A compact dual-band direct-conversion CMOS transceiver for 802.11a/b/g WLAN

Abstract

Over the past several years, the WLAN market has shown more than double digit growth, dominated mostly by network interface cards and mini-PCI solutions. More recently, WLAN is beginning to penetrate into the embedded market, including applications in home entertainment, cellular phones, PDAs, and gaming. These embedded applications place stringent constraints on cost and power consumption. In this paper, a compact fully integrated 0.18µm RF CMOS transceiver is presented that meets the IEEE 802.11a/b/g WLAN requirements and covers both the 2.4-2.4835GHz and the 4.9-5.875GHz bands. The transceiver occupies 6mm 2 die area while consuming at most 182mW. Compared to previously published dual-band RF transceivers [1][2][3], this transceiver covers all bands specified for WLAN while achieving 50-70% smaller die area with 24-60% less power consumption.In the past, several radio architectures have been used to realize the RF transceiver [1][2][3][4]. Although two-step zero-IF architecture [1,2] decreases the LO frequency by separating the up/down conversions into two successive steps, this scheme doubles the number of mixers, LO drivers, and frequency synthesizers. Therefore, it is difficult to use this architecture for low-power, small-die-area implementations. In contrast, direct-conversion radio architecture requires only one LO to achieve up/down conversion in one step and therefore, leads to a more compact and low-power design. Thus, the dual-band transceiver is implemented based on the direct-conversion architecture as shown in Fig. 5.4.1. To overcome the well-known impairments due to LO leakage and DC offset, an LO calibration loop and a successively switched DC offset cancellation loop have been implemented in the transceiver. The LO calibration loop reduces the amount of LO leakage to less than -29dBc while the successively switched DC offset cancellation loop improves the cancellation and has a shorter convergence time, which is critical for the 802.11a/g modes.The transmitter shown in Fig. 5.4.1 includes separate up-conversion mixers and class AB pre-amplifiers for the 5GHz and the 2.4GHz bands, but shares a 5 th -order LPF that has a variable gain with 14dB tuning range. Because of device mismatches, LO leakage exists in the transmitter output, which in the worst case could be only 15dB lower than the desired signal. To reduce the LO leakage, an on-chip LO leakage calibration circuit as shown in Fig. 5.4.2 is implemented in the transmitter to guarantee at least -29dBc LO leakage with at most ±3dBc change on the image tone.The transmitter delivers 2.5dBm/1dBm output power with 20dBm/23dBm OIP3 for 2.4GHz/5GHz band while meeting the ACPR requirements for 802.11a/g with EVM of -31dB/-32dB. The output power flatness across 4.9GHz~5.8GHz is 4.5dB and with a variation of 3.5dB when temperature changes from 0 to 85 0 C. The TX output power can be further increased to 8.5dBm/6dBm for the 2.4GHz/5GHz band with the same power consumption but with a higher EVM of -28dB/-29dB.The receiver shown in Fig. 5.4.1 consists of ...