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RF/Microwave??

Cellphone conquers elements

Posted: 19 Jul 2007 ?? ?Print Version ?Bookmark and Share

Keywords:ruggedized cellphone? Casio GizOne Type-V teardown? dual-band CDMA?

As every cellphone user knows, the more you use your mobile, the more likely it will suffer physical trauma. Pull it out to grab a call and a slip of the hand sends it tumbling. Take a phone near a lake and it will be among the first to seek out the water. Mobility and morbidity seem closely linked.

Enter the Casio GizOne Type-V, a ruggedized clamshell-style cellphone for Verizon's CDMA network. The GizOne claims to have passed military specification (Mil-spec) tests for shock and moisture resistance, building on Casio's long and successful line of stout G-Shock watches. The GizOne was initially introduced to the Japan market in 2005 and enjoyed great popularity. The recent U.S. launch suggests that the demand for a robust design is global.

Modern, robust design
A fish aquarium demo of the GizOne family earlier this year at the Consumer Electronics Show caught my eye. Casio's marketing folks figured a live functional phone submerged with a group of goldfish would make its point. I was curious to see how Casio had equipped the phone to endure hours in the tank.

Beyond its water and humidity resistance, the design is claimed to have survived multipass drop tests from 1.5m, two days' exposure to saltwater fog, vibration tests and dust-resistance tests consistent with MIL-STD-810F. We didn't verify the claims, but a read of the spec certainly bolsters the notion that the tests are a decent proxy for the abuse an average user might heap on a cellphone.

While the GizOne promotes tool-like toughness, it still offers a modern feature set. A 2Mpixel camera with LED flash (doubling as a flashlight) joins up with two displays: a 262,144-color, QVGA, 240 x 320pixels, TFT-LCD unit inside and a monochrome, 100 x 100pixels, STN display outside. The GizOne also supports Verizon's Vcast application suite and video service, along with Assisted GPS (A-GPS) location technology, picture and ringer ID, 72 polyphonic ringtones, 1xEvDO data, an Openwave microbrowser, messaging, predictive text entry and Brew (Binary Runtime Environment for Wireless) applications. Casio claims the 3.7V, 1,050?A-hr battery delivers up to 3.2hrs of talk time and 400hrs of standby time.

The dual-band CDMA (850/1,900-MHz) communications capability relies on a Qualcomm chip set centered on the company's MSM6550 baseband. MSM6550 is a two-chip package that splits analog and digital baseband duties into separate dice whose process technologies can be optimized for their respective functions.

The radio transceiver path is also split up, this time into separately packaged chips. Given the always-on nature of CDMA's frequency-division protocol, Qualcomm thus far has chosen to let the physical isolation of chips address the electrical isolation of potentially interfering signals.

Casio GizOne Type-V

The Casio GizOne Type-V is a ruggedized clamshell-style cellphone that is said to have passed military specification tests for shock and moisture resistance.
(View Casio GizOne Type-V's teardown diagram)

On the radio front-end, an RFMD RF5144 dual-band RF power amp (transmit) and Qualcomm RFL6000 low-noise amp (receive) join to an interesting "quintplexer" from Avago. The ACFM-7101 combines two duplexers, for isolating the receive and transmit portions of each CDMA band, along with handling signals associated with the GizOne's A-GPS function. The internal filters rely on Avago's film bulk acoustic resonator technology, an alternative to the widely used surface-acoustic-wave devices visible in other parts of the GizOne's radio implementation. Casio opted for a Matsushita/Panasonic AN32110A power management ASIC over Qualcomm's often-seen PM6650 alternative.

Built for toughness
Using underfill for the larger chips' BGA packages helps with shock resistance. The same anchoring of large BGAs is often seen in more-conventional phones, where even basic temperature cycling and moderate PCB flexure can put solder joints at risk.

Moving out to the toughened-up enclosure design, the most visible addition is a bumper-car style fender at the phone's end. Elsewhere, moisture and dust seals are the order of the day. Any button, electrical interface, latch or audio transducer represents a point for incursion of moisture and grime, and it is in those areas that the GizOne Type-V has focused most on special design features.

The machined battery door latch is a spinning catch, so that an O-ring seal can be employed in the feedthrough for the latch mechanicals. An O-ring seal holds up well in a rotating-axle pass-through; the design closely parallels that of the function buttons found on water-resistant watches and chronographs.

Similarly, a static O-ring serves as the seal for the headset/charging jack cover, which snaps into place, keeping electrical internals out of harm's way.

A large gasket is found between the mating surfaces of the upper flip's two enclosure halves, made of plastic and metal and clamped together with the help of machine screw fasteners. In the lower half of the flip enclosure, the keypad mat provides an integral seal. The keypad's silicone rubber carrier film is oversized to extend all the way to the lower case half's edge. Elastomer carrier films used for the side keys of the GizOne are pinched at assembly time to provide seals at the exit point for the other buttons of the enclosure.

The electrical cable connecting the lower and upper halves relies on a rubber-grommeted feedthrough in the hinge. The polyimide flex cable is water-resistant by design, so only the points of entry and exit from the case represent critical areas for sealing.

The speakerphone, earpiece and microphone are the last elements of case sealing, with a thin secondary membrane adhesively attached to the inside of the case in the areas of the acoustic ports. The membrane covers each of the transducers while allowing sound energy to propagate through. The clamping pressure of the enclosure assembly is critical to holding the seal of the rubber-booted acoustic components against the isolating membranes.

Extra hardware for ruggedness comes at a price, with handset weight coming in at 151.5g. Overall, it is the mechanical design of the GizOne Type-V that distinguishes the phone from an array of alternatives. Whether ruggedness or style is the focus, enclosure design is the increasingly important handset differentiator.

- David Carey
President, Portelligent




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