Optimum emitter aspect ratio for bipolar fiber-optic preamplifiers

Many monolithic fiber-optic preamplifiers use a bipolar transistor as the front-end device due to process restraints, despite the relatively poor noise performance of the bipolar transistor. This paper shows that there is an optimum emitter aspect ratio in a bipolar transistor operated at the optimum collector current for noise performance. An expression for this optimum emitter aspect ratio is developed and shown to agree very well with simulation results.