A laser control chip combining a power regulator and a 622-Mbit/s modulator

This paper presents a circuit combining a 622-Mbit/s laser diode modulator and a power regulator with a closed loop bandwidth of less than 100 Hz. The power regulator´s closed loop bandwidth is implemented using an integrator configuration employing a current division technique to implement a large integration resistor, and an electronic time-constant enhancement technique to achieve the desired closed loop bandwidth. Impacts of the electronic time-constant enhancement technique on noise performance are discussed. The power regulator includes an output stage capable of delivering the needed bias current for the laser diode. The output stage is implemented as a high-ratio bipolar current mirror using an area-efficient topology. The modulator has ECL-compatible inputs including 50-Ω input termination resistors, and it can modulate the laser diode with a current of up to 45 mA_pp