Imaging LiDAR systems such as Goddard’s Reconfigurable Solid-state LiDAR (GRSSLi) must collect and process reflected pulses of light in order to correctly assemble a three-dimensional image of the scene. These pulses of light generally range from 2-5 nanoseconds in duration. Consequently, to collect a large number of samples for this short pulse, a high-sample-rate analog to digital converter (ADC) must be used. Other methods such as threshold detection could be used, but generally these detection methods suffer degradation in overall range, measurement accuracy, and precision due to the random nature of return pulse intensity. In addition, scientifically valuable information can be gleaned from the shape of the returned waveform.
Once the high-rate ADC captures all the samples of the reflected laser waveform, the samples must be processed so time-of-flight of the laser light can be accurately measured to determine the range. These requirements, coupled with the need to operate a modular cPCI-based system, support the implementation of onboard machine vision algorithms, and a desire to keep development costs low drove the LiDAR designer to incorporate a high-speed ADC chip with an existing reconfigurable FPGA-based rad-hard spaceflight processor design called SpaceCube 2.
The innovation described here combines a 2-channel, 1.6-gigasample-per second, 12-bit ADC with high-performance reconfigurable computing into a modular, low-power, high-reliability spaceflight electronics card design.
A full electronics board has been designed, fabricated, and tested. The design includes:
- 2x Xilinx Virtex-5 FX130T FPGAs, back-to-back (one will be the main controller)
- 1x Aeroflex CCGA FPGA, Xilinx initial configuration, watchdog, system timer, debug
- 1x 64-Mb PROM; contains initial Xilinx bitfile
- 1x 16-MB SRAM, rad-hard with auto EDAC/scrub feature
- 32-bit data bus, ~20ns read/write operations
- SEL monitor circuit
- JTAG scheme
- 16-channel analog/digital circuit for general board health, ~6 external channels
This work was done by Nathaniel Gill, Robert Moss, and David Petrick of Goddard Space Flight Center. GSC-17227-1