Design of 2~2.5 GHz variable gain LNA and 2.4 GHz low power folded RF front-end

Abstract

Currently, there are two demands in RF front-end design such as multi-standard application and low power consumption. However, it is difficult to satisfy these demands simultaneously. Therefore, two design techniques are explained in this paper, respectively. In this paper, two RF circuits, a variable gain LNA and low power folded RF frontend, are designed. At first, a variable gain LNA (VG-LNA) is designed to achieve a flexible gain control of LNA. The proposed VG-LNA is implemented in TSMC 0.18 um CMOS process. This is composed of two stage amplifier, and its gain is controlled by the shunt feedback loop made up of a gain control transistor (GCT) and a coupling capacitor in second stage. The channel resistance of GCT in the shunt feedback loop influences the input and output stages of a second stage by the Miller effect. Total gain control of the proposed VG-LNA is implemented by two factors, the load impedance reduction and the interstage mismatch by controlling the channel resistance of the GCT. Consequently, by adding a shunt feedback with a gain control transistor, this proposed VG-LNA achieves both wide gain tuning range of 37 dB and a continuous gain control simultaneously. Secondly, 2.4 GHz low power folded RF front-end is designed for low power consumption. The proposed RF front-end is implemented in TSMC 0.25 um CMOS process for low power applications such as Bluetooth or ZigBee. The designed low power folded RF front-end applies for the folded and current reuse techniques. By using these techniques, the proposed RF front-end consumes 13.8 mW from 1.7 V supply voltage, while 5.2 dB NF and 27.5 dB conversion gain are achieved. In addition, by PMOS switch used in the switching stage of the folded mixer, a low flicker noise of 7 dB at 10 kHz is also achieved. Therefore, the proposed RF front-end can be used in DCR architecture for a narrow bandwidth system.