DC-coupled IF stage design for a 900-MHz ISM receiver

This paper presents a dc-coupled 900-MHz ISM band RF front-end for a short-range wireless receiver. The front-end, fabricated in a 0.5-μm CMOS process, is intended as a test vehicle to verify the proposed dc-coupled topology. In this topology, a low-frequency feedback circuit suppresses the dc offset and low-frequency noise at the mixer output. The dc-coupled topology is compared with traditional ac coupling. We show that there is a tradeoff between bandwidth and midband loss in a fully integrated ac-coupled system. The proposed dc-coupling technique does not impose this tradeoff. The dc-coupled topology was verified via simulation and measurements from the test vehicle.