BOM shrinks handset costs

Reducing the handset bill of materials can be a chip designer's nightmare, involving further integration of the various radio, baseband and audio functions to reduce chip count. By comparing the silicon solutions developed by Infineon for the Panasonic EB-MX6 handset and the new PMB7870 E- GOLDradio, one can see the cost savings and system simplification achievable with the more highly integrated solution. This article will also review some key aspects of the PMB7870 E-GOLDradio.

Most notably, Infineon's recently released PMB7870 E-GOLDradio incorporates the baseband and RF functions into a single die, replacing the multicomponent solution in previous systems.

In the EB-MX6 handset, nine major semiconductor devices enable voice (GSM 900/1800/1900) and enhanced multimedia features, such as music, Web and text messaging. The triband handset also sports a 1.3-megapixel camera, a speakerphone and a 2.2-inch TFT color screen with 320 x 240 QVGA resolution.

When examining the Panasonic EB-MX6 against the E-GOLDradio, we start by adding the die area from the Infineon PMB8875 S-GOLDlite baseband and PMB6270 SMARTi SD transceiver ICs (40.95 mm² and 4.41 mm², respectively) to come up with a total of 45.36 mm². In contrast, for the PMB7870 E-GOLDradio, Infineon integrated the functionality of similar baseband and RF components on a single die with a total size of 32.45 mm², for an approximate die area savings of 12.91 mm².

Since we are comparing dice (and, later, packages) whose designs are similar but not identical, we should note the main design differences between the integrated PMB7870 E-GOLDradio and the separate devices used in the EB-MX6 handset (the PMB8875 S-GOLDlite baseband and PMB6270 SMARTi SD transceiver).

The PMB7870 E-GOLDradio integrates the PMB7860 E-GOLDlite baseband and PMB6271 SMARTi SD2 transceiver. The PMB8875 S-GOLDlite baseband is geared more toward more feature-rich multimedia handsets, whereas the PMB7860 is a stripped-down feature set optimized for entry-level, low-cost phones, with little beyond the basics for baseband communications.

While the PMB7870 E-GOLDradio skimps on the baseband side to accommodate low-cost handsets, it has added some features from an RF perspective. Comparing the PMB6270 SMARTi SD with the PMB6271 SMARTi SD2, it is clear that Infineon has optimized the SD2 for cost and functionality by integrating a fully digital, digitally controlled crystal oscillator.

The die size alone does not tell the entire story, and, therefore, it is worthwhile looking at the overall package size. Within the Panasonic EB-MX6 handset, the Infineon PMB8875 has a package size of 121 mm^2, and the PMB6270 has a package size of 49 mm², resulting in a total area of 170 mm². The Infineon PMB7870 E-GOLDradio has a package size of 81 mm², for a savings of about 50 percent of the board area required by the two-chip solution. The integration and optimization of the baseband and RF ICs reduce the total package area, and that directly translates into smaller real estate area on the board--and, therefore, lower cost.

Taking matters a step further, if we compare the package sizes of the individual ICs that make up the PMB7870 E-GOLDradio, the PMB7860 baseband package measures 64 mm², while the PMB6271 transceiver package measures 25 mm². Combined, the package area is 88.75 mm², or approximately 7.75 mm² more than the E-GOLDradio integrated solution.