A Tx RF 0.1dB IL bandpass filter for fully digital cellular transmitters in 65-nm CMOS

In this paper, we present a bandpass filter designed and implemented in 65-nm CMOS. From 0.8-2.2GHz filtering requirements are very challenging. This filter is dedicated to fully digital RF Tx cellular architectures, and is available for any Tx architecture. Our filter uses highly linear CMOS active inductors that exhibit Q factors above 1000 at cellular frequencies to reduce filter insertion losses. The highly linear characteristic of implemented active inductors drive it us to 0dBm operation while providing at least 24dB attenuation at ± 400MHz from F₀. Measurement results of the filter show a central frequency (F0) of 1.8GHz with 135MHz of -3dB bandwidth (BW) with less than 0.1dB IL.