SLYY150D October   2018  – April 2025 OPA855 , OPA857 , OPA858 , OPA859

 

  1.   1
  2.   Overview
  3.   Detection and imaging in autonomous cars
  4.   Lidar types
  5.   The Lidar subsystem
  6.   Lidar system integration
  7.   Conclusion
  8.   Additional resources

Lidar system integration

For systems that require high density on further integration, TI offers lidar laser drivers for the Tx path and amplifiers that handle the connection in the Rx path from the photodetector directly to an analog-to-digital converter (ADC) or a time-to-digital converter (TDC). The LMG1025 is a discrete laser driver that drives an external gallium nitride field-effect transistor (FET) capable of producing 1.25nS pulses. TI’s integrated LMH13000 laser driver does not require an external FET and can drive lasers with adjustable current from 50mA up to 5A, creating pulses <1nS. The LMH13000 is also approximately four times smaller than discrete laser driver solutions. Using multiple LMH13000 devices in parallel can increase the amount of current going to the laser.

TI’s receive path amplifiers include the LMH32401 and LMH32404 for ADC-based systems and the LMH34400 for TDC-based systems. These devices are beneficial to lidar applications because they integrate a high-speed transimpedance amplifier (TIA) compensation network, and include features such as ambient light cancellation, input overcurrent clamp protection and a multiplexer mode.

The ambient light cancellation circuit enables better detection of the input current by removing DC ambient light signals, and saves board space because you can use this circuit instead of AC coupling between the photodiode and amplifier. The input overcurrent protection clamp absorbs and diverts excess current to the positive supply when the amplifier detects its nodes, entering a saturated condition that allows the amplifier to return to a linear state much faster and limiting pulse extension to less than a few nanoseconds. The integrated lidar TIAs have integrated output switches that enable the connection of multiple photodiode and amplifier channels to fewer ADC and TDC channels, and thus eliminate the need for a discrete multiplexer. This makes it possible to use multiple sensors while saving board space that would ordinarily be taken by multiple ADC and TDC channels.