A comprehensive introduction to the disassembled solid-state lidar

The LeddarVu8 laser radar was disassembled this time. The parameters of the LeddarVu8 laser radar are as follows:

After more than ten years of dedicated research and development, LeddarTech technology has now become quite mature and can be applied to various commercial solutions such as advanced driver assistance systems (ADAS), traffic management, navigation positioning, liquid level measurement, etc.

LeddarTech meets the key sensor requirements of system developers and integrators when developing lidar applications: small size, low cost, low power consumption, high reliability, ruggedness and adaptability.

Transmitter: Optical lens

The laser emission lens part adopts the combination of collimating lens and diffraction lens. Reflective and transmissive collimating lenses are used in the beam delivery system to maintain the collimation of the beam between the laser resonator and the focusing optical element.

Reflective collimators generally use copper full-reflection mirrors, while transmissive collimators use zinc selenide lenses. The diffraction layers of different thicknesses are photoetched on the diffraction grating lens substrate. Through the diffraction relationship, light of different wavelengths or intensities are imaged at different positions, thereby achieving the splitting effect. It acts like a photon router, combining photons into a variety of shapes.

When the laser beam passes through the microstructure of the laser diffraction plate, the photons will be redirected by the various shapes on the laser diffraction plate, similar to the multi-line scanning of a rotating lidar.

The base of the diffraction grating is low-expansion glass or fused quartz, which is coated with aluminum, and then parallel lines are engraved on the aluminum film. The precision requirements of the diffraction grating are extremely high, and it is difficult to manufacture. It is generally used in astronomical instruments.

The laser diode for the emission part is supplied by Excelitas Technologies, one of the world's largest civilian laser diode companies with annual revenue of approximately $700 million and headquartered in Massachusetts, USA. The laser diode model is TPGEW1S09H, which belongs to the 225 micron series.

Excelitas Technologies uses metal sealed inner packaging and plastic capsule outer packaging design, which is much cheaper than industrial lasers and is suitable for mass-produced products.

TPGEW1S09H uses GaAs epitaxial wafers, InGaAs excitation layers, and 905-nanometer infrared lasers.

Receiving part

The receiving part mainly consists of a receiving lens and a photodiode array. The receiving lens seems to be a general focusing glass lens.

The photodiode array is S7509 from Hamamatsu, Japan, with the following parameters:

The S7509 uses a chip package that can be reflow soldered or SMT mounted, making it very suitable for mass production. The dark current is relatively small and the signal-to-noise ratio is relatively high. Hamamatsu also has linear APD arrays and single photon array products.

Circuit part: motherboard, transmitter board and receiver board

There is a Texas Instruments Class D power amplifier on the transmitter board. This chip is generally used for audio amplification and driving current-type loads such as speakers. It may be used to amplify current to power the laser diode. It is a rather strange design.

There are three main chips on the receiving board, including a Lattice PLD, which you can also call FPGA, model LCMOX3LF-2100E-6MG121C.

From the above picture, we can know that this FPGA belongs to the MachXO3 series, uses Flash configuration memory, has 2112 logical operation complexes, is the fastest type, has a 121-pin csfBGA package, and is a commercial-grade product.

The above figure is the internal framework of LCMOX3LF-2100E-6MG121C. The biggest difference from general FPGA is its built-in PLL phase-locked loop circuit. PLL (Phase Locked Loop): It is a phase-locked loop or phase-locked loop, which is used to unify and integrate clock signals to make high-frequency devices work normally, such as memory access data.

PLL is a feedback technology used in oscillators. For many electronic devices to work properly, they usually need the external input signal to be synchronized with the internal oscillation signal. Due to process and cost reasons, ordinary crystal oscillators cannot achieve very high frequencies. When high-frequency applications are required, there are corresponding devices VCO to achieve high frequencies, but they are not stable. Therefore, a phase-locked loop can be used to achieve a stable and high-frequency clock signal.

For pulsed LiDAR, high-precision clock is the key to ensure the accuracy of LiDAR detection distance. Leddar Tech has not yet launched ASIC, so it can only use FPGA instead.

The receiving board has an Atmel Flash MCU, model ATSAMS70N20-CFN, which is an MCU with built-in 1024Kbyte Flash and 384 Multi Port SRAM, packaged in 100-pin LQFP, and built-in ARM Cortex M7 core, which is the most powerful model in the ARM M series. The following figure shows the internal framework of ATSAMS70N20-CFN.

There are also eight Maxim's MAX3806s on the receiving board. The MAX3806 is an optical distance meter with a built-in 60K or 30K switching impedance, an attenuator and a preamplifier.

8 chips represent 8 receiving channels. MAX3806, MAX4311 and MAX1446 are used together. MAX4311 is a MUX/AMP. MAX1446 is a 10-bit fully differential analog input ADC with a bit rate of 60Mbps, built-in precision reference voltage, and 32-pin TQFP package. It is mainly used for ultrasound image generation and CCD image generation.

Flash solid-state lidar can be regarded as an image sensor. The above picture is an application example.

The motherboard is mainly for the power supply part. The core chip is a Murata LKDC55KAAA-205, which is a non-isolated DC/DC converter that can output 3A current and mainly supplies the transmitting part.

summary

After disassembly, it can be seen that PIN-type solid-state laser radar has standard mass-produced components to choose from except for the lens, with a low threshold and low cost, and can replace traditional low-pixel cameras in the future. But compared with cameras, laser radar can work all day and all night, rain, snow, fog, haze, day and night.

It is conceivable that more solid-state LiDAR products will appear in the future, and better-performing linear APD and single-photon LiDARs, with higher resolution, may further squeeze the living space of cameras. [End]