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The laser board generates the optical pulses with a wavelength of 905nm. It uses four Osram SPL LL90_3 Radial Smart Lasers. All lasers are driven simultaneously for an increase in beam strength giving longer range. A PWM signal generated by the FPGA carrier board with programmable pulse width and frequency is used to control the lasers. The signal is generated on the FPGA as LVDS to make it less susceptible to noise as it travels from the FPGA to the Laser board through the DAQ board and the ribbon cable connecting the DAQ and the Laser boards. It is converted on the Laser board to single ended mode using the ADN4691E, an M-LVDS transceiver. The single-ended signal is then fed to the ADP3634, a high current and dual high-speed driver. Each output can source up to 4A and the typical rise and fall times are 10ns at a 2.2nF load. The design of the Laser board PCB was done is such a way that the trace loop of the drive signal as well as that of the LED power currents were minimized in order to reduce their parasitic inductance and maintain the desired high current slope dI/dt.
The drive signal can be fed back to the ADC for time of flight reference. However, it is single ended and must be converted to differential form. Thus, an ADA4930-1 is used, a very low noise, low distortion, high speed differential amplifier. The common mode voltage is set similarly to that of the ADA4950 on the TIA board.
An external power supply is used to power the lasers. The kit comes with a 12V @ 4A supply. For safety reasons the power to the lasers is turned only only by pressing the S1 switch.