Electronic Design

Single-Chip Transceiver Brings 3G Handsets Up To Speed

The SW3200 integrates CMOS and WEDGE/HSDPA RF functionality for next-generation performance.

The wait for 3G was like being stuck on hold, listening to an unending loop of the Muzak take on "The Wayward Wind." Fortunately, the wayward winds of 3G have stopped blowing, because its cell phones have finally arrived. And with 3G networks up and running in most major cities, service is finally available, too.

Unfortunately, to this point, handset-manufacturer response has lagged. But the pace should pick up now, thanks to a faster, better way to implement a lower-cost 3G handset that consumes less power.

Sirific Wireless Limited's SW3200 single-chip 3G transceiver is the first product in the company's Nexus III family of CMOS 3.5G RF transceivers. Its high-speed downlink-packet-access (HSDPA) feature brings much faster data performance than the UMTS WCDMA standard's 2-Mbit/s maximum.

Wideband CDMA 3G transceivers must be backward-compatible with previous generations of cell-phone systems, namely GSM, GPRS, and EDGE—thus the name WEDGE. The SW3200 handles GSM and its GPRS and EDGE (Class 12) data formats. It covers all four standard GSM bands, including 850, 900, 1800, and 1900 MHz. Furthermore, it supports the worldwide WCDMA bands I, II, III, IV, V, and VI.

Band I is 2.1-GHz RX and 1.9-GHz TX in Europe and Asia. Band II is the North American 1.9-GHz PCS band. Band III is Japan's 1.7-GHz band. Band IV is the North American 2.1-GHz RX and 1.7-GHz TX. Band V is another North American band at 850 MHz. Band VI is a Japanese allocation. Recall that WCDMA of the UMTS standard specifies frequency-division duplexing (FDD) in 5-MHz wide channels.

LOOKING INSIDE
The SW3200's front end consists of an antenna switch, surface-acoustic-wave (SAW) filters for the four GSM bands, and additional SAW filters for the WCDMA bands. WCDMA also requires duplexers. The external power amplifiers are linears. The transceiver is direct conversion. In the GSM RX section, the incoming signals are down-converted to baseband and then digitized by the internal analog-to-digital converters (ADCs). The ADC outputs go to the DigRF baseband interface.

A group of GSM chip manufacturers devised the DigRF interface standard, which eliminates the previous analog interface between the receive I and Q signals and the baseband. In older designs, the I and Q analog signals were sent to the baseband chip for analog-to-digital conversion. Now the ADC is on-chip, and the interface between the transceiver and the baseband is digital.

The transmit (TX) interface is also digital. Signals from the baseband are first digitized and sent to the transceiver via the DigRF interface. The conversion back to analog occurs in the transceiver. The I and Q mixers then upconvert the signal to the final frequency. (AΣ-Δ fractional-N synthesizer with patented phase-locked loops is on-chip, too.)

The digitally compensated crystal oscillator-(DCXO) requires an external 26-MHz crystal. Support is provided for an external temperature-compensated crystal oscillator (TCXO) if desired. The processes in the WCDMA section are similar, but without the DigRF interface.

The SW3200 works with a variety of existing baseband chips. The WCDMA section also features the HSDPA data capability. With Category 9 capability using 16-QAM (quadrature amplitude modulation), a data rate of up to 10.2 Mbits/s is possible.

The receiver (RX) for the SW3200 features concurrent WCDMA and GSM/EDGE RX operation, as well as a smooth handoff between WCDMA and GSM/EDGE. According to Sirific, the SW3200's estimated RX sensitivity is 2 dB lower than the competition.

As for the TX, it doesn't need an external GSM/EDGE filter. Its on-chip power control offers 40-dB dynamic range for EDGE and a 90-dB range for WCDMA. A three-wire serial peripheral interface is provided for WCDMA control.

The SW3200, housed in a 7- by 7- by 1-mm LGA package, also allows for a high level of integration. Compared to competitive designs that use two to four chips, the transceiver can save over 150% of board space, according to the company. The technology is 130-nm CMOS. Overall 3G power consumption is estimated to be 15% lower than the competition.

An EM3200 evaluation module for handset designers costs $950 (see the figure). The SW3200 is sampling now, with full production expected later in the year. Prices start at $7.95 for 10,000-unit quantities.

Sirific Wireless Limited
www.sirific.com/nexus3.htm

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