Scalable, low-power and high-performance active-RC complex band-pass/low-pass filter with automatic frequency tuning applied to the Internet of Things

Abstract

This article introduces a comprehensive 3rd Chebyshev active-RC complex band-pass/low-pass filter with an automatic cut-off frequency tuning circuit. The designed filter achieves 2 dB step gain control within the range of −6 dB–24 dB and 4 different bandwidth modes including low-pass modes and complex band-pass modes. A compact fully-differential (FD) amplifier with feedforward compensation and reverse pole splitting technique is used to meet the stringent filter's performance. The novel amplifier achieves an open loop gain of 62 dB and a maximum unity-gain bandwidth (UGB) of 732 MHz with VDD = 0.9 V and 0.32 mW of power dissipation. Using the proposed amplifier, the filter achieves the lowest power consumption reported in the literature for active-RC implementations and 30 % power reduction over similar active-RC filters. By employing an optimized solution for dynamic allocation of inter-stage gain, the filter achieves a maximum in-band-IIP3 of +25.7 dBm and an improvement of 2 dB. Also, an automatic frequency tuning scheme is used to eliminate the effect of process variation. The filter is fabricated in 22 nm CMOS process occupying 0.44 mm $\times$ 0.44 mm area and consuming 1.8 mW and 1.2 mW from 0.9 V supply voltage in Wi-Fi and BLE modes, respectively. The maximum figure of merit (FoM) is 142.6 dB/J. The RC tuning circuit has a precision of 1.5 % and covers a range of 20 %.