A BiCMOS Laser Control Chip Combining Power Control and 622MBit/s Modulator

This paper presents a circuit to control laser diodes implementing modulator and power control circuits on the same chip. The modulator is an ECL-input compatible modulator designed to work with data rates of more than 622MBitls. The modulator´s output current is variable up to 40mApp. The power control regulator has a closed loop bandwidth of less than 100Hz. The regulator is implemented using a voltage integrator followed by an output stage capable of supplying a laser diode current of up to 120mA. The regulator combines a current division technique employing MOS transistors with a current conveyor based time constant enhancement technique. The output stage that supplies the laser diode´s current includes a high input to output ratio current mirror implemented using an area efficient topology. Simulations indicate that the presented current division technique and time constant enhancement technique should be viable to implement even larger time constants than the one presented in this paper. The chip is fabricated in a 2¿m BiCMOS process.