Design and analysis of an LNA for WLAN direct-conversion receiver

Abstract

IEEE 802.11a standard is established by the need of high data rate, which provides 54 Mbps or more. IEEE 802.11a are based on orthogonal frequency division multiplexing (OFDM) for robustness against intersymbol interference originated from multi-path effect. In this paper, two stages differential LNA of direct-conversion receiver for IEEE 802.11a is designed, implemented, measured, and analyzed. To design an LNA, 802.11a standard is analyzed, and system level specifications such as noise figure (NF), and $3^{rd}$ order intercept point (IIP3) are discussed. System level specifications are distributed to block level like band pass filter, LNA, mixer, and analog block. The results of block level design are used in circuit level design. Schematic simulation results of a differential LNA have 17.8dB of gain, -16dB of S11, -16dB of S22, -5dBm of IIP3, and 24mA of current with 2V of supply voltage. After implementation, the performances of chip are measured. Because the results are degraded, the causes of the degradation are analyzed and found in this paper. Then, the LNA is redesigned. The post-layout simulation results of the redesigned LNA have 2.9dB of noise figure, 15.35dB of gain, -16dB of S11, -23dB of S22, -9.5dBm of IIP3, and 24mA of current consumption with 2V of supply voltage.