NIC-based capacitance multipliers for low-frequency integrated active filter applications

In this paper we present fully integrable, grounded and floating, positive and negative capacitance multipliers, all designed starting from the well-known Negative Impedance Converter (NIC) circuit, implemented through operational amplifiers (Op-Amp). The proposed topologies are very simple and employ a reduced number of active elements. Negative and positive capacitance behaviour can be simulated for a large frequency range depending on the active component performance in terms of DC gain and band-width. The sign can be regulated either by cascading two or more stages of the same simulator or introducing a further NIC circuit, replacing an appropriate resistor into the scheme. Theoretical formulations are addressed and compared with PSpice simulation results, showing their complete agreement. Since high values of capacitance can be easily obtained, the proposed circuit is suitable for low-frequency integrated low-pass active filter implementation where tunability is also easily allowed by varying only a resistance value.