A Novel Fully Reconfigurable Non Foster Capacitance Using Distributed Negative Group Delay Networks

A novel reconfigurable non-Foster capacitance (NFC) using negative group delay (NGD) circuit is presented in this paper. The NGD circuit is based on a multi-order distributed amplifier which is used to achieve both NGD performance and gain compensation. By introducing shunt and series varactors next to trans-conductance transistors in the amplifier, the characteristic impedance, and electric length of transmission lines in the distributed amplifier can be flexibly tuned. As a result, the gain, phase shift, and negative group delay value of the proposed NGD circuit can be easily controlled as desired, and therefore, the scattering parameters S
₂₁
can be adjusted to match with an ideal NFC, resulting in reconfigurable non-Foster capacitance. The working frequency ranges, equivalent negative capacitance value, and connection modes of the NFC be fully reconfigured by appropriately controlling the voltages applied to the varactors. Both simulation and measurement results were given, which agree well with each other. The experimental results show that the NFC value can be tuned from -1.1 to -2.5pF with 1 GHz center frequency and the working frequency can be tuned from 0.7 to 0.8 GHz with -10 pF shunt NFC.