A 2.5 GHz BiCMOS transceiver for wireless LAN

Abstract

A low-cost Si IC contains most of the elements required to realize the RF transmit and receive paths of a 2.5 GHz WLAN transceiver meeting 802.11 requirements. External filters and a power amplifier complete the RF front-end. The 2.73 mm/sup 2/ die is mounted in a 24-pin plastic package (TSSOP24). A low-noise amplifier (LNA) is switchable between high (14 dB) and low-gain (-13 dB) modes. High-gain mode with 2.2 dB NF, P-1dB=-15dBm input and IP3=-3dBm input is utilized in weak signal conditions. Low-gain mode with P-1dB=+5dBm input and IP3=+17dBm input can be selected in moderate-to-strong signal conditions. The signal goes off-chip from the LNA to an external image-rejection filter and is then input to the receive mixer via pin 19, that is also shared by the upconversion mixer output. This allows use of the same external filter in both transmit and receive modes. Both mixers are driven by an on-chip local oscillator (LO) buffer that has full-frequency and half-frequency input options, selectable via the LO switch at pin 11. An on-chip frequency doubler in the LO buffer with on-chip LC filters deliver a full-frequency LO signal to the selected mixer with half-frequency LO inputs.