Teardown: LG's VX8300 Flip-Phone

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Some "Under the Hood" reports are harder to do than others, and not because the design has more screws or uses more glue than the norm. Sometimes it's hard to take apart a product simply because the product works so well, you don't want to destroy it (and I do destroy every product I dismantle).

LG Electronics' VX8300 flip-phone handset is one such product. I was loath to deconstruct this handset, because it does just about everything right. In fact, I liked it so much I got one for my personal use.

Weighing in at 3.88 ounces, the VX8300 has two bright displays, including a 65,000-color organic LED for the external display, and the keys are spaced comfortably. It offers Bluetooth 1.1 functionality and has a slot for a microSD memory card. Its user interface is highly intuitive. The phone is slightly larger than I would like (3.58 x 1.93 x 0.92 inches) and is designed with the dreaded external antenna stub. But I was willing to make those trade-offs for the quality this handset offers.

The phone's multimedia capabilities include Verizon Wireless' VCast music (using a pair of external speakers), video, polyphonic ring tone support and gaming. The GPS-enabled handset can access the Internet and contains a 1.3-Mpixel camcorder/camera with flash. The standard 1,100-milliamp-hour lithium-ion battery provides up to 230 minutes of use time or 380 hours of standby time.

LG designed the VX8300 internally. The company prides itself on having a fast time-to-market, so its IC suppliers must be ready to go to full production in just a few months if need be.

The unit's baseband functionality comes from Qualcomm's MSM6500 chip set. Power management, including voltage regulation, is handled by a Maxim device.

The RF quality is attributable to Anadigics' AWT6314R power amplifier (the "R" signifies RoHS compliance). The 3 x 5-mm device integrates two PAs into one package to enable operation over the 1.9-GHz CDMA PCS and 800-MHz CDMA (digital dual-band) frequencies. The result for LG is a reduced external-component count and an attendant savings in board space. Anadigics claims that the nearest competitor offers a 4 x 4-mm lead-frame module.

The integrated approach is "more cost-effective," said Jerry Miller, a product line director for CDMA and wideband-CDMA products at Anadigics. "You're still putting down the equivalent of two PA dice, but we only need about seven total components, compared with the competitors' 11. Those would generally be capacitors, maybe an inductor. The cost savings would be somewhere between 5 and 10 cents."

An alternative to using a dual-package module would be to use two dice, which are each generally around the same size as Anadigics' dual package. And indeed, many OEMs continue to use dual ICs, simply because they've gone that route in the past and don't want to lay out the board again, even if it results in a potential size and cost savings. You'd also want to avoid a dual-package module if you needed to support only one band, such as in the case of a similar phone that's designed for a Sprint PCS-only system, or if you were designing for an emerging market that supported only one cellular band. The best design practices put the 6314R PA near the transceiver, in this case a Qualcomm RFT6150. But there must put some space between the parts, since the SAW filters generally fit between the two. Each input to the PA must have a SAW filter between that input and the transceiver.

"From a layout perspective, designers must pay close attention to the PA subsystem. They must use good RF practices," said Miller. "This board is designed with components of different technologies and characteristics that have to be mixed and matched. It makes the whole RF section a little more difficult and design-intensive. On the baseband side, it's the software issues that can kill you."

I found it interesting that there's almost no shielding on this design. The shielding on competitive designs tries to isolate the RF radiation from getting into other parts of the phone. LG makes use of vias in the board as one way to minimize the RF radiation and thereby avoid the use of costly shielding.

Between the PA and PCS duplexer (UA622FM) are double rows of vias that are tightly spaced to minimize and contain the radiation. If the PA output, which is a relatively large signal, gets around the filter and out to the antenna switch at the output, you could have an isolation problem. The vias circumvent that problem, containing the radiation and making it conduct through the filter, instead of spraying all over the phone and radiating outward.

To eliminate a potential routing nightmare, Anadigics offers a similar power amp, the AWT6310, but with the pinouts reversed. This device works with the Qualcomm RFT6100 trans- ceiver, where the cellular and PCS outputs are reversed. The other difference is that the die for the cellular band is on top of the package and PCS I/O is on the bottom.

On the output side of the power amp lie the duplexers. Eventually, all those signals are routed to one antenna through a triplexer, which combines the cellular, PCS and GPS band signals going to the antenna. It's a common practice to use one antenna for all three bands, which is why the triplexer is popular.

Before the E911 mandates for pinpoint locators, you could use a simple antenna switch there, rather than the triplexer. However, that doesn't allow the user to receive location information while on a call. The next generation of the Anadigics power amplifier will integrate some of those switches as well as a voltage regulator.

Richard Nass ([email protected]) is editor in chief of Embedded Systems Design.