AN3179| Application Note
Maxim > App Notes > WIRELESS, RF, AND CABLE Keywords: MAX2820, MAX2821, MAX2822, MAX2242, 802.11, wlan, board of bill, transceiver
Apr 08, 2004
APPLICATION NOTE 3179
802.11b WLAN Transceiver Shrinks Circuit Board and Bill of Materials
Abstract: IEEE 802.11b wireless networks have become a key element of enterprise networks. They provide convenient access to network resources for workers carrying portable computers and handheld devices and for guests or temporary workers. They are finding wide application in public environments such as hotels, airports, and coffee shops. They also provide a cost-effective alternative to relocating physical Ethernet jacks in environments where facilities are moved or changed frequently. To serve this fast-growing, emerging market, Maxim has developed a complete RF solution (RF transceiver and power amplifier) that meets the requirements of the IEEE 802.11b WLAN (wireless local area network) standard. Wireless networks provide convenient access to network resources for workers carrying portable computers and handheld devices, and for guests or temporary workers. Those networks are finding wide application in public environments such as hotels, airports, and coffee shops. They also provide a cost-effective al
ternative to relocating physical Ethernet jacks in environments where facilities are moved or changed frequently. The MAX2820 and MAX2821 are single-chip zero-IF (intermediate-frequency) transceivers designed for 802.11b (11Mbps) applications operating in the 2.4GHz to 2.5GHz ISM (industrial-scientific-medical) band. The transceivers are nearly identical, except that the MAX2821 provides low-power shutdown and analog-voltage reference-output, while the MAX2820 does not. The transceivers include all circuitry required to implement an 802.11b RF-to-baseband transceiver solution, providing a fully integrated receive path, transmit path, VCO, frequency synthesis, and baseband/control interface. To complete the radio front-end solution, only an 802.11b dedicated PA like the MAX2242, an RF switch, an RF BPF (bandpass filter), and a small number of passive components are needed. The devices are suitable for the full range of 802.11b data rates (1Mbps, 2Mbps, 5.5Mbps, and 11Mbps), and also the higher rate 22Mbps PBC
CTM (Packet Binary Convolutional Code) standard from Texas Instruments. The MAX2820 and MAX2821 are available in the very small, 7mm x 7mm, 48-pin QFN/ thin QFN packages. The MAX2820-MAX2242 chipset complements Maxim's capabilities in other wireless areas, including cdma2000/ W-CDMA chipsets, multimode transmitter ICs for GSM/GPRS, and enhanced data rates for global evolution (EDGE), zero-IF (ZIF) direct satellite receivers and transmitters.
The ZIF Transceiver
The homodyne (ZIF) approach used in today's highest performing solutions results in a typical receive sensitivity of -87dBm at 11Mbps (-97dBm Rx sensitivity at 1Mbps) with Maxim's reference designs. This sensitivity is 2dB to 3dB better than other homodyne solutions and 1dB to 2dB better than other heterodyne solutions. The surface acoustic wave (SAW) filter from a heterodyne transceiver might appear to provide an advantage in power consumption, because passive filters seem to allow lower supply currents. One must not forget, however, that heterodyne architectures need an RF mixer with additional power gain to compensate for the SAW filter's insertion loss. Active filters integrated within the transceiver are attractive as they allow a very low, 4.5dB worstcase noise figure for the whole receiver chain at a maximum gain condition (34dB at minimum gain condition). The on-chip-receive low-pass filters provide the necessary steep filtering that attenuates the out-of-band (>11MHz) interfering signals to sufficie
ntly low levels, thus preserving receiver sensitivity.
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