Front-end circuit design for wireless broadband communication system applications

This dissertation presents a broadband LNA with superb gain flatness demonstrated in 0.18mum CMOS for IEEE 802.11a or equivalent WLAN transceiver system applications. The key components of the proposed LNA are AMER inductors. Unlike passive inductors, AMER inductors can achieve a higher quality factor; linearity and power consumption are both superior to gyrator-based active inductors. When adjusting the gate voltage of the MOS device in the AMER inductor, the quality factor can be tuned. Using this adjustable Q characteristic of the AMER inductor to design an LNA, gain and bandwidth can be boosted simultaneously and gain fluctuation within 4.9∼5.9 GHz can be suppressed. The inherent noise problem of the AMER inductor doesn't deteriorate the noise figure of the overall LNA due to the three-stage architecture of the broadband AMER LNA. The first stage is designed for 50 O input matching, low noise figure and provides adequate gain to suppress noise coming from Stage 2 and Stage 3 which adopt AMER inductor loads to boost the overall gain and increase the bandwidth. Measurement results show that the broadband AMER LNA achieves a quasi-constant gain of 20.2 +/- 0.25dB or 18 +/- 0.15dB across the whole 1 GHz band. Each AMER inductor consumes only 0.1∼0.3mA in current. The noise figure of the LNA is measured as 2.6--2.7 dB within the intended frequency range. The measured IIP3 is about -0.5 dBm. The measured input and output return losses are both less than -10 dB. This broadband AMER LNA has been demonstrated to meet the requirements of IEEE 802.11a and equivalent WLAN transceiver systems.