Compact small signal modeling and PSO-based input matching of a packaged CMOS LNA in subthreshold region

Abstract

The paper reports a small-signal model of a cascaded, packaged, CMOS low noise amplifier (LNA) operating in subthreshold region. The proposed compact model has been verified through CADENCE simulations in standard 0.18 μm process. This model also accounts for the dominating role of some of the device parasitic capacitances in determining the input impedance of the amplifier. The closed form expression of the input impedance obtained-from this model is then used for synthesizing the input matching network of the common-source LNA using standard Q-based technique. It has been noted that the conventional Q-based matching approach does not provide symmetric matching characteristics ( S 11) about the center frequency (900 MHz). To overcome this problem, a swarm intelligence-based evolutionary technique has been adopted for synthesis of the matching network. Symmetric nature is obtained both in terms of S 11 as well as the real/imaginary parts of the input impedance.