FINAL STAGE OF AN OPTICAL TRANSMITTER FOR DIGITAL SIGNAL TRANSMISSION

摘要

In the final stage of an optical transmitter for digital signal transmission there is a shunt transistor (Ts) in a common emitter circuit in parallel with the transmitter diode (D), and between its input and output a negative feedback network is connected. To avoid any unwanted storage effect because of saturation of the shunt transistor (Ts) irrespective of its collector current, the negative feedback network is designed so that a reduction in the collector potential of the shunt transistor (Ts) below a value, which can be set and which lies above its saturation voltage, is prevented by a reduction in its base current. A particularly useful form of this negative feedback network as a current source consists of a transistor (Tg), the base of which is connected to an adjustable voltage source (URef) and which is connected on the emitter side via a resistor (RG) to the collector of the shunt transistor (TS) and on the collector side to the non-inverting input of a preamplifier (Tv, R1, R2, R3, R4), the output of which is taken to the input of the shunt transistor (Ts).