser driver circuit 20 according to a first embodiment. The laser diode array 12 comprises four parallel laser diodes connected in series with a current switching device comprising a fast, high-current GaN power transistor 22 controlled by a driver assist circuit 24. Power is supplied to the laser array via a high-current power supply 14 and a charging capacitor 16. For each pulse, when the GaN power transistor 22 is off, the charging capacitor 16 is charged from the high-current power supply 14 through a resistor 26. For example, the charging voltage can be 200V, or any suitable value, typically in the range of 10V to 400V. To excite the laser array, a pulsed control signal is provided to the input of the driver assist circuit 24, switching the high-current GaN transistor 22 on and off for a period of time that controls the pulse duration, causing current to flow through the laser diode array to generate light pulses.

[0060] For example, for long-range LIDAR applications, an array of four laser diodes is used, and the optical requirements include, for example:

[0061] For long distances, the peak optical power is 480W, or 120W per channel;

[0062] Driving the four-laser array requires 160A of current, or 40A per laser diode;

[0063] 1ns pulse duration / response for object discrimination, thermal performance, and eye safety; with a duty cycle / pulse repetition rate of <1,000ns between laser shots.

[0064] Additionally, pulse encoding using a series of multiple pulses in each 1000 nanosecond period may be required to create a unique signature for each LIDAR device.

[0065] To meet these optical requirements, the electrical requirements for driving the laser diode array include a main GaN transistor switch 22 capable of fast switching (nanosecond timescale) of currents greater than 100A, and low inductance circuitry is required to achieve nanosecond switching. High frequency operation, i.e., with high pulse repetition rates, also requires fast transistors with large currents and high CTMI transistor drivers. Pulse encoding requires fast recharge. GaN power transistors offer higher current density and therefore higher currents and lower power losses than silicon power MOSFETs. Therefore, replacing Si MOSFETs with GaN FET current switches 22 offers significant advantages for high current, fast switching. In order to benefit from the advantages of GaN FETS for fast switching, fast driver circuits are also required.

[0066] Figures 3A and 3B show first and second conventional arrangements of Si MOSFET driver circuits, which include a pair (i.e., high-side and low-side) of driver SiMOSFETs D1 and D2 to drive the main transistor switch. Figure 3A shows an example using a single power supply, for example, for 0 to 6V operation. Figure 3B shows an example using a dual power supply, for example, for -6V to +6V operation. Each circuit requires first and second gate drive signals for D1 and D2, which creates timing issues for fast switching. This type of driver circuit with two driver auxiliary transistors is typically used for current switching applications requiring only 6A or 7A.

[0067] Figure 4A and 4B Driver circuits 20A and 20B of the first and second embodiments are shown, wherein the driver assist circuits 24A and 24B include a single fast switching, low current drive assist transistor Q driver To control the main GaN FET power switch 22 (Q main ) on and off. Figure 4A An embodiment is shown using a single power supply V+, for example for 0 to 6V operation. Figure 4B Embodiments using dual power supplies, V+ and V-, for example, -6V to +6V operation are shown. In these embodiments, a resistor replaces the conventional second driver auxiliary transistor to provide a simpler, faster switch driver. Because only one driver auxiliary transistor, Qdriver, is present, the circuit requires only one gate drive signal, eliminating the timing issues associated with the gate drive signals for driver transistors D1 and D2 in the conventional driver circuits of Figures 3A and 3B.

[0068] refer to Figure 5 , which shows in more detail Figure 4AIn more detail of the implementation of the driver circuit 20A, the main current switch Qmain is a fast, high current GaN FET, such as GanSystem, GS66516T. The driver auxiliary transistor Qdriver is a fast, low current transistor, which can be a GaN FET, or a suitable SiC transistor or SiMOSFET with an anti-parallel diode. The circuit includes a driver resistor Rdriver (R1) and a capacitor C1. The circuit is suitable for the generation of short pulses with a small duty cycle. For a small duty cycle, Qdriver is off most of the time. When Q driver When Qdriver is turned off and the gate-source voltage Vgs of Qmain is zero, capacitor C1 is charged from the power supply V+. When Qdriver is turned on, that is, by receiving a control signal pulse to its gate, the voltage on capacitor C1, V+, is applied to Vgs through resistor Rdriver, turning on Qmain. This pre-driver circuit has only one transistor, Qdriver, to provide a simple, fast pulse driver with reduced timing issues, suitable for applications with low, short duty cycles.

[0069] refer to Figure 6 , which shows in more detail Figure 4B In more detail of the implementation of the driver circuit 20B, the main current switch Qmain is a fast, high current GaN FET, such as the GSGS66516T. The driver auxiliary transistor Qdriver is a fast, low current transistor, such as the GS66504B. There is a dual power supply, for example for -6V to +6V operation. Qdriver is normally on. During operation, when Qdriver is turned on, the gate-source voltage Vgs of Qmain is -6V, that is, V- is applied to the gate of Qmain and Qmain remains firmly off. When Qdriver receives a control pulse to its gate and is turned off, Vgs becomes +6V to turn on Qmain, that is, V+ is applied to the gate of Qmain to quickly turn on Qmain to excite the laser array. This pre-driver circuit has only one transistor Qdriver to provide a simple, fast pulse driver with reduced timing issues.

[0070] Figure 5 and Figure 6Both driver circuits use a fast, low-current driver auxiliary transistor, Qdriver, to turn the main transistor on and off to excite the laser array. Circuit 24A turns Qmain on very quickly. Circuit 24B turns Qmain off very quickly. These circuits are capable of providing fast, nanosecond on- and off-pulsing of Qmain to produce short laser pulses with nanosecond rise times and nanosecond full-width-high-mass (FWHM) for cycle times of 1000ns, or a kHz repetition rate, i.e., short pulses with a low duty cycle. Because power is dissipated in the driver circuit during the on-state of Qmain, this driver circuit arrangement is suitable for low-duty-cycle operation, in which the laser is off for most of the cycle.

[0071] Pulsed laser driver circuit with resonant drive

[0072] In a conventional laser diode driver circuit, turning on the driver transistor is used to inject current to activate lasing. Figure 7 An example of a four-laser array driven by a resonant driver using two GaN FETs, Q1 and Q2, and the LC components of the resonant driver circuit is shown. Figure 7 The LC components of the resonant drive circuit are not shown in FIG. In this laser driver, the switching off of Q2 is used to excite the laser array. That is, for operation, when both the high-side and low-side GaN transistors Q1 and Q2 are turned on, current flows from the power supply in the LC resonant driver circuit through Q1 and Q2. The high-side transistor Q1 is used to control the charging of the resonant circuit. When the resonant current through Q1 and Q2 reaches the required value, the rapid switching off of the low-side transistor Q2 directs a current pulse through the laser array to excite the lasers. For example, it has been demonstrated that this circuit is capable of achieving a current of 170A for simultaneously exciting a four-laser diode array, i.e., where each laser requires a peak power of 40A with a rise time of less than 1ns and a FWHM of 1.5ns. For example, Figure 8A and 8B The circuit diagram and Figure 8C The curve in shows the resonant current peaking at 170 A when both Q1 and Q2 are on, and the square laser diode current when the low-side transistor Q2 is off. This circuit eliminates the turn-on of the driver FET and instead uses fast turn-off for fast, high current switching.

[0073] Figure 9More details are shown for the implementation of a resonant drive circuit for driving a four-laser diode array D3 and including an embodiment of first and second (high-side and low-side) switching transistors Q1 and Q2. For fast switching at high currents, Q1 and Q2 are GaN FETs, such as the GS66516, with gate drivers Driver 1 and Driver 2, respectively. For faster shutdown, the driver circuit operates using both positive and negative power supplies V+ and V- (e.g., +6V and -6V). That is, applying a Vgs of, for example, -5V or -6V to Q2 ensures rapid and complete shutdown of the low-side driver transistor Q2, which directs the current pulses to excite the laser array. Compared to the direct drive circuit described herein, this resonant circuit driver can operate at a higher duty cycle because the driver transistor pair Q1 and Q2 work together to quickly charge, dissipate, and recover energy during the laser diode array shutdown period. In this example, Q1 and Q2 are e-mode (normally off) transistors. Because Q2's shutdown excites the laser, Q2 is turned on for most of the cycle, i.e., between pulses. Q2 can be a normally-on transistor (d-mode). Q1 is normally off, and its operation is used to start the operation of the resonant circuit and control the charging of the resonant circuit, which includes a resonant DC capacitor C1 and a resonant inductor L1. C1 and L1 resonate to establish a current in the loop. Then, when Q2 is turned off, the voltage at C1 is applied to direct a current pulse through the laser diode array D3 to generate a laser pulse. C2 is the parasitic capacitance of the driver transistor Q2; ideally, C2 is close to zero, but C2 can also be selected to adjust the parameters of the LC resonant circuit loop. C2 and L2 control the peak voltage of Q2. If the parasitic capacitance of Q2 is insufficient, for example if attenuation is required, C2 can be an additional capacitor. Also shown are the series resonant inductor L2 and the series resonant capacitor C3 in the laser current drive loop. L2 represents the inherent or parasitic inductance of the laser current drive loop. For faster switching, to reduce the inductance of the current drive loop, it is preferable to keep this path short, keeping L2 low. For example, a ~1nH series resonant capacitor C3 acts as a protective device and reduces the fall time of the pulse, i.e., making it sharper. D1 is an added series diode so that when C3 is charged, D1 blocks the reverse current path from the laser diode array, and the energy stored in C3 is sent back to the resonant capacitor C1 via the energy recovery circuit. An energy recovery circuit can be provided in parallel with C3 to send energy back to C1. During resonance, the energy in L1 is sent to C1. C3 makes the pulse sharper and stores energy that can be later recovered by the energy recovery circuit. D1 is a DC blocking diode, and an anti-parallel diode D2 is provided to limit the reverse voltage across the laser diode array D3 at the end of the pulse and during the recovery period. D1 and D2 work together to protect the laser diode array and reduce ringing.

[0074] The circuit parameters are selected, for example, so that when both Q1 and Q2 are on, the circuit resonates with a period of, for example, 20 ns to 100 ns. When the resonant current peaks, Q2 is turned off for the desired duration, for example, 4 ns, to generate a current pulse that excites the laser. When Q2 is turned on again, an energy recovery circuit, with L1 as the recovery current source, returns approximately 70% of the stored energy to C1. At the end of the cycle, Q1 is turned off. For example, the charging voltage is 200 V to provide the desired peak resonant current of 170 A. The circuit can be tunable, for example, in the range of 10 MHz to 50 MHz, for multiple resonances.

[0075] Figure 10 Shown for Figure 9 Some examples of typical waveforms of the operation of the circuit. Trace A shows the Vgs of Q1, which is turned on for 50ns for operation. Trace C shows the current I through the resonant inductor L1. L1 , while trace F shows the voltage V across the resonant capacitor C1 C1 Trace B shows the Vgs of Q2 as it is turned on to fire the laser for a period of, for example, 4ns. Trace G shows the voltage across C3 before and after laser ignition, including the energy recovery phase. Trace D shows the laser current.

[0076] like Figure 9 As shown in the schematic circuit diagram of FIG, the series capacitor C3 can be located at any suitable point in the laser power loop, such as Figure 10 As shown, rather than Figure 9 Alternatively, other series components can be positioned appropriately to provide the desired functions of the resonant ring and laser power ring. The energy recovery circuit element is connected to C3 to enable energy recovery of C1.

[0077] Thus, it was demonstrated that the resonant drive circuit provides fast switching to deliver high-power, fast laser pulses with nanosecond rise times and nanosecond full width at half maximum (FWHM). The drive circuit can control the number of pulses in each shot to enable pulse code modulation. A series diode protects the laser diode array from reverse voltage. There is no external inductance in the laser power loop, and the laser power loop layout is preferably configured for minimal inductance, such as short path length, low inductance interconnects, for faster switching and sharper (narrower FWHM) current pulses. The parasitic capacitance C2 of Q2 in the resonant circuit serves to limit the switching peak voltage. The resonant circuit and power loop are configured for fast recharging, including recovery of resonant energy stored in L1 and C3 after a laser pulse. Energy recovery also helps maintain a low operating temperature of the laser diode array because this excess energy does not need to be dumped or dissipated by the laser diodes after firing. Faster recharging also enables rapid firing of multiple pulses, for example, to increase discrimination of fast-moving targets. For situations where there may be interference from other nearby transmitters using the same wavelength, multiple pulses in one transmission can also be used in applications requiring pulse code modulation, i.e., generating a series or pattern of pulses that uniquely identifies a transmitter.

[0078] The system design provides for the GaN transistors Q1 and Q2 to be turned on and off under soft switching conditions (ie, under low power loss conditions) to reduce overall system losses and lower EMI (electromagnetic interference).

[0079] In the above embodiment of a resonantly driven laser driver, both Q1 and Q2 are fast, high-current GaN transistors. While it is important that the low-side transistor Q2 provide fast turn-off, such as nanosecond or sub-nanosecond, in other embodiments not shown, Q1 need not be a GaN transistor. For example, in alternative embodiments, Q2 is a GaN transistor and Q1 is a slower SiMOSFET or SiC transistor.

[0080] While the pulsed laser driver of the exemplary embodiment has been described in detail for nanosecond fast pulses, it should be understood that in alternative embodiments, circuit parameters can be selected to provide a pulsed laser driver for pulse widths in the sub-nanosecond to tens of nanosecond ranges at high peak currents (e.g., ≥100 A). For lower power laser diode arrays, a pulsed laser driver providing embodiments of tens of amperes is sufficient to provide, for example, peak powers of >100 W. For example, a laser driver providing a peak current of 60 A can drive four laser diode channels, each with 13 A, for, for example, 40 W peak power per channel, for a total of 160 W peak power.

[0081] While several embodiments have been described in detail, by way of example, the laser drivers of the embodiments described herein can be implemented as circuits comprising discrete components, as modules whose components are at least partially integrated into one or more functional blocks. In some embodiments, the components of the driver circuit can be provided as an integrated circuit module that combines the main current switch Qmain and the driver circuit on a single substrate. For example, the latter can be integrated into a module that is directly connected to a surface-mounted laser diode or laser diode array via low-inductance interconnects.

[0082] The use of fast, high-current GaN power transistors as current switching devices in direct-drive or resonant-drive pulsed laser drivers offers significant performance enhancements relative to conventional Si or SiC laser drivers, such as potentially orders of magnitude combined improvements in power and speed. For applications requiring lower power or lower speed, the circuit topologies disclosed herein for using GaN FETs for pulsed laser drivers to be directly driven with driver assist circuitry, and for using resonantly driven pulsed laser drivers, can alternatively be implemented using Si power MOSFETs or SiC power MOSFETs rather than one or more GaN power transistors. For example, as described above, the resonant driver circuit can be implemented using a fast, high-current GaN transistor for Q2 and Si or SiC technology for Q1. Furthermore, for example, in other embodiments, the driver assist circuitry can be configured to drive SiC power MOSFETs or Si power MOSFETs.

[0083] LIDAR Applications

[0084] Using laser drivers containing GaN power transistors for fast, high-current switching to deliver the high current levels and nanosecond or sub-nanosecond rise times required for long-range LiDAR requires high power, high frequency, and robust thermal performance.

[0085] The high-current ultrafast laser driver disclosed herein can be configured to drive a high-power laser diode (such as the Osram SPL DS90A_3) up to 120W at 40A. Multi-channel surface-mount (SMT) laser arrays for LiDAR systems (e.g., a quad-laser array of multiple laser diodes connected in parallel) enable LiDAR architectures with greater range and higher resolution. The additional channels increase the field of view and total peak power, with each channel capable of producing 120W. The ability to emit short pulses with nanosecond rise times while maintaining high peak power provides longer range and higher resolution, for example, driving all four channels at 40A, delivering 480W of peak power per channel. For new LiDAR designs, this peak power can be modulated at a low duty cycle to produce high-resolution 3D cloud points over long distances. For example, scanning LiDAR is a key technology for advanced driver assistance systems (ADAS) designed to improve road safety and enable autonomous driving. These electronic devices react immediately to potential collisions without wasting precious seconds of reaction time. Scanning LiDAR produces a high-resolution 3D image of the car's surroundings and registers obstacles early enough for ADAS or self-driving cars to initiate appropriate driving maneuvers, such as automatic braking, to prevent collisions.

[0086] While embodiments of the present invention have been described and illustrated in detail, it should be clearly understood that these embodiments are by way of illustration and example only and not limitation, the scope of the present invention being defined solely by the appended claims.

Claims

1. A circuit for driving a laser component, the circuit being configured to operate in a charging phase and a laser emission phase, wherein the laser component does not emit laser light during the charging phase and emits laser light during the laser emission phase, the circuit comprising: Inductors; a capacitor having a first terminal connected to a power source and a second terminal connected to a reference voltage source, the reference voltage being grounded; a first transistor and a second transistor connected in series between the inductor and the reference voltage source, the first transistor having a gate for controlling whether current flows from a drain to a source of the first transistor, the drain of the first transistor being connected to a first terminal of the capacitor via the inductor, the source of the first transistor being electrically coupled to the laser component, the second transistor having a gate for controlling whether current flows from the drain to the source of the second transistor, the drain of the second transistor being directly connected to the source of the first transistor, and the source of the second transistor being connected to the reference voltage source; a first gate driver connected to the gate of the first transistor to control whether the first transistor is turned on or off, the first gate driver configured to keep the first transistor turned on during both the charging phase and the laser emission phase; a second gate driver connected to the gate of the second transistor to control whether the second transistor is turned on or off, the second gate driver being configured to keep the second transistor on during the charging phase but to turn off the second transistor during the laser emission phase, The circuit is configured such that: In the charging phase, charge is provided to the first terminal of the capacitor, and current flows through the inductor, the first transistor, the second transistor, and into the reference voltage source; During the laser emission phase, current flows through the inductor and the first transistor, but does not flow through the second transistor and is transferred to the laser component, thereby providing a current pulse to the laser component.

2. The circuit of claim 1, the laser component comprising a four laser diode array.

3. The circuit of claim 1 , the laser component being within a current path extending from the source of the first transistor to the reference voltage source, the current path being a path that diverts current when the second gate driver turns off the second transistor during the laser emission phase.

4. The circuit of claim 3 , the capacitor being a first capacitor, the circuit further comprising a second capacitor and a diode connected in the current path between the source of the first transistor and the laser component, such that the second capacitor is connected between the source of the first transistor and an anode of the diode. 5 . The circuit of claim 4 , further comprising an energy recovery component connected between the second capacitor and the first capacitor, the recovery component configured to provide charge from the second capacitor to the first capacitor during the charging phase.

6. The circuit of claim 4, wherein the diode is a first diode, and the laser component comprises: A second diode is a laser diode having an anode connected to a cathode of the first diode, the laser diode having a cathode connected to the reference voltage source.

7. The circuit of claim 6, further comprising a third diode having an anode connected to the cathode of the laser diode, the third diode having a cathode connected to the anode of the laser diode.

8. The circuit of claim 6, wherein the laser diode is a four-laser diode array.

9. The circuit of claim 1 , configured to generate current pulses to the laser component having a rise time in the sub-nanosecond to nanosecond range, a pulse duration in the sub-nanosecond to tens of nanoseconds range, and a peak current of ≥100 A.

10. The circuit of claim 1, configured to generate current pulses to the laser component having a nanosecond rise time, a nanosecond pulse duration, and a peak current of 170A.

11. The circuit of claim 7, the laser component comprising a four laser diode array.

12. A method for operating a circuit for driving a laser component, the circuit being configured to operate in a charging phase and a lasing phase, wherein the laser component does not emit laser light during the charging phase and emits laser light during the lasing phase, the circuit comprising an inductor; a capacitor having a first terminal connected to a power supply and a second terminal connected to a reference voltage source, the reference voltage being grounded; a first transistor and a second transistor connected in series between the inductor and the reference voltage source, the drain of the first transistor being connected to the first terminal of the capacitor via the inductor, the source of the first transistor being electrically coupled to the laser component, the drain of the second transistor being directly connected to the source of the first transistor, and the source of the second transistor being connected to the reference voltage source; the method comprising: During the charging phase, charge is provided to the first terminal of the capacitor by turning on the first transistor and turning on the second transistor, so that current flows in series through the inductor, the first transistor, the second transistor, and into the reference voltage source; as well as During the laser emission phase, the first transistor is kept on but the second transistor is turned off, so that current flows through the inductor, the first transistor, and is transferred to the laser component, thereby providing a current pulse to the laser component.

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