Highly Power-Efficient Active-RC Filters With Wide Bandwidth-Range Using Low-Gain Push-Pull Opamps

This paper presents a generic-purpose solution of highly power-efficient active-RC filters, which is suitable for analog baseband with wide bandwidth-range from several mega-Hz to hundreds of mega-Hz in wireless receivers. A 260 μA 7-20 MHz 6th-order active-RC low-bandwidth low-pass filter (LBW-LPF) and a 2.3 mA 240-500 MHz 6th-order active-RC high-bandwidth low-pass filter (HBW-LPF) are implemented in a standard 0.18 μm CMOS process to demonstrate this versatile solution. Highly power-efficient push-pull opamps with 30-to-35 dB gain are adopted for the filters, which allow us to focus on extending the bandwidth and reducing the power consumption. The push-pull opamp with adaptive-biased and pole-cancellation push-pull source follower (APP-SF) as the buffer stage is proposed to greatly reduce the power consumption and effectively extend the bandwidth. An adaptive bias mechanism is also proposed to tolerate the PVT variations for the opamps. In addition, the GBW compensation and the Q-degrading scheme are adopted to relax the opamp GBW requirement, further reducing the power dissipation. The LBW-LPF only consumes 260 μA current from 1.8 V supply, achieves 14.4 dBm in-band IIP3 and 66.2 nV/√ Hz IRN density, and occupies 0.21 mm ² silicon area without pads. The HBW-LPF merely dissipates 2.3 mA current from 1.8 V supply, achieves 11.3 dBm in-band IIP3 and 13.1 nV/√ Hz IRN density, and occupies 0.23 mm ² silicon area without pads.