Electronic Design

Monolithic CMOS Power Amplifier A First For GSM Cell Phones

Power amplifiers (PAs) for GSM cell phones tend to be separate chips made from expensive gallium-arsenide heterojunction bipolar transistors or silicon-germanium bipolars. In fact, many cell-phone PAs are actually complete modules made up of multiple chips plus a handful of discrete components that don't integrate well. Yet Silicon Laboratories does away with all of that old technology, space, and cost with its Si4300 breakthrough PA for GSM cell phones.

Using standard 0.35-µm digital CMOS, this single-chip PA offers the benefits of low cost because it can use standard, widely available CMOS process technology. On top of that, it integrates the PA as well as all of the related complex functions on a single die. It reduces board space by 70% and the component count by 90% in a typical cell phone.

Since GSM phones employ Gaussian minimum shift keying (GMSK), a type of frequency shift keying with a constant envelope (amplitude), nonlinear power amplification techniques that are more efficient may be used. The Si4300 PA uses class E switching amplification. With its patented circuit techniques, the amplifier overcomes gate-voltage-breakdown problems to achieve the high power at the high battery voltage a GSM PA needs.

The Si4300 is a dual PA: one for GSM low bands (800 to 900 MHz) and the other for DSC high bands (1800 to 1900 MHz). Typical power output is 33 dBm ±2 dB for GSM phones and 30 dBm ±2 dB for DSC phones. Its efficiency is comparable to competitive solutions at all power levels. The Si4300 also is compatible with General Packet Radio Services (GPRS) Class 12, and it will find homes in GPRS multislot applications.

In addition to the PA, the Si4300 integrates all of the circuitry between the antenna switch and the transceiver (see the figure). This includes the automatic power control circuitry, thermal and load mismatch protection, harmonic filtering, and 50-Ω input and output matching networks. An included digital serial interface ties to the the company's Aero GSM cell-phone transceivers.

The Si4300 is packaged in a 3.9- by 6.4- by 1.3-mm land-grid-array (LGA) package with 18 pins. In 10,000-unit quantities, pricing starts at $2.82. Samples are available now, with full production in the third quarter.

Silicon Laboratories Inc.
www.silabs.com
(512) 416-8500

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