Electronic Design

Chirp Modulation Propels Micropower 2.4-GHz ISM Wireless Transceiver

By applying a chirp spread-spectrum technique to multidimensional-multiple-access (MDMA) modulation, scientists at Nanotron Technologies of Berlin, Germany, produced an optimized single-chip transceiver for wireless communications in the 2.45-GHz ISM (Industrial, Scientific and Medical) band.

The silicon-germanium (SiGe) implementation yields a highly sensitive IC, with less than -92 dBm at a bit-error rate of 10-3. This short-distance IC also operates up to 600 m indoors and 700 m outdoors. It requires very low power, typically 1 µA and a maximum of 4 µA in standby, so battery operation can last for several years from a small cell. The 0.35-µm SiGe biCMOS chip takes up just 10 mm2 of die area as well.

Chirp impulses are linear FM signals with constant amplitude that resist transmission disturbances. MDMA modulation combines amplitude, frequency, and phase to exploit the best performances of all three for applications with medium data rates and extremely low power.

Sync impulses that provide a small bandwidth-time (BT) product deal with signals at the transmitter and receiver. Once out of the transmitter, signals are "chirped" to obtain a large BT product. Two dispersive delay lines are located at the transmission and reception end points (Fig. 1).

The mixed-signal nanoNET TRX transceiver's baseband media-access controller (MAC) provides a minimum data rate of 2 Mbits/s. It supports four modulation modes (up-chirp/null, down-chirp/null, folded chirp, and quaternary chirp) and includes a 4-bit programmable port and a four-channel analog-to-digital converter (ADC) (Fig. 2). Also, it runs from an unregulated 2.38 to 3.6 V.

The chip will be housed in a 7- by 7-mm 48-pin MLF package. A demonstration board is available now, with samples arriving in February 2003. Evaluation boards will be available in April 2003. In 100,000-unit lots, the chip will cost 7.5 Euros ($7.33 U.S.), going down to 5 Euros ($4.88 U.S.) for a CMOS version in 2005.

For details, call +49 30 399 954-137 or go to www.nanotron.com.

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