A 1V current-mode filter in 65nm CMOS using capacitance multiplication

A new capacitance saving method for differential current-mode filter structures is presented. Especially filters with low cut-off frequencies need large capacitors, which comes along with large and expensive chip area. We show the opportunity to save chip-area in a 3rd-order current-mode Butterworth low-pass filter and enlarge the effective capacitance value by 30%. The proposed filter is designed to be in a transmit path in a software defined radio of a mixed-signal system on chip. It is developed and fabricated in low-power 65 nm CMOS and needs an active area of 215 mum times 215 mum. The supply voltage is 1 V at a current consumption of 9.6 mA. The filter reaches a third-order input intercept point of 1.6 mAp and a dynamic range of 73.8 dB at a cut-off frequency of 1 MHz.