Hamidreza Ghanbari Khorram - Department of Electrical Engineering, Hamedan University of Technology, Hamedan ۶۵۱۵۵, Iran
Alireza Kokabi - Department of Electrical Engineering, Hamedan University of Technology, Hamedan ۶۵۱۵۵, Iran

Using Nested Cross-coupled positive resistive feedback along with the positive capacitive feedback, a novelGain×Bandwidth expansion technique is proposed for cascade amplifiers. The proposed method enhances the overallamplification at high frequencies for the cascade structures of a common base and common collector stages. Having thefixed capacitive circuit elements, the method also provides a tuning resistive parameter to adjust the desired values forthe bandwidth, input impedance and the feedback ratio. An AC model of the proposed topology is also presented here todeliver the better understanding of the proposed method along with the behavioral comparison with the previous PCFbasedamplifiers. Furthermore, the exact pole-zero analysis shows the better stability of the presented topology for thewider range of the source impedances. The 300GHz-fT SiGe technology has been considered here and it is shown that abandwidth in the order of 145GHz at the voltage gain of 24dB is achievable when a 150 Ω source resistance is used.Therefore, the proposed three-stage cascade amplifier can deliver a bandwidth which is 48% of its transistors transitionfrequency.

Wideband Amplifier, Nested Feedback Topology, Positive Capacitive Feedback (PCF)