How does the operating bandwidth of non-foster negative capacitor affect its stability properties?

Abstract

The comparative analysis of the stability properties of three generic types of negative non-Foster capacitors (ideal non-dispersive type, low-pass type, and band-pass type) is presented. It is shown that the range of external RC loads that ensure stable operation for a band-pass negative capacitor significantly exceeds the ranges required for both a low-pass negative capacitor and an ideal dispersionless negative capacitor. Furthermore, the rigorous inequality is derived, which connects the operating bandwidth and a range of permissible external loads, thus enabling a straightforward design of practical stable non-Foster systems. Finally, the RF hardware demonstrator (100 kHz–100 MHz) of the band-pass negative capacitor was fabricated, and all measurement results were found to be in very good agreement with the theoretical predictions.