Question

Compute the rise time of a photo detector if its 3-dB bandwidth is 250 MHz.

Answer 1

Rise Time is the time required for the photodetector output level to change from 10% to 90% of the peak output level.

The frequency at which the detector output power decreases by 3dB from the output at 100kHz is called cutoff frequency.

Bandwidth: The difference between the high and low cutoff frequencies, measured in Hertz. The bandwidth of the photodetector is approximately related to the rise time (Tr) by:

           Bandwidth (Hz) ≈ 0.35/Tr

Therefore, rise time, Tr = 0.35/250MHz = 1.4 ns