What Is LiDAR in Autonomous Driving Technology? – Points to Consider in Achieving High-Performance Sensing Function –

LiDAR (light detection and ranging) is a type of sensor using a laser beam. LiDAR emits a laser beam over a wide area and then precisely measures the time that the laser beam takes to return to the LiDAR after hitting and being reflected by an object. A combination of the direction in which the laser beam is emitted and the time the laser beam takes to return to the LiDAR gives the LIDAR the distance to an object. By repeating measurements with various directions of laser emission, the LiDAR is able to recognize the object. This is a technology essential to autonomous driving cars. It is expected that autonomous driving cars equipped with the LiDAR will increase year after year. This article will discuss the functions and system configuration of the LiDAR and will introduce the electronic components making up the LiDAR as well.

What is LiDAR?

LiDAR (light detection and ranging) refers to a sensing technology that is used to measure the time a laser beam emitted on an object takes to return to the LiDAR after being reflected by the object. The LiDAR incorporated in ADAS, AD systems, etc., is used in many cases to sense an object present in the surrounding area. In these systems, the LiDAR is used in combination with cameras, radars, sonars, etc. The LiDAR is operated by several types of optical axis varying methods (Table 1).

Method of distance measurement and object recognition

Distance measurement and object recognition are carried out using the following methods.

＜Distance measurement＞
A laser diode emits a laser pulse onto an object and a photodiode receives reflected laser light from the object. The distance to the object is determined based on the time between the point of light emission and the point of light reception.

＜Object recognition＞
Directions in which laser pulses are emitted and distances measured are plotted into a point cloud image. Using this image, the type of individual or object is identified. A point cloud refers to a set of points representing positional information on an object.

Using LiDAR

In-vehicle LiDAR is used mainly for the following three purposes.

Obstacle recognition
Recognize an obstacle from an obtained point cloud image.

Creating a dynamic map
Combine point cloud data with three-dimensional map data to create the dynamic map required for autonomous driving.

Grasping and correcting the vehicle position
Grasp the traveling position of the vehicle, an obstacle present in the surrounding area, etc., using the dynamic map, and correct the current position to a normal traveling position.

Trends in the LiDAR market

As autonomous driving cars grow in number and the level of autonomous driving improves further, cars equipped with LiDAR are expected to increase. The higher level of autonomous driving leads to a demand for LiDAR's sensing function with higher performance. Functions/performance that electronic components making up the LiDAR are required to offer in the future "higher power," "faster communication," and "smaller in size and weight." Details of these requirements are as follows.

●Higher power
Improving the precision of obstacle recognition requires that the obtained point cloud group be of finer points. When the amount of data processing increases due to higher resolution, power consumption within a semiconductor device, such as the main CPU, increases as well, thus supplying higher power to said semiconductor device is essential.

●Faster communication
Increasing data crunching creates a demand for high-frequency and high-speed transmission/processing capability.

●Smaller in size and weight
In addition to the above challenges, there is a need for reducing the size of electronic components.

System configuration of LiDAR

Overall configuration

A LiDAR system is composed of the following components. Fig. 1 shows the configuration of a LiDAR system.

●Laser diode: A laser diode generates a high-speed pulse current, emitting a laser beam pulse with a constant waveform and phase.

●Photodiode: A photodiode turns light into an electric signal. When receiving light, it generates a current and voltage. An amplifier is incorporated into a photodiode light-receiving circuit to amplify the output voltage from the circuit.

●FPGA: An FPGA is an integrated circuit that, even after being built into a product, can be reprogrammed to configure an intended logical circuit.

●MCU (microcomputer): An MCU gives a control instruction to an external ECU.
●Transceiver: A transceiver is a device or circuit that communicates with external equipment.
●Memory (DDR): A DDR is used as a buffer during data processing.
●Memory (flash): A flash memory stores control software and sensor data.
●DC/DC converter: A DC/DC converter converts a voltage from a battery into a voltage each electronic component or circuit needs.

Individual circuits and components

DC/DC converter

In a DC/DC converter circuit, in general, a conductive polymer hybrid aluminum electrolytic capacitor is used to eliminate noise at the input end and to smooth voltage output at the output end, an in-vehicle power inductor is used for voltage conversion, and a chip resistor (high-precision chip resistor) is used for voltage measurement.

【Components used】

Noise reduction, switching, and smoothing ―― Conductive polymer hybrid aluminum electrolytic capacitor

POINT

1. ❶ Its high capacitance, low ESR, and high ripple performance contribute to circuit miniaturization and higher power features (low voltage and high current).
2. ❷ Improved capacitance characteristics at high frequencies contribute to the elimination of noise, including high frequency components generated by high frequency switching of circuits over a wide band of frequencies.

Voltage conversion ―― Automotive power inductor

POINT

1. ❶ Contributes to circuit miniaturization and higher power features (low voltage and high current) due to the low loss and high current performance of metallic magnetic materials.
2. ❷ Improved loss characteristics (low ACR) at higher frequencies contribute to the suppression of losses in high frequency switching circuits.

Voltage measurement ―― Chip resistor (high-precision chip resistor)

POINT

1. ❶ Contributes to the high-precision control of circuit output characteristics through the low resistance tolerance and low TCR performance with a thin-film structure.

Transceiver I/F

As shown in Fig. 3, a transceiver circuit communicates with external equipment (CAN, Ethernet, etc.) through two lines. To run this circuit normally, you need to be careful with static electricity and noise. Static electricity or noise entering the circuit through the communication line affects the circuit and in a worst-case scenario, may cause its electronic component to fail. Usually, therefore, the circuit is provided with a chip varistor and an ESD suppressor serving as electrostatic control measures.

【Components used】

Static electricity measures ―― Chip varistor、ESD suppressor

POINT

1. ❶ Contributes to the suppression of electrostatic (ESD) noise while maintaining circuit communication quality with a lineup of products having a wide range of capacitance characteristics.
2. ❷ Chip varistors support low to high communication speeds with capacitance characteristics ranging from 8 to 250 pF.
3. ❸ ESD suppressors support high-speed communication speeds with their capacitance characteristics of 0.1 pF.

Photodiode light-receiving circuit

A photodiode outputs a current that is proportional in intensity to incoming light. Reflected laser light is weak and therefore needs to be amplified through an amplifier circuit. To construct an amplifier circuit with high precision, the circuit needs a high-precision chip resistor and a thermistor that compensates for temperature-dependent characteristic changes.

【Components used】

Signal amplification by an amplifier circuit (set amplification factor) ―― Chip resistor (high-precision chip resistor)

POINT

1. ❶ A chip resistor with a thin-film structure offers a small resistance tolerance and a low TCR, contributing to high-precision control of the output characteristics of the circuit.

Temperature compensation for a received light signal ―― NTC thermistor (chip type)

POINT

1. ❶ A thermistor is small, highly resistant to heat, and is formed by an original technique that offers high reliability, thus contributing to highly precise temperature compensation in the circuit.

Laser diode irradiation circuit

This irradiation circuit is simply composed of a laser diode, an FET (GaN), and a gate resistance. Because it emits large pulse currents at high speed, the FET (GaN) needs to be precisely switched on/off. Also, it is important to suppress switching noise caused by the FET (GaN). For that purpose, a gate resistance capable of handling a high-power operation must be used.

【Components used】

Suppressing gate-driving noise by the switching element ―― Chip resistor (small and high-power chip resistor)

POINT

1. ❶ With its original resistance pattern, electrode structure, etc., the chip resistor is small in size and yet handles high-power operations, thus contributing to a reduction in the size of the circuit.

Summary

As autonomous driving cars grow in number and the level of autonomous driving improves further, cars equipped with LiDAR are expected to increase. The higher level of autonomous driving has led to a demand for LiDAR's sensing function with higher performance. Sensor devices incorporated in cars, such as LiDAR, will increase in number and under no circumstances will not decrease in number. There is no doubt that electronic components used in such devices and circuits adjacent thereto will face these demands: "low loss," "large current," "high frequency," and "small size." Panasonic Industry offers a wide variety of product lineups for use in LiDAR (Table 2).

Component	Feature	Large current	Low loss	High frequency	Small size	High precision
Conductive polymer hybrid aluminum electrolytic capacitor	Low ESR High reliability	✔	✔	✔	✔
Automotive power inductor	Large current, low loss High reliability	✔	✔	✔	✔
Chip resistor (high-precision chip resistor) Chip resistor (small and high-power chip resistor)	High precision, high resistance to heat				✔	✔
Chip varistor	Small and light				✔
ESD suppressor	Low capacitance Ultrafast data I/F			✔	✔
NTC thermistor (chip type)	Small, high resistance to heat				✔	✔

Related product information

• Conductive polymer hybrid aluminum electrolytic capacitor
• Automotive power inductor
• Chip resistor (high-precision chip resistor)
• Chip resistor (small and high-power chip resistor)
• Chip varistor
• ESD suppressor
• NTC thermistor (chip type)

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