Design method for a reconfigurable CMOS LNA with input tuning and active balun

Abstract A method to design a tunable low noise amplifier (LNA) for multiband receivers is proposed. This paper also presents a single-ended to differential conversion (S2DC) topology which improves the LNA linearity without degrading its noise performance. Combining input tuning with S2DC in a single stage reduces power consumption of the LNA and decreases effects of supply noise. An LNA has been designed based on the proposed method for 2.3–4.8 GHz in a 0.18 μm CMOS technology. Simulations show an IIP3 of −3.2 dBm, a less than 3.7 dB noise figure (NF), a voltage gain of 24 dB in the whole frequency range. The LNA draws 13.1 mW from a 1.8 V supply. The results indicate that the proposed tuning method satisfies the input matching requirement and attenuates out of band interferers at the input, before they get amplified through the first transistor. Thus, it provides a superior out of band IIP3 compared to the LNAs with output tuning. Linearity simulation with in-band interferers shows that the proposed negative feedback technique in the S2DC topology enhances in-band IIP3 by about 5 dB compared to the topology without the negative feedback. Therefore, the proposed method relaxes the trade-off between linearity and noise performance in LNAs with active-balun.