A Tunable Non-Foster T-Network Loaded Transmission Line Using Distributed Amplifier-Based Reconfigurable Negative Group Delay Circuit

A novel tunable non-Foster T-network loaded with transmission lines (TLs) using a two-stage distributed amplifier (DA)-based negative group delay (NGD) circuit is proposed. The tunability comes from the NGD response synthesized by adjusting the ratio of the transconductance of the transistors, and the varactors at both the input and output port. Due to the distributed topology, the proposed T-network not only works within a relatively broad band (several hundreds of Mega-Hertz), but also has good input and output matching characteristics. A prototype of the proposed non-Forster T-network is built and tested. By properly amending the in-band magnitude and phase characteristics, the NGD circuit can realize the targeted non-Foster T-network with unconditional stability. The experimental results show that the tunable equivalent T-network has a 0 pF to - 1.5 pF shunt capacitance and a 0 nH to -1.875 nH inductance.