A fully integrated 2×2 MIMO dual-band dual- mode direct-conversion CMOS transceiver for WiMAX/WLAN applications

Abstract

Growing demand in the broadband wireless communication market has resulted in emerging standards such as IEEE 802.16e (mobile WiMAX), which enable high data-rate communication over wide area coverage. Seamless switching between WiMAX and WLAN is envisioned as a means to enable users to stay connected anywhere and anytime. A low-cost low-power small-form-factor dual-mode (802.16e and 802.11b/g/n) dual-band (2.3G to 2.7G and 3.3G to 3.9G) 2x2 MIMO direct-conversion radio in 90 nm CMOS has been developed to address this rapidly growing market. The transceiver supports wide dual-frequency bands and multiple signal bandwidths of 3.5, 5, 7,10,14, 20, and 40 MHz for worldwide dual-mode operations. Many key challenges in WiMAX direct-conversion transceiver design stem from its small subcarrier spacing, which is necessary to combat multipath fading of OFDM signals in 125 km/h mobile vehicular environments. With the first subcarrier as close as 7.8125 kHz to DC, stringent requirements are imposed on RX and TX flicker noise, TX LO leakage, and LO settling time. Flicker noise in RX is greatly reduced with the adoption of a passive mixer. Several other circuit techniques, system optimizations, and build-in self-calibrations including DC offset with dynamic bandwidth control, IQ mismatch, TX LO leakage, filter bandwidth, LO frequency and amplitude calibrations are used to accomplish high transceiver performance. The chip also achieves excellent WiMAX/WiFi/BIuetooth/GPS/cellular co-existence performance owing to high RX linearity, robust high dynamic range RX AGC with smart blocker detection, and low TX noise. Ultra-wide RX input-signal dynamic range with EVM of better than -35dB to support MIMO 64-QAM OFDM application is achieved. A well-balanced TX gain control scheme is devised to obtain a very wide range of output power with EVM better than -35 dB.