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Dual-baseband phone calls multiple standards

Posted: 28 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:LG SH-100 handset teardown? W-CDMA? HSDPA?

The LG SH-100 is a multitasking handset that can operate on an array of networking standards, including W-CDMA (UMTS)/HSDPA, GSM/GPRS/Edge (EGPRS), CDMA2000 1x and 1x EV-DO. The phone has a data rate of 1.8Mps.

The screen can slide upward to reveal a keypad for call dialing, as well as sideways to reveal a second numeric pad. Instead of having the numbers displayed in the typical format, there are two rows of five numbers. If the SH-100 had a QWERTY keypad like LG's F9100 phonewhich has been out for a while but which scored innovation points with its useful designI'd see the value in the slide feature. But since there are two numeric keypads, I am not sure how much benefit the sliding screen brings to the handset.

The phone has a decent feature set, including two cameras: a 1.3Mpixel version for image capture and a VGA camera for videoconferencing. Images display on a 2.2-inch QVGA 262k-color LCD screen, which flips from landscape to portrait view depending on the slide-out keypad. MP3 capabilities allow song storage on the 2Gbyte internal memory or on an external MicroSD card. Bluetooth and USB connectivity is supported. The phone measures 98-by-51.6-by-20.9mm and weighs 125g.

Two are better than one
From a component perspective, a few interesting design choices were implemented in the SH-100. The phone has two baseband processors. This is the first time Semiconductor Insights has seen such a configuration; we have encountered phones with multiple application processors but not multiple baseband devices.

The first baseband processor is the MSM6275, a member of Qualcomm Inc.'s Enhanced baseband family. The part supports W-CDMA (UMTS)/ HSDPA and GSM/GPRS/Edge networks. It has a data rate up to 1.8Mbps. The device supports the SH-100's videoconferencing functionality.

The second baseband processor is the MSM6500, which is part of Qualcomm's Multimedia baseband family. The processor supports CDMA2000 1x, 1xEV-DO and GSM/GPRS networks. It offers 1.3Mpixel resolution.

LG SH-100

A few interesting design choices were implemented in the SH-100 such as its two baseband processors.
(View LG SH-100's teardown diagram)

What might have been behind LG's decision to distribute the camera functionality between two baseband processors, and how did it arrive at the details of its partitioning scheme? The two devices have similar functionality, such as audio codecs, video codecs, image sensor interface, USB and Bluetooth connectivity and an SD card interface. But LG's rationale for assigning certain functions to one processor or the other defies easy explanation. For example, the MSM6500 supports data rates up to 2.4Mbps, but the LG phone taps the MSM6275's lower, 1.8Mbps data transfer. It may be that the data is transmitted on one of the networks that the MSM6500 does not support.

Similarly, the camera functionality of the MSM6275 can support up to 4Mpixels, but again here the SH-100 utilizes the MSM6500's lower, 1.3Mpixel support. This may be a design tradeoff between functionality and price, but given the rest of the features implemented, it is surprising.

Design factors
Having the different baseband processors operate on different networks requires a separate set of transmitters and receivers. While Qualcomm's RTR6250 transmitter and RFR6250 receiver are connected to the MSM6275, LG chose Skyworks' 74075 transmitter and 74675 receiver for CDMA networks connected to the MSM6550. In light of the large number of Qualcomm devices designed into the phone, choosing another source for two devices for which there were Qualcomm versions and reference designs available seems an odd decision.

The need for the two baseband processors to share information efficiently requires another component. The Cypress MoBL dual-port interconnect acts as a high-speed switch between the basebands, allowing independent, asynchronous access to both devices. The part's data throughput is an impressive 400Mbpsfast enough for both baseband processors to access information almost simultaneously from the memory. Typical connections of this type are performed through more traditional methods, such as UART, I?C and USB. But those connections are not fast enough for the latest HSxPA 3G speeds.

According to the Semiconductor Industry Association, there were 1 billion phones sold in 2006. It is estimated that 10-15 percent of those phones are smartphones that may use more than one processor. A device like the Cypress MoBL Dual-Port can be used as a bridge between processors in the near term until single-chip solutions are fully developed and widely available.

Single-chip processor solutions would move a cellphone into the midrange market. Phone developers would then begin to pursue additional functionality via multiple processors in the next round of high-end phone models.

- Gregory Quirk
Technical Analyst, Semiconductor Insights

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