Current monitoring for the PCO-7110, PCO-7111, and PCO-7114
There's an easy way to see an accurate rendition of the output pulse from a PCO-7110, PCO-7111, and PCO-7114 on your oscilloscope.
These modules include a circuit that works with the optional PCA-9140 current monitor cable. The scale factor is 20 A per V into 50 Ω, which means the input impedance of the scope should be set to 50 Ω (or a 50 Ω terminator should be used). The displayed waveform is scaled to 1 V of amplitude for every 20 A of output current.
How does it work? The driver contains a very low value of resistance in series with the output that converts the laser diode current to a small voltage. The cable contains a 50 Ω series resistor that creates a 50% voltage divider in combination with the 50 Ω scope input impedance. (The scale factor takes this divider into account.)
Compared with a standard scope probe, you'll see much less noise with this low-impedance system. The combination of a standard probe's long ground lead and the scope's high input impedance results in significant noise pickup from the high currents being switched nearby.