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Non- Foster Networks for Tunable and Wideband RF Devices


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As a short summary, the realized outcomes of the project are: We have shown that all electronic circuits that mimic negative immittance (NICs and NIIs) rely on the superposition of the original signal and assisting signal. Since these signals must be coherent, all classical circuits use positive feedback, which often leads to instability. It is extremely important to make a clear distinction between electronic admittance (associated with SCS properties) and electronic impedance (associated with OCS properties). We have also shown that a simple one-pole model of the NIC/NII amplifier is a useful approximation for both prediction of dispersion properties for frequencies below the pole frequency and for stability predictions. It was found that the dispersion of all the circuits analyzed is negligible when the maximum operating frequency is below one-tenth of the frequency of the first pole. The "parasitic" real part of the input impedance/admittance of the negative capacitor/inductor is negative in the SCS design and positive in the OCS design. This "parasitic" conductance/resistance can be compensated by an additional passive load network. We have reviewed all known methods of stability prediction and proposed a simple, straightforward method to develop simple equivalent circuits for all one-pole non-Foster and negative elements. We have also studied the most common realizations of NIC/NII circuits and performed a very thorough analysis of their stability properties. As expected, the stability properties were found to depend on both the NIC/NII topology and the passive external network topology. It was found that both OCS and SCS DC coupled negative capacitors/inductors/resistors based on NICs or NIIs always have an unstable DC pole that degrades the stability robustness. In addition, the DC coupled negative OCS capacitor and negative SCS inductor have a pole at the origin that causes DC offset at the input. The overall conclusion is that there is no such thing



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