Why is does the current deviate from my set current after a calibration with a PLCS-21 and a compatible LDP-V driver?

The calibration process is carried out by ramping up the high voltage (HV) from the user definied minimum value to the maximum value. This is done by sending out a pulse with 50 ns pulse duration and varying the HV voltage between each pulse. At each data point the corresponding current value is measured and stored in the database.

Thus, it is very important how the rise time of the current signal is. If the rise time exceeds the pulse duration at a given current, the full current is not achieved anymore. This can lead to deviations between the set current and the real current if either the 50 ns measurement pulse or the later used pulse duration is below the rise time threshold. This usually happens if the impedance of the laser diode and its connections is too high. For more information please refer to the application notes “LD Connections” and “Impedance of Laser Diodes”.