Bermai to sample single-chip 802.11a radio

By
EE Times
(04/29/02, 01:54:36 PM EDT)

MANHASSET, N.Y. Fresh off an initial financing round that brought in $15 million, Bermai Inc. (Palo Alto, Calif.) is close to sampling an all-CMOS IEEE 802.11a-compliant 5-GHz radio transceiver that integrates the RF (with power amplifier), baseband and media-access control sections on one chip. The chip will come with hooks for an IEEE 802.11b-compliant RF front-end as well for upcoming 802.11g radios.

Other solutions to date, including those from Atheros Communications, have comprised at least two chips, namely the RF section and an integrated baseband/MAC.

President and CEO Bruce Sanguinetti said Bermai overcame the limitations of CMOS at 5 GHz by tapping the RF expertise of co-founders Ramesh Harjani and Jaek Yun Moon. The founders pulled together a team from varied sources to tackle the single-chip design from four perspectives: integration, range and coverage, data rates and power efficiency.

"Having discrete parts matched to 50-ohm impedances and operating at [5-GHz] frequencies is a great drain on power," Harjani said. To get everything on one chip, the company practiced the usual black arts of partitioning, isolation, ground and power lines, filtering, channel selection and power-amp temperature monitoring. It also built a proprietary RF architecture that is neither direct conversion nor low-IF but a "a combination that overcomes the drawbacks of both," he said.

Market limiters

The drawbacks of direct conversion dc offset, local-oscillator pulling and CMOS flicker noise have prevented its use at 2.4 GHz, "except for relatively undemanding radios, such as Bluetooth," said Moon. And image rejection plagues low-IF radios.

The Bermai architecture's adjacent-channel rejection varies from 16 dB at 6 Mbits/second to 0 dB at 48 Mbits/s. "We meet or exceed adjacent-channel requirements for all data rates," said Harjani. The design also provides immunity from even-order nonlinearity artifacts, with a 9- or 10-dB compression point.

An advanced phase-tracking algorithm and precise sync detection allow the use of 256-QAM modulation of the OFDM carrier. "This allows 72-Mbit/s data rates in a single channel," said Harjani. Rates beyond the 54 Mbits/s outlined in 802.11a have been achieved by Atheros and others, but such implementations have used two channels.

The 72-Mbit rate is achievable over a 38-foot range, said Moon.

Power consumption for the BER7211a radio is 900 mW for full steady-state transmit and 500 to 600 mW for receive mode. Implemented in 0.18-micron CMOS, the radio caters to the lower two 802.11a bands and is priced at under $35 per 10,000.

Bermai expects to sample after midyear. Target markets are enterprise, fixed wireless access and home entertainment.