Performance analysis of SiGe-HBT-based transimpedance amplifiers with nonconstant gain-bandwidth technique

The performance of a transimpedance amplifier (TIA) can be enhanced by lowering the input impedance and applying the nonconstant gain-bandwidth product (GBP) technique. In this paper, a TIA of utilizing both properties is presented and the performance of the conventional and the proposed TIAs is analyzed theoretically and experimentally. The lowered input impedance increases the operational bandwidth whereas the nonconstant GBP decouples the tradeoff relation between the gain and the bandwidth of the conventional TIA. Since this advantage of the enhanced performance is achieved at the cost of degradation in noise characteristics, however, comprehensive noise analysis and in-depth comparison between the conventional and the proposed TIAs are investigated. In the proposed design, a common-base stage is inserted as the first stage in the conventional TIA for lowering the input impedance. In addition, the global feedback network is formed for achieving nonconstant gain-bandwidth. Compared with the conventional TIA, the measurement results show that the proposed TIA presents a 6.3× increase in GBP and a 33% increase in the spot noise, exhibiting an improvement of 3.5× in the overall figure-of-merit.