industry femtocells
The femtocell market is expected to expand to approximately 49 million access points by 2014, according to the industry organization Femto Forum. By then 114 million users across the globe will be accessing mobile networks via femtocells. Considering that these small cells contain all the functional elements of a traditional base station, the importance of the RF power amplifier (PA) module becomes apparent.
To enjoy significant commercial success in this growing market, the femtocell design must balance features, functionality and pricing. For the PA, these requirements translate to characteristics that include exceptional RF and DC performance, multi-mode support, multi-standard support and reliability. The biggest factor that influences all of these characteristics is the semiconductor process used to manufacture the PA itself.
Figure 1. Anadigics has recently developed the AWB7227 power amplifier module with a rated power of 27dBm. This balanced design that is slated for release later this year can be used to amplify the waveforms of the most demanding air interfaces such as CDMA, WCDMA, and LTE. When driven with a WCDMA waveform – test mode 1, 64 channel waveform, and a 10.5 dB peak-to-average ratio – this high-performance amplifier has margin to the ACOP requirement
Going with GaAs GaAs-based chips are employed in the vast majority of mobile handsets, as well as many components for low- to mid-power infrastructure. By building devices around this material it is possible to create amplifiers delivering great performance at competitive prices, and there is every reason to believe that this material will be widely used to build the amplifiers deployed during the build-out of 3G and 4G networks.
For the last ten years or so most PAs have been built from GaAs-based HBTs. Initially these transistors combined GaAs with AlGaAs, but more recently alternatives employing the pairing of GaAs and InGaP have been introduced that offer superior performance.
At Anadigics, which is based in Warren, NJ, we have built upon the huge success of the InGaP/GaAs HBT. Our InGaP-Plus process combines bipolar and FET devices on the same GaAs die, a move that allows features usually residing off of the chip to be integrated into conveniently sized, surface mount parts. The upshot is that switches, step attenuators, power detectors, and voltage regulators are commonly found in our PAs.
Figure 2. The AWB7227 amplifier is capable of supporting multiple carriers, a feature that can be useful in certain deployment scenarios. Each carrier represents a group of users operating at a particular frequency. Here, the device has been subjected to 2 WCDMA Test Mode 1, 64 DPCH carriers at maximum separation
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www.compoundsemiconductor.net October 2010
Pioneering RF Performance We are currently designing a family of balanced and single-ended power amplifier modules for use in femtocells, picocells and in-home customer premises equipment. Each of our modules is specifically designed to deliver optimal performance in one or more of the several popular frequency bands used by wireless carriers. While specific features vary from module to module and are based on the target application, the design approach for each is similar.
The availability of a family of devices offers significant advantages to design teams, which may be tasked with
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