On frequency response and stability of an optical front–end with variable‐gain current amplifier using a bipolar junction transistor translinear loop

A comparative analysis of implementations of an optical front–end with variable transimpedance intended for optical storage systems in two different BiCMOS technologies is given in this article. The variable-gain current amplifier within the optical front–end is designed by using a modified balanced type of the bipolar junction transistors translinear loop. The predictions of the optical front–end mathematical models are confirmed by the measured results. They show that a 0.6-µm BiCMOS silicon technology implementation with worse bipolar junction transistor parameters (unity-gain frequency, current gain β, and the Early voltage) gives much better stability than a 0.35-µm BiCMOS silicon-germanium technology implementation. As a consequence, the useful measured transimpedance dynamic range of the proposed optical front–end is 17.5 times larger in the 0.6-µm BiCMOS silicon technology than that in the 0.35-µm BiCMOS silicon-germanium technology. Copyright © 2012 John Wiley & Sons, Ltd.