A new ultra-low power wide tunable capacitance multiplier circuit in subthreshold region for biomedical applications

Implementing large capacitors in integrated circuits demands an occupation of a relatively significant large silicon area on-chip, which strictly limits the capability of the physical implementation of low-frequency integrated circuits that mostly require high capacitance values to provide large time-constants. Capacitance multipliers have been proposed to overcome this issue to realize high-value active capacitances in a small chip area. This paper proposes a new current-mode ultra-low power capacitance multiplier based on the floating capacitance Super Flipped Current Follower (SFCF) circuit which employs two AB class cascaded stages. The main novel idea behind the proposed circuit is combining the cross-coupling Quasi-Floating Gate (QFG) with the classAB techniques and employing the Super Flipped Current Follower (SFCF) circuit, to enhance the adjustment efficiency ratio (M) factor, while also achieving a high scaling factor "K". As a result, the proposed circuit achieves higher K value at the lower power and chip size area costs, while providing better adjustment efficiency ratio (M), which realizes a better "capacitance adjustability-power" trade-off. The proposed circuit provides other advantages such as: wide electronic tunability of scaling factor K, large Parallel Load Resistance (PLR) value, small value of Equivalent Series Resistance (ESR), relatively small chip size area, and a high ratio of adjustment efficiency (M). The total power consumption of the proposed circuit is obtained as 101 nW, using a base capacitance (Cb) of 1 pF, which leads to the realization of a maximum achievable equivalent capacitance (Ceq) of 1604 pF. In addition, the performance of the proposed tunable capacitance multiplier is examined in the realization of a wide-tunable low-pass filter structure. Furthermore, the performance robustness of the proposed circuit is investigated by the Monte-Carlo and PVT analyses in different technology corners, which justify the good performance of the proposed circuit that makes it a proper candidate to be used in ultra-low power biomedical signal processing.