A Robust CMOS Bluetooth Radio/Modem System-on-C B luetooth is designed to be a global, low-cost,low-power,and short- range radio technology. To achieve the low-cost requirement, a simple modu - lation scheme and relaxed RF constraints are defined. This allows a reduced com - plexity RF/analog implementation archi - t e c t u r e , w h i c h t o g e t h e r w i t h t h e short-range requirement helps to achieve the low-power requirement. The globally available requirement is reached by using the worldwide, unli- censed industrial, scientific,and medi - cal (ISM) band. The drawback is that the ISM band is used by many RF devices for different applications and standards that “pollute” the frequency band with noise and interferers. One of the meansto make the communication more robust and tolerant to this “pollution” is to di - vide the band into channels, split the transmitdata into smallpackets,and send the packets on different channels using a pseudorandom frequency-hoping scheme. This means that, if a packet is lost because of an interferer on a certain channel, it will be retransmitted on a dif- ferent channel. The need of recurring frequency hops infer a radio solution with a tunable fre - quency synthesizer to be able to trans - mit/receive on different channels. With the relaxed constraints on the RF/analog implementation in the Bluetooth specifi - cation,following the requirements for low cost/low power, the solution is likely—and permitted—to have a certain frequency offset and drift, related to the ideal channel center frequency. This im - perfection has to be accounted and ad - justed for, to be able to meet the bit-error-rate (BER) requirement. In this article we will discuss a DSP mechanism for adjusting frequency offset and drift to achieve a robust Bluetooth performance in the Spirea Bluetooth 0.18 CMOS ra - dio/modem system-on chip (SoC) solu- tion, BlueTraC. BLUETOOTH STANDARD The Bluetooth standard includes a few fre - quency-correction-related requirements: ✦ Packets: Three different packets are defined based on a slot concept. A slot is a numbered 625-ms-long time period during a connection between two (or more)Bluetooth units. A transmit or a receive hasto be aligned to a slot. The master (the main unit in the connection) is al- waystransmitting on even-num- bered slots, and the slave (the secondary unit in the connection) is always transmitting on odd-num- bered slots. A DH1 packet occupies one slot,a DH3 packetoccupies three slots, and a DH5 packet occu- pies five slots. ✦ Offset: A transmitted initial channel frequency must be within ± 75 kHz from the ideal center frequency. ✦ Drift:During transmit the synthe - sizer is allowed to drift ± 25 kHz for DH1 packet and ± 40 kHz for DH3 and DH5 packets. ✦ Modulation: Since binary data can - not directly be transmitted over an air interface, the signalhas to be modulated in some way.When choosing a modulating scheme there is a tradeoff between: spectral efficiency, simplicity and power con - sumption ofmodulator/demodu - lator,and power efficiency in the poweramplifier.The goalof the Bluetooth specifications is to make the hardware implementation inex - IEEE CIRCUITS & DEVICES MAGAZINE ■ NOVEMBER 2002 8755-3996/02/$17.00 ©2002 IEEE 7■ The CHIP M. Ismail and N. Tan, Editors By Fredrik Westman, Fredrik Jonsson, Tommy Öberg, Christer Hedqvist, and Ahmed Hemani Editors’ Note: Welcome to the Chip! The article in this column discusses a design technique exploiting digital technology to provide robustness to the analog and RF parts of a wireless system-on-chip (SOC), a Bluetooth radio/modem. Using digital to provide robust analog will become more trendy particularly when migrating to smaller feature size processes where random process varia - tions could cause severe degradation in analog and RF performance and where digital still follows Moore’s law and hence would be a cost-effective solution to re- store analog performance. We hope you find the article enjoyable. We also encourage you to continue to e-mail us with your comments and contributions (Ismail@ee.eng.ohio-state.edu or ntan@globespan.net). We wish you all a very happy holiday season and a wonderful new year for 2003! —Mohammed Ismail and Nick Tan