LiDAR modules can improve the speed of autonomous driving safety

The advent of autonomous driving has decisively expanded the presence of Laser Imaging Detection and Ranging (LiDAR) sensors in automotive electronics platforms. LiDAR works on the radar principle, but uses light pulses from infrared laser diodes.

Maxim Integrated’s new MAX40026 high-speed comparator and MAX40660/MAX40661 high-bandwidth transimpedance amplifiers (TIAs) provide a breakthrough in LiDAR technology by doubling the bandwidth and adding 32 channels (for a total of 128 instead of 96) in the same size LiDAR module.

What is LiDAR?

Maurizio Gavardoni of Maxim demonstrated an evaluation board for a four-channel LiDAR receiver system. It includes First Sensor's optical photodiodes and Maxim's new TIA and high-speed comparators.

In addition to AI, cameras, and radar, sensors are essential for assisted and autonomous driving. Because they provide accurate measurements of objects and detect obstacles in the road—fallen branches, other cars, even children running into traffic—LiDAR sensors have helped drive the adoption of advanced driver assistance systems (ADAS) and are essential to the development of autonomous vehicles (AVs). An AV’s perception of its surroundings must be extremely precise, which is why experimental robot cars are packed with sensors. The use of laser lighting systems allows autonomous vehicles to operate in low-visibility or no-visibility conditions and even without road markings.

“LiDAR sensors are playing an increasingly important role in vehicle sensor fusion because they provide accurate distance measurements of objects,” said Maurizio Gavardoni, principal member of the technical staff at Maxim Integrated. “A typical LiDAR sensor sends pulses of light that are reflected by objects and detected by a photodiode, allowing you to map the surrounding environment.”

LiDAR systems are based on time of flight (ToF), which measures precise timing events (Figure 1). Recent developments have seen several multi-beam LiDAR systems that can generate an accurate 3D image of the vehicle’s surroundings. This information is used to select the most appropriate driving maneuvers.

Figure 1: Time-of-flight functional diagram (Image: Maxim Integrated)

Figure 2 shows the basic layout of a LiDAR sensor. There are two basic types of LiDAR systems: micro-pulse LiDAR and high-energy LiDAR. Micro-pulse systems have evolved with the continuous increase in computing power and advances in laser technology. These new systems use very low power, around 1 W, and are completely safe for most applications. High-energy LiDAR, on the other hand, is common in atmospheric monitoring systems, where sensors are used to detect atmospheric parameters such as altitude, stratification, and cloud density.

Figure 2: General layout of a LiDAR sensor showing the main electronics (Image: Maxim Integrated)

“Automotive autonomous driving systems are evolving from 35 mph to 65 mph and beyond, but faster autonomous driving systems are essential,” Gavardoni said. “The challenge of meeting these needs [translates into] high-precision distance measurement of objects, [requiring] higher accuracy, more channels to fit in space-constrained platforms, [and meeting] stringent safety requirements.”

LiDAR Hardware

In a LiDAR project, the transimpedance amplifier is the most critical part of the electronic layout. Low noise, high gain, low group delay, and fast recovery from overload make the new Maxim TIA an ideal choice for distance measurement applications.

TIA circuits are often used in applications that require circuitry to buffer and scale the output of an electro-optical solution to achieve high speed and high dynamic range. A TIA is a current-to-voltage converter implemented almost entirely with one or more operational amplifiers (Figure 3).

Figure 3: General layout of a TIA with reverse polarized photodiodes (Image: Wikipedia)

Phototransistors and photodiodes are closely related and convert incident laser light into an electrical current. To maximize the performance of these devices, designers must pay special attention to interface circuits, wavelength, and optomechanical alignment. The MAX40660/MAX40661 transimpedance amplifiers enable faster, high-resolution self-driven systems. TIAs can reduce current consumption by more than 80% in low-power mode. For the MAX40660, Maxim's TIA supports 128 channels with a bandwidth of 490 MHz and a noise density of 2.1-pA/√Hz to provide higher measurement accuracy (Figure 4).

Figure 4: MAX40660 block diagram (Image: Maxim Integrated)

Meanwhile, the MAX40026 is a single-supply high-speed comparator for TOF distance measurement applications. Its low propagation delay dispersion of 10 picoseconds helps accurately detect fixed and moving objects. "Lower dispersion delay and more channels per system enable more precise timing measurements, which improves system resolution and enables higher drive speeds," said Gavardoni.

The MAX40026 has an input common-mode range of 1.5 V to VDD + 0.1 V, which is compatible with the output swings of many widely used high-speed TIAs. The low-voltage differential signaling (LVDS) output stage minimizes power consumption and interfaces directly with many FPGAs and CPUs (Figure 5).

Figure 5: MAX40026 functional diagram (Image: Maxim Integrated)

The new solutions have been further reduced in size, allowing more channels to be inserted into space-constrained vehicle platforms. These ICs meet the most stringent safety requirements of the automotive industry – with AEC-Q100 qualification, improved electrostatic discharge (ESD) performance, and force and diagnostic analysis (FMEDA) – to support system-level ISO 26262 certification.