The Shanghai Auto Show is just around the corner.

This year, many car brands, such as Xiaopeng, Weilai, extreme Fox, R Automobile and so on, will carry them.LidarIt's a mass-produced model on autopilot.

On the issue of autopilot, Chinese car companies are collectively standing on the opposite side of Tesla this time.

Tesla believes that pure vision can achieve complete autopilot.

Today, mainstream Chinese car companies are starting to mass-produce self-driving programs with lidar.

Why is lidar a necessary sensor for L3 intelligent driving?

The perceptual task of autopilot is to build an accurate 3D environment model in real time.

Deep learning plus monocular and trinocular vision is impossible to accomplish this task.

The fatal defect of monocular / trinocular camera is that this kind of system must be identified before it can detect and know the information of the target. Target recognition (classification) and detection (Detection) are inseparable.

The cognitive range of the deep learning algorithm comes from the breadth and richness of the data set, but the data set is always limited, so the deep learning algorithm is bound to miss detection.

If the target cannot be identified, the system will assume that there is no obstacle ahead. This is the reason for most of Tesla's many accidents.

The above, that is to say, monocular / trinocular system missed detection is inevitable, so it can only be used in L2 systems.

L2 or above, there must be lidar, lidar will bring overwhelming security advantages.

In a sense, the role of lidar manufacturers can be regarded asSystem integrator。

The traditional laser industry can provide mature components including laser emitting and receiving parts. These components in the industry have more than 15 years of technological precipitation, such as 1550 nm laser receiving diodes.

Lidar companies have no more than three years of technical expertise in the field of laser diodes, so their main job is to design scanners.

Scanners can also purchase off-the-shelf products.

Such as Japan's Nidec polygon scanner, Mirrorcle's MEMS galvanometer.

To some extent, the threshold for the development of lidar products is not so high.

If lidar manufacturers want to master the core technology,Self-made scanner。

1、The collision between ideal and reality:The optimal solution of current lidar mass production

Ideal lidar technology is notFlashIt must be.

Flash lidar is almost perfect in terms of performance, ecology, cost, volume and vehicle gauge.

But at present, the bottleneck of Flash lidar is its poor performance, which is mainly due to the fact that the laser transmitter of Flash lidar is VCSEL array.

However, the power density of VCSEL array is far from comparable to that of traditional laser diodes. Once this bottleneck is broken, Flash lidar can sweep the market.

But at present, if Flash lidar is to achieve a breakthrough in mass production, it will at least be necessary.5 years。

Another technical route is silicon optoelectronic.FMCW lidarThe technology maturity is lower than that of Flash, and even if the technology is mature, the price is higher than that of Flash lidar.

FMCW lidar needs expensive femtosecond laser generator, and the tuner works in terahertz band. Even if it is mass-produced, the cost is much higher than that of Flash lidar.

At present, lidar scanners can be divided into two categories: mechanical and optical, and mechanical can be subdivided into two categories.Micro machine、MEMS和SLAM。

SLAM is relatively rare. At present, the main products in the market are micro-machinery and MEMS.

Micromachines can be subdivided into four categories, namelyRotary type(including rotating mirror and polygon scanning),Galvanometer type(Velarray) 、Polyprism和Voice coil type。

MEMSDivided intoMEMS galvanometer和 DMD micromirrorTwo categories.

MEMS galvanometer can be divided into three categories: piezoelectric, electromagnetic and electrostatic.

2、Why did the MEMS route emerge as a new force? A huge cost advantage

The development direction of lidar is towards the all-solid state of Flash.

Valeo is the only lidar manufacturer with mass production customers at present. The long-distance gauge-level products SCALA adopts rotating mirror design, and the short-distance products use Flash.

However, Valeo's next generation of long-range SCALA is MEMS lidar. Why?

Valeo is the ancestor of vehicle gauge-grade rotating mirror lidar, and he is most aware of the disadvantage of rotating mirror lidar, which is that there is limited room for cost reduction.

At present, the SCALA second-generation rotating mirror lidar that Valeo is selling may cost less than $400.

Here, let's analyze the cost structure of lidar.

The cost of lidar can be divided intoBOM cost、production costs和Research and development cost。

Let's take a look at the BOM cost first.

Take Velodyne's Puck VLP-16 16-line lidar as an example, its retail price is $3800, and the cost of BOM is about $1000.

These are mainly laser emitting diodes and laser receiving diodes. 16 lines need 16 emitters and 16 receivers.

The price of the emitting diode is generally $20-25, such as Excelitas's TPGEW1S09H,905 nanometer, with a peak optical power of 70 watts, an input of 12V and a peak current of 30A.

The price of 1550 nm laser diode is about 3-5 times that of 905nm silicon laser diode, but its optical power is very low and is usually used in the field of laser communication.

In lidar, it is necessary to choose a more expensive 1550 nm fiber laser to achieve watt optical power, totaling about $580,740.

Electrical Machinery和ShellAnd the structural members are aboutFifty dollars，Circuit boardAboutOne hundred dollarsOptical devices such as optical lenses, filters and protective covers also cost more than $100.

The total BOM cost of such a mechanical rotary lidar is about $830,990.

Among the main components, two chips are more expensive.

One is the ADC08500, of Texas Instruments, which is a high-speed ADC, as high as 500MSPS, so the price is relatively expensive. The purchase scale of more than a thousand pieces is 30 US dollars per piece. This is the product line brought by Texas Instruments's acquisition of international semiconductors.

The other is the FPGA, model of Altera acquired by Intel, which costs about $14 for EP3C16U256C7N,.

There are mainly three chips on the back, and the FPGA, model of the main data processing chip Altera is EP3C25F324I7, which costs about $22.

There are also two pieces of memory, the price of which is estimated to be only $5.

There are some more expensive high-precision crystal oscillator, lidar is nanosecond products, clock accuracy requirements are extremely high. The precision of the components used is generally very high.

Chips and active components account for about $80, passive components account for $15, and PCB accounts for about $5.

The picture above shows the cost structure of a rotating mirror lidar such as Valeo's SCALA, with an annual output of 100, 000.

Its BOM costs about $300, and 12 additional transmitters and receivers are needed for 16 lines, or about $400.

This is already a scale with an annual output of 100,000.

The price is obviously a little high.

For MEMS lidar, transmitting and receiving lasers are greatly reduced, even if the equivalent of hundreds of lines, some only a few emission, reception can use single-line SiPM, can also use array, more flexible.

The cost of BOM has been greatly reduced, and its main cost is concentrated in the MEMS galvanometer. Mass production of MEMS galvanometer can be reduced to 30 to 50 US dollars, while the current purchase from outside is about 1000 US dollars.

Based on the difference between galvanometer and light source, the cost of MEMS lidar BOM is currently about$450 to $1200。

For Flash lidar, there is no scanner, high-power VCSEL and high-performance SPAD are in its infancy, the current prices are very high, 10-megapixel Flash lidar BOM about $7-1000.

Mass production can easily be reduced to less than $100 in the future.

So what are the disadvantages of MEMS?

The disadvantage is thatSignal-to-noise ratio和Effective distance及FOV is too narrow。

Because MEMS uses only one set of transmitting laser and receiving devices, the signal optical power must be much lower than that of mechanical lidar.

At the same time, the receiving aperture of MEMS lidar is very small, which is much lower than that of mechanical lidar, and the peak power of optical reception is proportional to the aperture area of the receiver, which leads to the further decrease of power.

This means that the ability of minimum signal detection is reduced, and at the same time, it also means that the effective distance is shortened.

The resolution of the scanning system is determined by the product of the mirror size and the maximum deflection angle, and the mirror size and the deflection angle are contradictory. The larger the mirror size, the smaller the deflection angle.

Finally, the cost and size of the MEMS galvanometer are also proportional. At present, the maximum size of the MEMS galvanometer is Mirrorcle, up to 7.5mm, and the price is as high as1199 dollars。

The MEMS micro-vibrating mirror developed by Xijing Technology, which is invested by Suteng Juchuang, has a diameter of 5mm and has entered the stage of mass production.

The MEMS microscopes used in PandarGT 3.0 of Hosai Technologies are provided by the self-research team.

Innoluce acquired by Infineon can also develop its own MEMS galvanometer.

According to the product list of Mirrorcle, the main supplier of MEMS galvanometer, it is obvious that the larger the size, the smaller the angle.

3、Electromagnetic MEMS galvanometer: the best choice for lidar

How to solve or improve this problem, that isElectromagnetic galvanometer。

According to the different driving modes, MEMS scanning mirrors can be divided intoElectrostatic drive、Electromagnetic drive、Piezoelectric drive和Electrothermal driveThere are four ways to drive.

Electrothermal drive is the use of electrical energy into thermal energy, and then converted into mechanical energy drive, its advantage is that the driving force and driving displacement is larger, but the response speed is slow.

Piezoelectric driveIt is driven by the piezoelectric effect of the piezoelectric material, which has the advantages of large driving force and fast response, but the piezoelectric material has the phenomenon of hysteresis.

Electromagnetic driveIt is driven by electromagnetic or permanent magnet, which has large driving force and driving displacement, but the disadvantage is that it may be subject to electromagnetic interference.

Electrostatic driveIt is driven by the electrostatic force between charged conductors, and has the advantages of low power consumption, high speed, good compatibility and so on. It is a widely used drive mode at present.

Electrostatic drive is a more mature way, the above Mirrorcle and some Israeli manufacturers are using electrostatic drive.

The electrostatic driven MEMS scanning mirror is made of monocrystalline silicon with simple process, mature process and low cost. The chip size is very small, the driving power consumption is very low, and the package is relatively simple, so it belongs to voltage-driven devices.

The disadvantage is that the force is also a little small, and is nonlinear, in addition, there is a suction phenomenon.

Electromagnetic driving force density is large, electromagnetic driven MEMS scanning mirror has also been widely used, its scanning angle is large, linear scanning can be achieved.

The electromagnetic drive device process involves the manufacture of solenoid coils with a thickness of tens of microns, the packaging needs to be equipped with permanent magnets, and the size of the device module is slightly larger.

The device is a current-driven device with a driving current of tens of milliamperes and high driving power consumption.

The device can work not only in the resonant state but also in the non-resonant state, and the driving power consumption can be greatly reduced in the working and resonant state.

The disadvantage of electromagnetic type is that the process is complex, the threshold is high, the cost is slightly higher, the volume is slightly larger, and the response speed is slightly slower than static electricity, so the response speed is not a problem.

Because the data processing ability of the back end is limited at present, the lidar data processing basically adopts the depth learning algorithm except the traditional algorithm, and also uses the lidar to identify the target and fuse with the vision sensor.

However, due to the huge amount of data, generally can only withstand 10-15Hz frame rate, electromagnetic can do 30Hz, static higher, but not significant.

Another electromagnetic interference problem is easy to solve, that is to increase magnetic shielding and increase the magnetic field density: using the strongest magnet NdFeB, namely NdFeB.

As for demagnetization, the Curie temperature of sintered NdFeB is 312 degrees Celsius. The higher the Curie temperature, the higher the working temperature of the magnetic material, and the better the temperature stability.

Sintered NdFeB raw materialThe addition of cobalt, terbium, dysprosium and other elements can increase the Curie temperature.

The working temperature of EH NdFeB can reach 200C, and the lower H can also reach 120C, which is enough to adapt to the vehicle environment.

The reliability of the MEMS mirror has been used as a target for attack, saying that the MEMS mirror is as fragile as potato chips.

The electrostatic type may be a little bit like this, but the electromagnetic type is different. it has a large volume and a higher strength of the cantilever, and the electromagnetic galvanometer can withstand the impact of more than 300g, far exceeding the 50g required by the car specification.

MEMS technology is widely used in inertial guidance systems in military and aerospace, which can withstand overload acceleration of more than 500g.

The time limit of this application field has been more than 30 years, and the technology has gradually shifted from military industry to civilian use, which is not a new technology.

In contrast, it is also difficult for the rotating motor used in mechanical lidar to achieve 50G anti-shock.

Actually, there are many MEMS products in the car, including gyroscope, accelerometer, pressure sensor, MEMS silicon microphone, AR-HUD and DMD galvanometer for headlights.

DMD galvanometer is the exclusive supply of Texas Instruments, namely DLP technology, DLP technology has been used for more than 20 years, there is no doubt about its reliability.

Lincoln Continent and navigators used Texas Instruments' early DMD chip DLP3030, with only 400 megapixels.

The Mercedes-Benz AR HUD uses Texas Instruments' latest DMD chip, DLP5531 (mass-produced in the second half of 2018, so Lincoln didn't use it). It has 1.3 megapixels, the FOV is 10X5 °, and the VID distance is 33 feet, or 10 meters, which Mercedes says is the equivalent of a 77-inch display.

Not only does Mercedes-Benz use DLP projection on HUD, but Mercedes-Benz also uses DLP projection, which is also DLP5531, in its headlights.

The temperature aspect is endorsed by the ultra-high temperature DLP projection, which is naturally not a problem. The actual MEMS galvanometer can be regarded as a semiconductor chip. Silicon-based semiconductors can easily range from minus 40 to 125 degrees Celsius.

The rotating motor used in mechanical lidar is due to lubricating oil:

The oil condenses into fat at low temperature, which makes it difficult to start or unable to start.

At high temperature, the oil will evaporate to the mirror, cycle more times, and will accumulate into oil droplets to interfere with the light path.

These two problems are common in mechanical radar at present. Valeo specifically added PTC heating and cooling facilities.

For traditional car factoriesCar gaugeIt is more important than performance, so Flash lidar is chosen at close range.

For Xinxing car factoryPerformanceMore important than the car rules, so choose Luminar, and between the two manufacturers choose MEMS, such as BMW, although Innoviz many difficulties, but BMW did not give up the MEMS route.

Because of the delivery problem, Innoviz had no choice but to choose the electrostatic galvanometer at the initial stage, but it is turning.Electromagnetic galvanometer。

Comprehensive consideration of performance, car specification, cost, volume, ecologyMEMS electromagnetic galvanometer lidarI am afraid it is the best choice for most manufacturers in these five years.