A Wideband Inductorless CMOS Front-End for Software Defined Radio Receivers

The number of wireless communication links is witnessing tremendous growth and new standards are being introduced at high pace. These standards heavily rely on digital signal processing, making CMOS the first technology of choice. However, RF CMOS circuit development is costly and time consuming due to mask costs and design iterations. This pleads for a Software Defined Radio approach, in which one piece of flexible radio hardware is re-used for different applications and standards, downloadable and under software control. To the best of our knowledge, little work has been done in this field based on CMOS technology. Recently, a bipolar downconverter front-end has been proposed [1]. In CMOS, only wideband low-noise amplifiers have been proposed, and some CMOS tuner ICs for satellite reception (which have less stringent noise requirements because they are preceded by an outdoor low-noise converter). This paper presents a wideband RF downconverter frontend in 0.18 um CMOS (also published in [2]), designed in the context of a research project exploring the feasibility of software defined radio, using a combined Bluetooth/WLAN receiver as a vehicle. Usually, RF receivers are optimised for low power consumption. In contrast, we have taken the approach to optimise for flexibility. The paper discusses the main system and circuit design choices, and assesses the achievable performance via measurements on a front-end implemented in 0.18um CMOS. The flexible design achieves a 0.2-2.2 GHz -3 dB bandwidth, a gain of 25 dB with 6 dB noise figure and +1 dBm IIP3.