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An 1.1 V 0.1–1.6 GHz tunable-bandwidth elliptic filter with 6 dB linearity improvement by precise zero location control in 40 nm CMOS technology for 5G applications

A linearity improvement technique for elliptic filters in low-supply-voltage transceiver design for 5G (5th generation of mobile technology) communication systems has been proposed. The zero in the transfer function has been placed at the third-harmonic of the intermediate frequency (IF) signals in order to suppress the undesirable components, and thus the total harmonic distortion (THD) can be dramatically reduced. To achieve precise zero control to maximize linearity optimization, the transfer function of the elliptic filter with Tow-Thomas-II implementation has been re-derived, taking into account the operational amplifiers (op-amps) nonidealities. In this paper, a fourth-order low-pass filter, composed of two cascaded Tow-Thomas-II biquads, has been described and simulated to validate the linearity improvement technique, which features a 0.1–1.6 GHz tunable 3-dB bandwidth. In addition, 6 dB THD enhancement can be realized when adopting modified transfer function, and THD can be smaller than −46 dB with −1 dBm input power, corresponding to 1.2 Vpp differential output signal.