$$\pm \, 0.5$$ V, 254 $$\upmu $$W Second-Order Tunable Biquad Low-Pass Filter with 7.3 fJ FOM Using a Novel Low-Voltage Fully Balanced Current-Mode Circuit

A high-performance CMOS, fully balanced second-generation current conveyor (FBCCII) is proposed to exclusively use CCII circuits in integrated circuit applications. In the proposed circuit, a current folding technique is applied to a fully balanced version of transconductance amplifier. The proposed FBCCII consumes 84 $$\upmu $$ W of power and has an open-loop gain of 47.83 dB with 62.9 $$^\circ $$ of phase margin. The simulated input referred noise is 155 nV/ $$\sqrt{\text {Hz}}$$ @ 1 KHz and has a unity gain bandwidth of 39.8 MHz. A common mode feedback (CMFB) circuit is also proposed to improve the dynamic range of the proposed FBCCII circuit by 50 $$\%$$ as compared to the circuit with-out CMFB. The CMFB consumes 170 $$\upmu $$ W of power and has a bandwidth of 60 MHz. The proposed circuit is simulated using standard 180 nm CMOS process operating at $$\pm \,0.5$$ V supply voltage. To verify the effectiveness of the approach, a fully differential variable gain amplifier with tunable gain from 0 to 30 dB is designed. Also, a bandpass filter with quality factor = 4 and bandwidth of 10 MHz is designed using the proposed FBCCII. A novel low-pass filter (LPF) using the proposed FBCCII is designed for bio-medical applications. The proposed LPF is a second-order filter with the cut-off frequency of 55 Hz and 121 nV/ $$\sqrt{\text {Hz}}$$ of input-referred noise. The LPF is designed at a supply voltage of $$\pm \, 0.5$$ V, and the spurious free dynamic range of proposed LPF is 85 dB. The figure of merit of the LPF is 7.3 fJ. The layout area of the proposed FBCCII design is 6889 $$\upmu $$ m $${^2}$$ ( $$83\,\upmu \text {m} \times 83\,\upmu \text {m}$$ ).