802.11a/b Card: Downconversion delivers

As with most WLAN cards, a chipset and reference design from the IC supplier drives much of the design. The WAB501 system architecture is based on the Atheros Communication AR5001X Combo WLAN chipset which consists of the AR5211 Multiprotocol MAC/baseband processor, the AR2111 2.4-GHz "Radio-on-a-chip," and the AR5111 5-GHz "Radio-on-a- Chip." Testimony to the advancing state of RF-capable IC processes, both radio chips use pure CMOS, despite the 2.4 and 5GHz carrier frequencies. In addition to the Atheros chipset, there is a M/A-Com DP2T transmit/ receive diversity antenna switch, a Volterra VT102 power management chip and two GaAs power amplifiers.

Worth noting is the use of 5GHz as the primary transceiver band; operation in the 2.4 GHz AR2111 entails downconversion or upconversion of the signals leaving or entering the AR5111 chip (for transmit and receive respectively). Because the more complex transmit and receive circuitry is implemented only once in the AR5111 chip, cost and power benefits are likely to be achieved in the companion AR2111 which primarily implements the simpler and lower-consumption up/down conversion circuits.

With components on only one side of the CardBus format PCB, the WAB501 dedicates about two-thirds of the assembly space to the largely analog radio, including diversity antennas and their associated ground plane. A 10:1 ratio of discretes to semiconductor devices further speaks to the still-rich analog content needed for WLAN card implementation. In fact, well over half of the roughly $35 bill-ofmaterials cost for the WAB501 comes from these analog components, a nice opportunity indeed.

David Carey is President of Portelligent (www.teardown. com). The Austin, Texas company produces teardown reports and related industry research on Wireless, Mobile, and Personal Electronics.