A Tunable Series Negative Capacitor Using Distributed Amplifier-Based Reconfigurable Negative Group Delay Circuit

A novel tunable non-Foster negative capacitor with unconditional stability using a two-stage microwave distributed amplifier (DA) based negative group delay (NGD) is presented. The tuning mechanism is realized by changing both the transistor's transconductance and input/output phase responses. To achieve this, the transistors placed at each stage of the DA are tuned separately, and two identical varactors placed at the input port and output port are tuned by one single voltage. As proof-of-concept, a prototype of the proposed DA-NGD circuit based tunable negative capacitor is built and tested. The measurement results show that, the negative capacitor can be successfully tuned between -0.5 pF to -1.0 pF.