Theoretical study on stable broadband non-Foster negative capacitors yielded by parasitic reactance of an operational amplifier

This paper proposes a new method to design negative capacitors by utilizing a parasitic reactance of an operational amplifier. Different from the conventional ways to use negative impedance converters (NICs), the proposed circuit does not include any impedance elements whose sign is to be reversed by the NIC topology. Therefore, the yielded negative capacitance cannot be tuned flexibly. However, the proposed method can provide a stable broadband negative capacitance. From the circuit simulation, a negative capacitance from -304pF to -275pF (5% criteria for -290pF at 89MHz) is yielded in a frequency range from 37MHz to 100MHz with a reflection coefficient from -4.5dB to -2.1dB.