Stability conditions for a digital discrete-time non-Foster circuit element

Digital discrete-time implementations of non-Foster circuit elements offer an alternative to conventional analog circuit approaches. In particular, the design of a discrete-time negative capacitor is investigated, since such non-Foster circuit elements offer significant potential in wideband antenna, metamaterial, and artificial magnetic conductor applications. As with analog non-Foster circuits, stability is an important design consideration for digital non-Foster elements. Therefore, stability conditions and simulation results are presented for a discrete-time negative capacitor, and the onset of instability is shown near the predicted stability boundary.