An Ultra-Low Power Bandpass Filter Bank with Input and Output Common-Mode Feedback in FD-SOI

To implement frequency sensitivity in always-on audio-frontends that predominantly utilize analog signal processing techniques, banks of bandpass filters are needed. Due to their deployment in low-voltage environments, keeping all transistors in saturation under all conditions poses a challenge. We propose a common-mode feedback concept for flipped voltage follower based bandpass filters making use of the backgate terminal in SOI technologies. It sets the operating points of the filter core, ensuring proper functionality under all process variations and a temperature range from -20°C to 85° C. We conducted a comprehensive mathematical analysis, deriving design guidelines for the common-mode feedback loops. The bandpass filter bank with the proposed common-mode feedback concept has been simulated and verified on schematic-level achieving a total power consumption of 64.3 nW and a DR of approximately 50 dB while covering a frequency range from 44 Hz to 7.8 kHz.