Abstract
Timing walk error in pulsed time-of-flight based laser range finding was studied using two different types of laser diode drivers. The study compares avalanche bipolar junction transistor (BJT) and metal-oxide-semiconductor field-effect transistor switch based laser pulse drivers, both producing 1.35 ns current pulse length (full width at half maximum), and investigates how the slowly rising part of the current pulse of the avalanche BJT based driver affects the leading edge timing walk. The walk error was measured to be very similar with both drivers within an input signal dynamic range of 1:10 000 (receiver bandwidth of 700 MHz) but increased rapidly with the avalanche BJT based driver at higher values of dynamic range. The slowly rising part does not exist in the current pulse produced by the metal-oxide-semiconductor (MOS) based laser driver, and thus the MOS based driver can be utilized in a wider dynamic range.
Highlights
The pulsed time-of-flight (TOF) laser range finding techniques operate by sending a short laser pulse to the target and measuring the time interval between the submitted pulse and the reflected echo
With laser pulses ∼3 ns [full width at half maximum (FWHM)] in length, a receiver bandwidth of ∼200 MHz is used, and the corresponding timing walk is ∼2 ns in a dynamic range of 1:100 000.6 Many different techniques have been suggested to minimize the timing walk, e.g., the measurement of the pulse width and/or rise time or the pulse amplitude and using this information for timing walk error compensation based on prior calibration
We have compared the drive currents and optical output pulse shapes of avalanche bipolar junction transistor (BJT) switch and metal-oxide-semiconductor field-effect transistor (MOSFET) switch based laser diode drivers working in the LCR transient mode
Summary
The pulsed time-of-flight (TOF) laser range finding techniques operate by sending a short laser pulse to the target and measuring the time interval between the submitted pulse and the reflected echo (see Fig. 1). With laser pulses ∼3 ns [full width at half maximum (FWHM)] in length, a receiver bandwidth of ∼200 MHz is used, and the corresponding timing walk is ∼2 ns in a dynamic range of 1:100 000.6 Many different techniques have been suggested to minimize the timing walk, e.g., the measurement of the pulse width and/or rise time or the pulse amplitude and using this information for timing walk error compensation based on prior calibration. It is shown that an avalanche driver, which is typically used for high-speed/high-power driving of semiconductor laser diodes, introduces a relatively slowly rising current component to the high-speed switching current This component slows down the edge speed of the optical output from the laser diode with the result of increased timing walk, especially for very large echoes for which the timing threshold is at the root of rising the optical pulse. A metal-oxide-semiconductor (MOS) based driver does not produce this slow component, and the total timing walk is lower
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