WO2019088974A1

WO2019088974A1 - Power circuit and method for a laser light source of a flash lidar sensor

Info

Publication number: WO2019088974A1
Application number: PCT/US2017/059017
Authority: WO
Inventors: Sebastian Heinz
Original assignee: Continental Automotive Systems Inc
Current assignee: Continental Automotive Systems Inc
Priority date: 2017-10-30
Filing date: 2017-10-30
Publication date: 2019-05-09
Anticipated expiration: 2020-04-30

Abstract

A lidar sensor assembly includes a power input and a laser light source. The lidar senor assembly also includes a synchronous buck converter electrically connected to the power input and the laser light source and configured to provide a pulsed power output to the laser light source.

Description

POWER CIRCUIT AND METHOD FOR A LASER LIGHT SOURCE

OF A FLASH LIDAR SENSOR

TECHNICAL FIELD

[0001] The technical field relates generally to electrical circuits for powering a flash lidar sensor assembly.

BACKGROUND

[0002] Flash lidar systems often employ laser light sources, e.g., laser diodes, which are configured to generate pulses of light. In order to generate the light pulses, the laser light sources often require high operating currents, e.g., in the range of 150 A, with an average forward voltage of around 2 V.

[0003] Typically, a linear current source is utilized to supply the laser light source. Such a linear current source utilizes a plurality of large bulk capacitors electrically connected in parallel with one another. These capacitors ensure the high peak currents demanded by the laser light source. The capacitors are charged during the pause time (i.e., the off time) of the laser pulse. Switching of the current is performed by a plurality of MOSFETs disposed in parallel with one another and in series with the laser light source and used in their linear mode.

[0004] However, such linear current sources have several disadvantages. One disadvantage is excessive heat generation due to efficiencies of around 15%. Compensating for the heat generation requires large housings and heat sync structures in order to dissipate the heat and avoid damaging this and other circuits. This is particularly disadvantageous in automotive applications, where space for sensing elements is severely limited.

[0005] Further, a high amount of ripple current is applied to the capacitors. In order to ensure reliability in the harsh automotive environment, as many as 10 capacitors may be required in parallel, to keep ripple current in the range of 1.5 A.

[0006] As such, it is desirable to present a lidar sensor assembly with a more efficient power supply circuit with less ripple current. In addition, other desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. BRIEF SUMMARY

[0007] In one exemplary embodiment, a lidar sensor assembly includes a power input and a laser light source. The lidar senor assembly also includes a synchronous buck converter electrically connected to the power input and the laser light source and configured to provide a pulsed power output to the laser light source.

[0008] In one exemplary embodiment, a method of operating a lidar sensor assembly includes receiving electrical power at a power input. The method also includes generating a pulsed power output with a synchronous buck converter. The pulsed power output has a higher current and a lower voltage than the electrical power received at the power input. The method further includes producing a light pulse with a laser light source from the pulsed power output generated by the synchronous buck converter.

[0009] In one exemplary embodiment, a vehicle includes a flash lidar sensor assembly. The assembly includes a power input and a laser light source. The assembly also includes a synchronous buck converter electrically connected to the power input and the laser light source and configured to provide a pulsed power output to the laser light source. The vehicle further includes a propulsion system, a steering system, and/or a braking system. A vehicle control system is in communication with the flash lidar sensor assembly and at least one of the propulsion system, the steering system, and/or the braking system. The vehicle control system is also configured to at least partially control the propulsion system, the steering system, and/or the braking system in response to data received from the lidar sensor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Other advantages of the disclosed subject matter will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0011] Figure 1 is a block schematic diagram of a lidar sensor assembly according to one exemplary embodiment;

[0012] Figure 2 is a graph showing desired pulses of electrical current supplied to a laser light source according to one exemplary embodiment; [0013] Figure 3 is an electrical schematic of a synchronous buck converter for supplying electrical current to the laser light source according to one exemplary embodiment;

[0014] Figure 4 is a graph showing voltage and current consumption by the lidar sensor assembly during a pulse of laser light output according to one exemplary embodiment;

[0015] Figure 5 is a graph showing power consumption by the lidar sensor assembly and the laser light source during the pulse of laser light output according to one exemplary embodiment;

[0016] Figure 6 is a block diagram of a vehicle implementing the lidar sensor assembly according to one exemplary embodiment; and

[0017] Figure 7 is a flowchart showing a method of operating the lidar sensor assembly according to one exemplary embodiment.

DETAILED DESCRIPTION

[0018] Referring to the Figures, wherein like numerals indicate like parts throughout the several views, a lidar sensor assembly 100 is shown and described herein.

[0019] Referring to Figure 1, the lidar sensor assembly 100 of the exemplary embodiment includes a laser light source 102. In the exemplary embodiment, the laser light source 102 is configured to produce a pulsed laser light output, as described in greater detail below. The laser light source may include a solid-state laser, monoblock laser, semiconductor laser, fiber laser, and/or an array of semiconductor lasers. It may also employ more than one individual laser. The pulsed laser light output, in the exemplary embodiment, has a wavelength in the infrared range. More particularly, the pulsed laser light output has a wavelength of about 1064 nanometers (nm). However, it should be appreciated that other wavelengths of light may be produced instead of and/or in addition to the 1064 nm light.

[0020] In the exemplary embodiment, the duration of the pulse of laser light is about 300 μ8 and the begins about every 33.33 ms. As such, the lidar sensor assembly 100 of the exemplary embodiment produces about 30 light pulses per second. However, it should be appreciated that the duration and frequency of the light pulses may be different than those described herein. [0021] The lidar sensor assembly 100 may also include a diffusion optic 104 to diffuse the pulsed laser light output produced by the laser light source 102. The diffused, pulsed laser light output of the exemplary embodiment allows for the lidar sensor assembly 100 to operate without moving, e.g., rotating, the laser light source 102, as is often typical in prior art lidar sensors.

[0022] The lidar sensor assembly 100 may also include a controller 105 in communication with the laser light source 102. The controller 105 may include a microprocessor and/or other circuitry capable of performing calculations, manipulating data, and/or executing instructions (i.e., running a program). The controller 105 in the exemplary embodiment controls operation of the laser light source 102 to produce the pulsed laser light output.

[0023] The lidar sensor assembly 100 of the exemplary embodiment also includes a receiving optic 106, e.g., a lens (not separately numbered). Light produced by the laser light source 102 may reflect off one or more objects 107 and is received by the receiving optic 106. The receiving optic 106 focuses the received light into a focal plane (not shown). The focal plane is coincident with a plurality of light sensitive detectors 108. Each light sensitive detector 108 is each associated with a pixel (not shown) of an image (not shown).

[0024] At least one readout integrated circuit ("ROIC") 110 is bonded to the light sensitive detectors 108. The ROIC 110 is formed with a silicon substrate (not separately numbered) and includes a plurality of unit cell electronic circuits (hereafter "unit cells" or "unit cell") (not shown). In the exemplary embodiment, each unit cell is associated with one of the light sensitive detectors 108 and receives the electrical signal generated by the associated light sensitive detector 108. Each unit cell is configured to amplify the signal received from the associated light sensitive detector and sample the amplified output. The unit cell may also be configured to detect the presence of an electrical pulse in the amplified output associated with a light pulse reflected from the object 107. Of course, each unit cell may be configured to perform functions other than those described above or herein.

[0025] As stated above, in the exemplary embodiment, the light pulse has a duration of about 300 μ8. As such, a pulse 200 of electrical current, lasting about 300 μ8, must be provided to the laser light source 102. In the exemplary embodiment, about 150 amperes of current are required, as shown in Figure 2. As stated above, the pulse 200 begins about every 33.33 ms and, as such, has a frequency of about 30 Hz. However, it should be appreciated that different amounts of current, as well as different pulse 200 lengths and frequencies are also achievable.

[0026] Referring again to Figure 1, the lidar sensor assembly 100 includes a power input 112 to receive electrical power from a power source (not shown). As well appreciated by those skilled in the art, the power source may be a battery, a direct current ("DC") power supply, etc. In the exemplary embodiment, the voltage at the power input 112 is about 14 V.

[0027] In the exemplary embodiment, the lidar sensor assembly 100 also includes a power supply 113. The power supply may be implemented with a buck-boost converter (not separately numbered) with a input voltage range of 8-16 V and a limited current output of 0.5A. The power supply 113 limits inrush currents to the lidar sensor assembly 100.

[0028] The lidar sensor assembly 100 also includes a synchronous buck converter 114. In the exemplary embodiment, the synchronous buck converter 114 is electrically connected between the power supply 113 and the laser light source 102. The synchronous buck converter 114 is configured to provide a pulsed power output to the laser light source 102, as described in greater detail below.

[0029] Figure 3 shows an electrical schematic of the synchronous buck converter 114 according to one exemplary embodiment. The synchronous buck converter 114 includes at least one phase 300. In the exemplary embodiment, the synchronous buck converter 114 includes a plurality of phases 300, particularly three phases 300. However, it should be appreciated that, if suitable components are used, the synchronous buck converter 114 may utilize only one phase 300.

[0030] Each phase 300 of the synchronous buck converter 114 includes an inductor 302. In the exemplary embodiment, each inductor has an inductance of about 300 nH.

[0031] Each phase 300 also includes a first MOSFET 304 and a second MOSFET 306 for controlling electrical current through the inductor 302. More particularly, the first MOSFET 304 is a high side MOSFET with a duty cycle that specifies the electrical current through the inductor 302. The second MOSFET 306 acts as an ideal flyback diode.

[0032] The lidar sensor assembly 100 includes a controller 308 in communication with the synchronous buck converter 114. The controller 308 is configured to control the power output of the synchronous buck converter 114. Particularly, the controller 308 of the exemplary embodiment is electrically connected to the gates of the various MOSFETs 304, 306 to control actuation of the MOSFETs 304, 306.

[0033] In the exemplary embodiment, the controller 308 is implemented with a 3 -phase synchronous step-down DC/DC controller, such as model No. LTC3829, manufactured by Linear Technology Corporation of Milpitas, California, U.S.A. However, it should be appreciated that other suitable devices may be utilized to implement the controller 308.

[0034] The lidar sensor assembly 100 may also include a sense resistor 310 in series with the laser light source 102 for sensing the current flowing through the laser light source 102. In the exemplary embodiment shown in Figure 3, the controller is in communication with the sense resistor 310. As such, the controller 308 may utilize the sensed current flowing through the laser light source 102 in controlling the power output of the synchronous buck converter 114. More particularly, during the duration of the pulse, the various MOSFETS 304, 306 of the phases 300 are cycled on and off to maintain the necessary current flow to the laser light source 102.

[0035] The synchronous buck converter 114 further includes at least one input capacitor 312 and at least one output capacitor 314. The at least one input capacitor 312 is disposed in parallel between the power input 110 and the at least one phase 300. The at least one output capacitor 314 is disposed between the at least one phase 300 and the laser light source 102.

[0036] In the exemplary embodiment, the at least one input capacitor 312 is implemented with four 470 μΡ polymer electrolytic capacitors and three 22 μΡ ceramic capacitors. The at least one output capacitor 314 is implemented with three 10 μΡ ceramic capacitors. However, it should be appreciated that other materials and capacitances of the capacitors 312, 314 may be contemplated.

[0037] Efficiency of the lidar sensor assembly 100 according to the exemplary embodiment is significantly higher when compared to a linear power supply. This higher efficiency allows for reduced power losses, which, in turn, allows for a smaller housing (not shown) of the lidar sensor assembly 100 and overall heat reduction.

[0038] Figure 4 illustrates the voltage and current characteristics of the input capacitors 312 of the exemplary embodiment during a pulse duration. Specifically, line 400 representing the voltage across the capacitors 312 and shows a very small voltage decline (from 14 V to 10 V) during the pulse duration. Line 402 shows the current flow from the capacitors 312 during the same pulse duration. This is in stark contrast to prior art lidar sensors utilizing a linear current source. In such prior art sensors, the voltage across input capacitors drops immediately after the pulse begins, and continues to steadily fall for the duration of the pulse.

[0039] Figure 5 shows the near constant power consumption during the pulse duration. Specifically, line 500 shows the power consumption of the assembly 100 as a whole of about 400 watts during the pulse duration. This is in contrast to the linear current source of the prior art, which exhibits a power consumption of greater than 1.2 kW at the beginning of the pulse. Line 502 shows the power consumption of just the laser light source 102.

[0040] Referring now to Figure 6, the lidar sensor assembly 100 may be implemented in a vehicle 600, such as an automobile (not separately numbered). It should be appreciated that the lidar sensor assembly 100 may be implemented in other types of vehicles, including, but not limited to, motorcycles, aircraft, and watercraft.

[0041] The vehicle 600 of the exemplary embodiment includes a propulsion system 602, a steering system 604, and a braking system 606. The propulsion system 602 may include, but is certainly not limited to, an engine (not shown), a motor (not shown), and a transmission (not shown), for propelling the vehicle 600. The steering system 604 controls the direction of travel of the vehicle 600 by, e.g., turning one or more wheels (not numbered) of the vehicle 600. The braking system 606 may include one or more brakes (not specifically shown) to slow one or more of the wheels of the vehicle 600.

[0042] A vehicle control system 608 is in communication with the flash lidar sensor assembly 100 and at least one of the propulsion system 602, the steering system 604, and/or the braking system 606 and configured to at least partially control the propulsion system 602, the steering system 604, and/or the braking system 606 in response to data received from the lidar sensor assembly 100. Said another way, the vehicle control system 608 may be configured to control autonomous or semi- autonomous driving of the vehicle 600, utilizing data received from the flash lidar sensor assembly 100.

[0043] A method 700 of operating the lidar sensor assembly 100, according to one exemplary embodiment, is shown in Figure 7. The method 700 includes, at 702, receiving electrical power at the power input 112. The method 700 also includes, at 704, generating a pulsed power output with the synchronous buck converter 114. The pulsed power output has a higher current and a lower voltage than the electrical power received at the power input 112. The method 700 also includes generating a light pulse with the laser light source 102 receiving the pulsed power output from the synchronous buck converter.

[0044] The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A lidar sensor assembly comprising:

a power input;

a laser light source;

a synchronous buck converter electrically connected to said power input and said laser light source and configured to provide a pulsed power output to said laser light source.

2. The lidar sensor assembly as set forth in claim 1, wherein said synchronous buck converter includes at least one phase.

3. The lidar sensor assembly as set forth in claim 2, wherein said at least one phase of said synchronous buck converter includes an inductor and a first MOSFET and a second MOSFET controlling electrical current through said inductor.

4. The lidar sensor assembly as set forth in claim 2, wherein said synchronous buck converter includes a plurality of phases.

5. The lidar sensor assembly as set forth in claim 4, wherein each phase of said synchronous buck converter includes an inductor and a first MOSFET and a second

MOSFET controlling electrical current through said inductor.

6. The lidar sensor assembly as set forth in claim 1, further comprising a controller in communication with said synchronous buck converter and configured to control the power output of said synchronous buck converter.

7. The lidar sensor assembly as set forth in claim 6, further comprising a sense resistor in series with said laser light source for sensing the current flowing through said laser light source.

8. The lidar sensor assembly as set forth in claim 7, wherein said controller is in communication with said sense resistor such that said controller may utilize the sensed current flowing through said laser light source in controlling the power output of said synchronous buck converter.

9. The lidar sensor assembly as set forth in claim 1, further comprising an output capacitor electrically connected in parallel with said laser light source.

10. The lidar sensor assembly as set forth in claim 1 , further comprising an input capacitor electrically connected in parallel with said power input.

11. The lidar sensor assembly as set forth in claim 1, further comprising a diffusion optic disposed in optical communication with said laser light source to diffuse light generated by said laser light source into a field of view.

12. The lidar sensor assembly as set forth in claim 11, further comprising: a detector array having a plurality of detectors configured to receive the light reflected from an object and produce an electrical signal in response to receiving the pulsed light; and

a readout integrated circuit ("ROIC") bonded to said detector array.

13. A method of operating a lidar sensor assembly comprising:

receiving electrical power at a power input;

generating a pulsed power output with a synchronous buck converter, the pulsed power output having a higher current and a lower voltage than the electrical power received at the power input; and

producing a light pulse with a laser light source from the pulsed power output generated by the synchronous buck converter.

14. A vehicle comprising:

a flash lidar sensor assembly, including

a power input;

a laser light source;

a propulsion system, a steering system, and/or a braking system; and

a vehicle control system in communication with said flash lidar sensor assembly and at least one of said propulsion system, said steering system, and/or said braking system and configured to at least partially control said propulsion system, said steering system, and/or said braking system in response to data received from said lidar sensor assembly.

15. The vehicle as set forth in claim 14, wherein said synchronous buck converter includes a plurality of phases.

16. The vehicle as set forth in claim 15, wherein each phase of said synchronous buck converter includes an inductor and a first MOSFET and a second MOSFET controlling electrical current through said inductor.

17. The vehicle as set forth in claim 14, wherein said flash lidar sensor assembly further includes a controller in communication with said synchronous buck converter and configured to control the power output of said synchronous buck converter.

18. The vehicle as set forth in claim 17, wherein said flash lidar sensor assembly further includes a sense resistor in series with said laser light source for sensing the current flowing through said laser light source and wherein said controller is in communication with said sense resistor such that said controller may utilize the sensed current flowing through said laser light source in controlling the power output of said synchronous buck converter.

19. The vehicle as set forth in claim 14, wherein said flash lidar sensor assembly further includes:

a diffusion optic disposed in optical communication with said laser light source to diffuse light generated by said laser light source into a field of view.

a detector array having a plurality of detectors configured to receive the light reflected from an object and produce an electrical signal in response to receiving the pulsed light; and

a readout integrated circuit ("ROIC") bonded to said detector array.