Silicond-Germanium Amplifiers Boost 3G WCDMA And 802.11a Radios

May 10, 2004
Making an integrated power amplifier for microwave radio has never been easy. In the past, most manufacturers settled on gallium-arsenide (GaAs) amplifiers to wring out the most performance. But their high cost keeps the bill of materials (BOM) of...

Making an integrated power amplifier for microwave radio has never been easy. In the past, most manufacturers settled on gallium-arsenide (GaAs) amplifiers to wring out the most performance. But their high cost keeps the bill of materials (BOM) of cell phones, wireless local-area networks (WLANs), and other wireless products high. A proven solution is the use of silicon-germanium (SiGe) semiconductor materials that offer GaAs performance but can be made in silicon fabs, thereby greatly reducing costs.

Recently, SiGe Semiconductor expanded its power-amplifier (PA) product line to include wideband code-divsion multiple access (WCDMA) 3G cell phones and the higher-speed 802.11a WLAN products. One new entry, the RangeCharger SE5120, targets the growing WCDMA 3G cell-phone market. This three-stage linear amplifier operates in the 1920- to 1980-MHz range. It features a peak output power of +28 dBm with a linearity of −38 dBc, and power-added efficiency runs above 40%.

Integrated in the device are the amplifier, regulator, matching circuitry, and optional power detector. Also included are bias and gain control circuitry as well as on-chip electrostatic discharge and load mismatch protection. It can sustain a voltage standing-wave ratio mismatch up to 10:1. Separate power pins to the control and amplifier cells help designers regulate the amp's VCC and improve efficiency at lower power levels. Its sleep mode uses a standby current of 2 µA.

The SE5120 comes in an eight-pin QFN package that measures 3 by 3 by 0.9 mm. Pricing in 100,000-unit lots is $1.50. The company claims that due to all of the integrated circuitry, a system BOM reduction of up to $2.80 is possible.

Another new SiGe PA is the SE2535 (see photo). Designed for the 802.11a 5-GHz Wi-Fi band, it solves the wide bandwidth problems associated with orthogonal frequency-division multiplexing (OFDM), the modulation method used in 802.11a. An error vector magnitude (EVM) of less than 2.5% at 18 dBm can be achieved.

This chip houses a linear, three-stage, 27-dBm power maplifier that incorporates a power detector and all of the analog biasing and matching circuitry into a standard QFN package measuring just 4 x 4 x 0.9 mm. The power detector adjusts the operating point to accommodate the peak-to-average power ratio, saving power while maintaining performance. The current drain is 160 mA for +18 dBm output.

The SE2535 meets the 802.11a harmonic requirements of worldwide standards bodies and eliminates the need for external bandpass filtering. A power detector is fully integrated. All of these features translate into a smaller form factor and a lower BOM cost. Available now, the SE2535 costs $1.75 in 100,000-unit quantities.

SiGe Semiconductorwww.sige.com

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