Light emitter with laser diode control - uses detector output signal and has circuit providing output and bias control signals for diode

摘要

From the output of a detector comprising a photodiode (1) and a wide-band amplifier (2) are derived a first signal (P1), corresponding to the level of maximum modulation, and a second signal (P0), corresponding to the minimum level of modulation. The second signal (P0) is subtracted from the first signal (P1) in a differential amplifier (9). The output (PM) represents the value of modulation. This output (PM) is fed to one input of a comparator (10), and a modulation reference signal (PMref) is fed to another input. The output of the comparator (10) is used to keep the laser to its predetermined output. The second signal (P0) is also compared in a second comparator (11), with a reference threshold value (P0 ref) representing the required emission threshold. The output of the second comparator (11) is a threshold error signal which is used to adjust the bias voltage of the laser diode.