A Configurable Active Bandpass Filter with DC Offset Suppression for Direct Down-Conversion Wake-Up Receivers in 28 nm

Abstract

This paper presents the design of an integrated active band-pass filter for 1ow-IF or direct down-conversion wake-up receivers suited for IEEE 802.11ba. Two gyrator-based second-order gm-C structures are used to achieve an overall low-pass filtering order of at least 4. Fully differential operational transconductance amplifiers (OTA) with capacitive source degeneration and capacitive load result in a band-pass frequency response. This way, the down-converted signal is filtered and DC offsets from previous stages are suppressed. By adding two programmable gain amplifiers (PGA) that show first-order low-pass behavior as well, the whole structure also acts as a gain stage and the filtering is slightly improved. The band-pass filters and PGAs are arranged in an alternating fashion in order to prevent possible DC offsets from propagating through the chain. Every stage features a common-mode feedback (CMFB) loop. The nominal filter bandwidth is from 150kHz to 2MHz and the upper band edge can be varied between 1.5 MHz and 4. 5MHz. The overall gain is adjustable between 0dB and 42dB and the whole structure only needs 25 $\mu$A at 900mV supply voltage. The filter is implemented in a 28nm CMOS technology. The design was verified by post-layout simulations.