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3G phone springs from 2G design overhaul

Posted: 02 Dec 2009 ?? ?Print Version ?Bookmark and Share

Keywords:Samsung SGH-J750 teardown? 3G? W-CDMA?

The J750 borrows from a slider form-factor appearing in earlier Samsung designs. (Click on image to view teardown.)

Released in Q1 08, Samsung's SGH-J750 tells a less-fleeting tale of OEM sourcing decisions, ASIC development strategies and foot-in-the-door approaches behind the cellphone market.

Starting with the design itself, the J750 borrows from a slider form-factor appearing in earlier Samsung designs. Unlike the earlier, similar 2G predecessors, however, the J750 provides 3G (W-CDMA) connectivity in the 2,100MHz band along with quad-band GSM/Edge. With a 1.8-inch 176 x 220 LCD and 1.3Mpixel/QCIF dual-camera design, the J750 certainly wasn't positioned as a high-end device. Still, media playback, Bluetooth, Java support, speakerphone and host of other features make for a somewhat up-market 3G product in the launch timeframe.

The slider design makes for complicated enclosures so the J750 mechanicals were opportunistically borrowed from earlier designs, lowering production and tooling costs for the new 3G model. Along with two keyboards and roughly twice the plastic moldings of a bar-format phone, the slider form-factor requires a rather sophisticated "endoskeleton" supporting both articulated movement and moving electrical connection between lower and upper halves. The combination of more complex plastics and metal/plastic composites for enclosures no doubt figured in the significant reuse of earlier tooling. Primarily, Samsung did an internal overhaul to bring 3G capability to a formerly 2G industrial design, saving development time (cost) along the way.

Electronics for the J750 reside mostly on the buildup microvia circuit board shown in this writeup, an assembly located in the lower slider half that also supports the larger numeric keypad. A second board in upper slider provides almost exclusively for display and camera connections via a flex cable to the main board in the lower half. A smaller navigation keypad used with the phone in closed form is also designed into the simpler upper PCB.

Notable for us along with the recycled industrial design was the chipset chosen by Samsung. As a long-time user of Qualcomm chipsets for 3G handsets, Samsung surprised us in the J750 with the choice of Broadcom's first-generation 3G CellAirity platform. A trio of parts defines Broadcom's cellular contributions, filling sockets for baseband and power management with the BCM2133, BCM2141 and BCM59001 respectively. The BCM21xx pair creates the dual-mode (GSM and W-CDMA) baseband function while the BCM59001 handles power and other analog system functions. Bluetooth also comes from a Broadcom chip and supporting memory is a Samsung stacked-die package providing 32Mbyte each of NOR, OneNAND and p-SRAM.

The somewhat rogue design win for Broadcom with Samsung was not the only standoutBroadcom's choice of a twin-component baseband for 3G was also noteworthy. The BCM2133 was a part we'd encountered in 2007 with GSM-only teardowns. Now with the J750 we found it paired to a second co-processor for W-CDMA. The logical conclusion was Broadcom's technical approach of incrementalism, where the 2G chip design investment was preserved and supplemented with a bolt-on component to achieve 3G. Clean-sheet ASIC development was put aside in favor of a time-to-market enhancing approach of add-on, with a further benefit being continuity of chips for 2G-only customers.

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