Patent Application
20210116564
The present disclosure relates to a Light Detection and Ranging (LiDAR) system, and more particularly to, voltage generators and methods for supplying voltages to one or more electronic devices of the LiDAR system.
LiDAR systems have been widely used in autonomous driving and high-definition map creation. A typical LiDAR system measures the distance to a target by illuminating the target with pulsed laser light using a scanner and detecting the reflected light pulses with a photodetector. Differences in light return times and wavelengths can then be used to calculate the distance to the target. The distance, coupled with known information such as the direction of the light and the location of the scanner, can be used to make digital three-dimensional (3D) representations of the target (e.g., a point cloud). The laser light used for LiDAR scan may be ultraviolet, visible, or near infrared. In a typical LiDAR system, a narrow laser beam is used as the incident light to map physical features, which can achieve a very high resolution. Such a LiDAR system is particularly suitable for applications such as high-definition map surveys and 3D sensing in autonomous driving.
In a LiDAR system, various electronic devices require low noise, high voltage power supplies. For example, high sensitivity photodetectors for detecting the reflected light pulses require a low noise bias voltage up to +/− several hundreds of volts. Generating such a high voltage from a low voltage input is challenging. Conventional approaches using boost or flyback switching DC-DC converters generally require inductors and/or transformers along with a high-performance IC to facilitate the required switching operations. Due to the use of electromagnetic components (e.g., inductors, transformers, etc.) and fast current switching devices, such conventional voltage generation circuitries tend to generate high electromagnetic interferences (EMI) that would degrade the sensitivity of the photodetectors. In addition, conventional voltage generation schemes suffer from a low conversion efficiency (typically <10%) due to a low load current (e.g., the bias current of a typical photodetector is usually less than 0.5 mA). With low conversion efficiencies, excessive heat would be generated that would further degrade the performance of the photodetectors. Moreover, the overall bill of materials (BOM) is usually quite high (estimated>$10) due to the high cost of the electromagnetic components and high-performance switching devices.
Embodiments of the disclosure address the above problems by improved voltage generators having low noise and high efficiency without using any inductors or transformers.
Embodiments of the disclosure provide a voltage generator for supplying a voltage to an electronic device of a LiDAR system. The voltage generator includes a clock source configured to generate a clock signal and a voltage source configured to generate a first voltage signal having a first voltage level. The voltage generator also includes a voltage multiplier coupled to the voltage source and the clock source. The voltage multiplier is configured to generate a second voltage signal having a second voltage level based on the first voltage signal and the clock signal. The second voltage level is higher than the first voltage level.
Embodiments of the disclosure also provide a method for generating a voltage to power an electronic device of a LiDAR system. The method includes generating, by a clock source, a clock signal. The method also includes generating, by a voltage source, a first voltage signal having a first voltage level. The method further includes generating, by a voltage multiplier, a second voltage signal having a second voltage level based on the first voltage signal and the clock signal. The second voltage level is higher than the first voltage level.
Embodiments of the disclosure further provide a LiDAR system. The LiDAR system includes a light source configured to emit a light beam, a scanner configured to project the light beam to an object, and a photodetector configured to detect a reflected light beam reflected from the objected. The LiDAR system also includes a voltage generator configured to supply a voltage to at least one of the light source, the scanner, or the photodetector. The voltage generator includes a clock source configured to generate a clock signal and a voltage source configured to generate a first voltage signal having a first voltage level. The voltage generator also includes a voltage multiplier coupled to the voltage source and the clock source. The voltage multiplier is configured to generate a second voltage signal having a second voltage level based on the first voltage signal and the clock signal. The second voltage level is higher than the first voltage level. The voltage multiplier is also configured to supply the second voltage signal to at least one of the light source, the scanner, or the photodetector.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
As illustrated in
Consistent with some embodiments, LiDAR system 102 and sensor 110 may be configured to capture data as vehicle 100 moves along a trajectory. For example, a scanner of LiDAR system 102 is configured to scan the surrounding area of vehicle 100 to acquire data for constructing 3D representations of objects in the surrounding area. For example, LiDAR system 102 can measure the distance to a target by illuminating the target with pulsed laser light using the scanner and detecting the reflected pulses with a photodetector. Differences in light return times and wavelengths can then be used to calculate the distance to the target. The distance, coupled with known information such as the direction of the light and the location of the scanner, can be used to make digital 3D representations of the target. The laser light used for LiDAR system 102 may be ultraviolet, visible, or near infrared. In some embodiments of the present disclosure, LiDAR system 102 may capture point clouds as a form of the digital 3D representations. As vehicle 100 moves along the trajectory, LiDAR system 102 may continuously capture data. Each set of data captured at a certain time range is known as a data frame.
As illustrated in
Consistent with the present disclosure, vehicle 100 may include a local inside body 104 of vehicle 100. Controller 112 may communicate with a remote computing device, such as a server, (not illustrated in
Light source(s) 206 used in transmitter 202 may be high power, low divergence laser source(s). In some embodiments, light source(s) 206 may require a supply voltage in the range of about 10-100 volts. Voltage generator 220 connected to a light source 206 may provide the required supply voltage with low noise. For example, voltage generator 220 may supply pulsed voltage power to drive light source 206. Light source 206 may then convert the pulsed voltage power to pulsed laser beams (e.g., in the ultraviolet, visible, or near infrared wavelength range) and emit the pulsed laser beams, which may be guided to scanner 210 for projecting to an object 212.
In some embodiments of the present disclosure, light source(s) 206 may include a fiber laser. A fiber laser may be a laser device in which the active gain medium is an optical fiber doped with rare-earth elements, such as erbium (Er), ytterbium (Yb), neodymium (Nd), dysprosium (Dy), praseodymium (Pr), thulium (Tm), and holmium (Ho). A fiber laser can have a high output power and high optical gain, such as having several kilometers long active regions, because of fiber's high surface area to volume ratio, which allows efficient cooling. A fiber laser can also have high optical quality because fiber's waveguiding properties reduce or eliminate thermal distortion of the optical path, typically producing a diffraction-limited, high-quality laser beam. Depending on the doped rare-earth elements, the wavelength of a laser beam provided by a fiber laser may be above 1,100 nm, such as 1,047 nm, 1,053 nm, 1,062 nm, 1,064 nm, 1,320 nm, 1,550 nm, between 1,570 nm and 1,600 nm, or between 1,750 nm and 2,100 nm. In some embodiments, a wavelength converter may be used to convert the wavelength of the laser beam provided by a fiber laser to below 1,100 nm in order to be detected by silicon-based photodetectors.
In some embodiments of the present disclosure, light source(s) 206 may include a diode laser. A diode laser may be a semiconductor device similar to a light-emitting diode (LED) in which the laser beam is created at the diode's junction. In some embodiments of the present disclosure, a diode laser includes a PIN diode in which the active region is in the intrinsic (I) region, and the carriers (electrons and holes) are pumped into the active region from the N and P regions, respectively. Depending on the semiconductor materials, the wavelength of a laser beam provided by a diode laser may be smaller than 1,100 nm, such as 405 nm, between 445 nm and 465 nm, between 510 nm and 525 nm, 532 nm, 635 nm, between 650 nm and 660 nm, 670 nm, 760 nm, 785 nm, 808 nm, or 848 nm.
Scanner 210 may be configured to project a light beam 209 (e.g., a pulsed laser beam emitted by light source 206) to an object 212 along a projection direction. Scanner 210 may scan object 212 using multiple light beams (including light beam 209) along multiple projection directions within a scan angle and at a scan rate. Object 212 may be made of a wide range of materials including, for example, non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules. The wavelength of light beam 209 may vary based on, for example, the composition of object 212. At each time point during the scan, scanner 210 may project a light beam (e.g., light beam 209) to object 212 along a projection direction within the scan angle. The projected light beam may also be referred to as an incident light and the corresponding projection direction may also be referred to as an incident direction. In some embodiments of the present disclosure, scanner 210 may also include optical components (e.g., lenses, mirrors, etc., not shown) that can focus the light beam emitted by light source 206 into a narrow light beam to increase the scan resolution and range.
Scanner 210 may include a scanner driver, such as a MEMS driver, to drive the optical components used for focusing the light beam emitted by light source 206. In some embodiments, the scanner driver may require a supply voltage (e.g., MEMS driver voltage) in the range of about 100-200 volts. Voltage generator 220 connected to scanner 210 may provide the required supply voltage with low noise.
When light beam 209 is projected to object 211, light beam 209 can be reflected by object 212 via backscattering, such as Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence. Receiver 204 may be configured to detect a reflected light beam 211 (e.g., a reflected laser beam) reflected from object 212 along a reflection direction. Receiver 204 can then convert the optical energy of reflected light beam 211 into electrical energy and output an electrical signal 218 indicating the intensity of reflected light beam 211. In some embodiments, receiver 204 may include a lens 214 configured to collect light from a respective direction in its field of view (FOV). At each time point during the scan, a reflected light beam 211 may be collected by lens 214. Reflected light beam 211 may be reflected from object 212 and have the same wavelength as light beam 209.
In some embodiments, photodetector 216 may be a silicon-based photodetector, which includes silicon PIN photodiodes that utilize the photovoltaic effect to convert optical power into an electrical current. Silicon-based photodetector may be used to detect light beams having a wavelength below 1,100 nm. In some embodiment, photodetector 216 may be a Ge/InGaAs-based photodetector, which can detect light beams having a wavelength above 1,100 nm.
In some embodiments, photodetector 216 may require a bias voltage in the range of 100-200 volts or −100 to −200 volts. Voltage generator 220 connected to photodetector 216 may provide the required bias voltage. As used herein, positive and negative voltages are voltage values relative to the ground or neutral. The term “high voltage” refers to a high voltage difference relative to the ground/neutral. In other words, the absolute value of a voltage is used to determine whether the voltage is a high voltage. Therefore, both +200 V and −200 V may be considered as high voltages, while +100 V is lower than +200 V and −100 V is lower than −200 V. Similarly, the term “voltage level” refers to the voltage difference relative to the ground/neutral or the absolute value of a voltage. For positive voltage values, for example, +200 V has a higher voltage level than +100 V. For negative voltage values, for example, −200 V is considered to have a higher, not lower, voltage level than −100V. Voltage generator 220 may be configured to provide both positive and negative voltages to bias photodetector 216.
Voltage generators 220 connected to different components of LiDAR system 102 (e.g., light source 206, scanner 210, and photodetector 216) may be of the same kind, but configurable or programmable according to specific voltage requirements of the respective components or may be of different kinds (e.g., implemented using different components and/or circuitry). For ease of description, voltage generators are collectively denoted using reference number 220. It is understood that they may or may not be the same device.
As discussed above, high voltage power supplies are required to power various components (e.g., light source 206, scanner 210, photodetector 216, etc.) of LiDAR 102. In some cases, the required voltage may range from tens of volts to hundreds of volts. Generating such a high voltage from a low voltage input is challenging. Conventional approaches using boost or flyback switching DC-DC converters generally require inductors and/or transformers along with a high-performance IC to facilitate the required switching operations. For example,
Embodiments of the present disclosure provide an improvement voltage generator 220 to address the above problems.
Voltage source 304 may be configured to generate a first voltage signal having a first voltage level. For example, voltage source 304 may generate a Vdd signal (the first voltage signal) having a relatively low voltage level (the first voltage level, e.g., 1.5V, 5V, etc.). Voltage source 304 can be any suitable DC voltage source capable of generating a low-level voltage output. In some embodiments, voltage source 304 may be programmable to control the voltage level of the generated voltage signal. In some embodiments, voltage source 304 may receive a control signal from feedback controller 310 and control the voltage level of the generated voltage signal based on the control signal.
Voltage multiplier 306 may be coupled to voltage source 304 and clock source 302 (either directly or through level shifter 308), as shown in
In some embodiments, clock signal generated by clock source 302 may be directly used by voltage multiplier 306. In such cases, clock source 302 may be directly coupled to voltage multiplier 306. In some embodiments, the voltage level of the clock signal may need to be shifted (e.g., increased) to, for example, Vdd before inputting to voltage multiplier 306. In such cases, level shifter 308 may be used. As shown in
Level shifter 308 may also be referred to as a logic-level shifter, and may include any suitable circuits configured to translate an input signal with one voltage level to another voltage level, for example, from an original voltage level of the clock signal to Vdd. The output voltage level (e.g., the voltage level to be shifted to) may be based on input from voltage source 304 (e.g., the first voltage level Vdd of the first voltage signal). For example, the output voltage level of level shifter 308 may track or follow the voltage level of the input from voltage source 304 such that when the voltage level of the first voltage signal changes, the output voltage level of level shifter 308 also changes accordingly. Level shift 308 may be implemented by a fixed function level shifter IC (e.g., translating an input voltage level to one or more fixed output voltage levels) or a configurable mixed-signal IC (e.g., translating an input voltage level to a configurable output voltage level, such as based on a control signal from another input). In some embodiments, level shifter 308 may be implemented using an OTS IC.
In some embodiment, the clock signal generated by clock source may include a plurality of pulses. For example, the plurality of pulses may by in the form of a square wave, a sinusoidal wave, a triangular wave, or the like. The plurality of pluses generated by clock source 302 may have an original voltage level (e.g., represented by the height of the pulses), frequency f, and duty cycle τ. Level shifter 308 may shift the height of the pulses to the first voltage level based on the input from voltage source 304. In some embodiments, level shifter may retain the frequency f and the duty cycle τ of the clock signal.
Voltage multiplier 306 may be implemented by any suitable circuits for converting a low voltage signal to a high voltage signal.
During operation, voltage multiplier 306 may increase the voltage level along its multiple stages. For example, when pulse train 410 is low and pulse 420 is high, capacitor 406 is charged by the input voltage Vdd (provided by voltage source 304) through diode 404. Capacitor 406 may be charged to Vdd. Then, pulse train 410 becomes high and pulse train 420 becomes low. This brings the voltage level at the junction between diode 404 and capacitor 406 to 2Vdd, which then charges the capacitor of the next stage through the diode of the next stage. In this way, at each stage the voltage level is increased by Vdd. The output voltage Vout is, in theory, the number of stages N multiplied by Vdd. In practice, however, due to the voltage drop across diodes and parasitic capacitance (acting as a voltage divider together with the capacitor), the output voltage may be lower than N×Vdd. In general, the output voltage Vout is proportional to N×Vdd. Therefore, the output voltage may be controlled through Vdd (e.g., by controlling voltage source 304).
The output current Iout is proportional to Vdd×Ccp×f, where Ccp is the capacitance value used in voltage multiplier 306, and f is the frequency of the clock signal (e.g., also the frequency of pulse trains 410 and 420 in the implementation shown in
In some embodiments, a feedback control mechanism may be used to control the output voltage Vout and/or output current Iout. The feedback control may be implemented by feedback controller 310, as shown in
Although a Dickson voltage multiplier is shown as an exemplary implementation of voltage multiplier 306 in
In step S502, clock source 302 may generate a clock signal. The clock signal may have a frequency f, a duty cycle τ, and an original voltage level. In some embodiments, the clock signal may be in the form of a pulse train, and each pulse may be a square wave, a sinusoidal wave, a triangular wave, or the like.
In step S504, voltage source 304 may generate a first voltage signal having a first voltage level. For example, the first voltage signal may be a DC voltage signal having a voltage level Vdd. Vdd may be used as the source voltage for inputting into voltage multiplier 306 and/or level shifter 308.
In step S506, voltage shifter 308 may shift the original voltage level of the clock signal generated by clock source 302 to the first voltage level (e.g., Vdd) based on the first voltage signal provided by voltage source 304. After the shifting, the clock signal may retain its frequency and/or duty cycle, while having its original voltage level adjusted to the first voltage level (e.g., Vdd).
In step S508, voltage shifter 308 may supply the clock signal 320 (after voltage level shifting) to voltage multiplier 306. The supplied clock signal 320 may be used to control the increasing or multiplication of source voltage Vdd by voltage multiplier 306.
In step S510, voltage multiplier 306 may generate a second voltage signal having a second voltage level based on the first voltage signal (e.g., Vdd) and clock signal 320. For example, voltage multiplier 306 may use various kind of voltage multiplication and/or charge pumping circuits to increase the source voltage level Vdd provided by voltage source 304. The voltage multiplication and/or charge pumping may be controlled by clock signal 320. In the example shown in
In step S512, voltage multiplier 306 may supply the second voltage signal (e.g., output voltage Vout) to an electronic device (e.g., light source 206, scanner 210, photodetector 216, etc.) of LiDAR system 102. Depending on the requirements of the electronic device(s), individual electronic devices may be powered by separate voltage generators or multiple electronic devices may share a single voltage generator.
In step S514, one or more sensors (e.g., ambient light sensor 312, temperature sensor 314, voltage sensor 316, etc.) may sense an operation status or an operation environment of voltage generator 220. For example, ambient light sensor 312 may sense the intensity of the ambient light. In another example, temperature sensor 314 may sense the temperature in the environment of LiDAR system 102. In a further example, voltage sensor 316 may sense the ripples or noise in the output voltage Vout.
In step S516, the one or more sensors may generate a sensing signal indicating the operation status or the operation environment of the voltage generator and send the sensing signal to feedback controller 310. For example, ambient light sensor 312 may generate an ambient light intensity signal indicating the intensity of the ambient light. In another example, temperature sensor 314 may generate a temperature signal indicating the temperature in the environment of LiDAR system 102. In a further example, voltage sensor 316 may generate a signal indicating the level of ripples or noise in the output voltage Vout. Each of these sensing signals may be sent to feedback controller 310 for further processing.
In step S518, feedback controller 310 may generate a control signal based on the received sensing signal. For example, when the sensing signal indicates that the ambient light is low (e.g., at night time), feedback controller 310 may generate a control signal to control voltage source 304 such that Vdd is adjusted (resulting in the change of Vout) according to the low ambient light condition. In another example, when the sensing signal indicates that large ripples or noise is present in the output voltage, which may indicate that the output current is insufficient, feedback controller 310 may generate a control signal to control the frequency of the clock signal such that more charges are pumped to the output (e.g., by increasing the number of charging cycles per unit time). In a further example, when the sensing signal indicates that the temperature of light source 206 is high, feedback controller 310 may generate a control signal to control voltage source 304 such that a lower Vdd is provided to voltage multiplier 306, resulting in a lower output voltage Vout to drive light source 206.
In step S520, voltage source 304 and/or clock source 302 may adjust their outputs based on the control signal received from feedback controller 310 to close the feedback control loop. Method 500 may loop back to step S502 or S504, depending on which type of output is adjusted.
Embodiments of the present disclosure provide an improvement voltage generator 220 to generate high voltages using voltage multipliers or charge pumps. The improved voltage generator 220 can provide a stable DC output voltage based on a low-level source voltage (e.g., Vdd) and an alternating control signal (e.g. the clock signal). In this way, a low amplitude clock signal voltage is rectified to generate a high DC output voltage with passive unidirectional devices such as diodes. The clock signal can be provided by a programmable clock source 302 to achieve the optimum conversion efficiency for specific load conditions through frequency adjustment (e.g., adjusting clock signal frequency f). For a particular charge pump/voltage multiplier topology adopted to implement voltage multiplier 306 (e.g. a fixed architecture, the fixed number of elements, etc.), the voltage amplitude of the clock signal can also be adjusted (e.g., by adjusting Vdd) to generate different output voltage levels. No electromagnetic devices such as inductors or transformers are used, and no fast switcher devices such as switching ICs are used. As a result, the EMI generation and BOM (e.g. estimated <$5) are both much lower than the conventional approaches (e.g., shown in
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and related methods.
It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
