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Prompted by growth in the wireless marketplace, Analog Devices has unveiled a transceiver chip that shrinks the radio size in cellular telephones to as little as 1.5 square centimeters. The AD6548, the latest addition to its Othello family of direct-conversion transceivers for GSM/GPRS handsets, enables a complete quad-band radio that is 30% smaller than anything available on the market, according to ADI. Also called Othello-G radio, it supports full quad-band operation and integrates virtually all the necessary components, such as voltage-controlled oscillators (VCOs) and the associated tank circuits, phase-locked loop (PLL) filters, and power management circuits, for a complete cost-effective, ultracompact cellular handset radio design. The only external components required for a complete radio design are the receive surface acoustic wave (SAW) filters, power amplifier, transmit/receive switch, and a few passives. Othello-G features four fully integrated programmable gain differential low-noise amplifiers (LNAs) for full quad-band (GSM850/900/1800/1900) support. The AD6548 uses a single integrated local oscillator (LO) VCO for receive and transmit circuits. The LO is generated with a fast-locking fractional-N PLL synthesizer with integrated loop filters, Tx and Rx VCOs and tank circuits (see the figure). The synthesizer lock times are optimized for GPRS applications up to and including class 12.

To dramatically reduce the radio bill of material (BOM) cost, the synthesizer integrates a loop filter and incorporates a complete reference crystal calibration system. The translation-loop transmitter architecture eliminates the need for external filtering between the transceiver and power amplifier. In addition, the AD6548 includes on-chip voltage regulators with independent power-down controls, enabling direct-to-battery connection, minimizing power consumption, and eliminating the need for external regulator components. In fact, according to the maker, the Othello-G radio chip enables a fully functional reference design with approximately 75% fewer components than its previous version.

Implemented in 0.35 micron BiCMOS process, the AD6548 offers sensitivity in the -109 dBm to -110 dBm range for 2.4% bit error rate. Other key specs include 77 dB of gain control range, 26 MHz crystal frequency and 10 microamperes maximum power-down current (battery voltage present, regulators in shutdown mode, registers kept alive). Operating voltage range for the radio chip is 2.9 V to 5.5 V. The specified temperature range for the device is -20° C to +85° C. Sampling now, the AD6548 comes in a 32-lead LFCSP package and is priced at $3, in 10k units.
Analog Devices Inc.
(781) 937-1428
www.analog.com

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