Anyone following the device market for cellular handsets knows that key areas of focus include size, power consumption, and overall cost. Things get especially challenging for the North American cellular market, where many handsets require dual-band power amplifier (PA) functionality to support both cellular and PCS frequencies. Alternatives include using two single-band PA modules, which could measure as large as 4 x 4 mm each, or a dual-band module, such as the new AWT6310 PA from Anadigics.
The AWT6310 product family was a natural evolution for the design team at Anadigics, and was based on technologies developed for their single-band 3x3 mm PA modules that were already in production. The driver behind the development of this product is that RF design teams are struggling as their available board real estate shrinks to make way for adding multimedia functionality to wireless phones.
"Our new dual-band PA module is approximately 7% smaller than competing dual-band modules, and it offers at least a 25% reduction in PCB area as compared with two single-band PA modules," explains Jerry Miller, Product Line Director CDMA/WCDMA for Anadigics.
Key concerns for handsets include long battery life and long talk time, and, for the PA, this is influenced primarily by power added efficiency. The new PA typically features impressive efficiency of 39 to 41%. Another key concern is adjacent channel and alternate channel power, which, with insufficient rejection, could cause dropped calls. The AWT6310 demonstrates typical adjacent channel power ratio of -50 dBc and -62 dBc for alternate channel power.
In addition to hitting the key specs and shrinking the package size, this new design simplifies the PA control by combining the Vcc high bias and low bias modes into a single mode pin.
The design team did something else interesting: they produced two versions of the product where the Vcc, Vmode, and RF pins are mirror footprints of each other. Specifically, in the AWT6310, the Vmode pin out is PIN3, in the AWT6314, Vmode goes to PIN4. The team did this to accommodate current transceiver pin outs, as well as to work with new transceivers on the horizon that have the pin outs flipped or reversed.
What were the major design challenges? "To achieve a small size form factor, and to maintain the performance expected of us," says Miller. "We devised the regional definition, then the engineers worked the layout, and we settled on the 3x5mm rectangular package, which lends itself to a natural flow across the phone board." The final transmit chain features RF filters between the transceiver chips and the PA, and duplexers between the PA and antenna.
In terms of processing, the team used the company's InGaP HBT process that has been in production for approximately four years. "We've been shipping CDMA PA modules using this process since 2001," notes Miller, "so we have confidence in this proven process to produce high-performance, linear power amplifiers."
So, what's next? The Anadigics design team sees multiband PAs as a step towards being able to support higher levels of integration. While the company is eyeing other multiband markets, it is also keen on supporting single-band markets, such as China and India with its 3x3 single-band PA modules. "There is also the possibility of combining cellular CDMA and WCDMA in this type of module as well," suggests Miller.
