SLYT876 April   2026 LMH13000

 

  1.   1
  2. 1 Introduction
  3. 2 What makes laser pulse control challenging?
  4. 3 Effects of rise and fall times
  5. 4 Propagation delay
  6. 5 Pulse-to-pulse stability
  7. 6 Implementing precise laser pulse control
  8. 7 Precise pulse control in pulsed systems
  9. 8 Practical example with transmitter test results
  10. 9 Conclusion
  11. 10Additional resources
  12. 11About the authors

3 Effects of rise and fall times

Lidar and ToF systems measure the distance by calculating the round-trip time for a laser pulse to travel to a target and return to a receiver. The ability to distinguish small distance changes depends on how quickly the pulse edges transition between no light and full light. Faster rise and fall times reduce distance uncertainty and give the receiver a clearer reference point. In high-resolution systems, rise and fall times typically range from 1ns to 5ns.

When a pulse edge is slow, the system cannot determine the exact moment the signal crosses the receiver detection threshold. A tr/f equal to a 1ns edge therefore introduces about 150mm of distance uncertainty, approximated by Equation 1:

Equation 1. ∆ D = c t r / f 2

where ΔD is the delta distance and c ≈ 3 × 108m/s.

This uncertainty increases with slower pulse edges, which parasitics such as package and printed circuit board (PCB) inductance can limit, along with the capacitance of the laser diode and driver output. For example, increasing tr/f from 500ps to 1ns doubles the distance, while edges of 2ns expand it to nearly 300mm, limiting the system's ability to distinguish smaller differences in target distance then ΔD.