DC–coupled broadband and gain controllable monolithic amplifier circuits

Abstract

AbstractThis paper will describe a method for broadening the bandwidth of gain controllable monolithic amplifier circuits for the purpose of the application to the repeater circuits in the Gb/s optical transmission systems. The gain controllable differential amplifier circuit exhibits narrower bandwidth because of larger parasitic capacitance components in comparison with basic differential amplifier circuits due to the complicated circuit configuration to control the gain. Also, when the peaking method for broadening the bandwidth is applied, the peaking amounts exceed the optimum value and becomes unstable in the low‐gain operation even if the peaking amounts are optimized for the high‐gain operations. In this paper, a new gain controllable amplifier circuit using the bias current dependency of differential resistance of diodes is proposed. Furthermore, the circuit is fabricated by using the Si Bipolar Super Self‐Aligned process Technology (SST). A broadband characteristic of 1.6 GHz bandwidth and 29‐dB gain controllable width has been obtained. These are sufficient for the application to the Gb/s optical repeater circuits.