Garmin's GPSMAP-76S: Location, location, location

The majority of the 76S' electronics resides on a single four-layer mainboard. Central to the design are a TI-manufactured Garmin baseband DSP/controller ASIC and a Garmin single-chip GPS receiver radio IC. System memory consists of a 32-Mbyte flash chip from Samsung for mapping data, 2 Mbytes of AMD flash for op code and 512 kbytes of Samsung SRAM for working memory. Linked to the central baseband chip are the radio IC and independent sensors for heading/elevation. To determine altitude, the 76S uses a MEMS-based barometric sensor. The Intersema MS5534A module sports a piezoresistive bridge whose properties shift under pressure-induced deflection of a "drumhead" silicon membrane; a companion CMOS chip for A/D conversion, and host interface is also integrated. Directional compass data is derived from a Honeywell HMC-1022 dual-sensor package containing magnetoresistive thin-film bridges-one IC for "north-south," the other for "east-west." An external Cirrus Logic A/D converter links the Honeywell sensors to the DSP/controller.

Other key assemblies are the quadrifilar antenna, keypad board and display assembly. The internal antenna is implemented with carefully crafted conductors patterned in spiral fashion around a tubular low-loss RF laminate. An external antenna connector is also present, with the system detecting and selecting antenna source via a RF switch. A 3-volt, dual-AA battery source powers all system electronics through spring contacts to the gasketed keypad board, which in turn is linked to the mainboard and display via ribbon cable. The mainboard also interfaces through spring contacts to a sealed external serial-port connector for map data download via PC. The high-resolution monochrome LCD provides detailed data and graphics readout, and is located behind a clear plastic upper enclosure. The ruggedized and watertight construction come at a price, however, with enclosures contributing 46 percent of the total product weight-a hefty addition by handheld standards.

Cost-of-goods-sold analysis points to a manufacturing cost below $100, a fraction of the 76S' $400 street price. Low cost combined with the modest levels of integration suggests room for further miniaturization-an open opportunity to embed the multidimensional location technology in an expanding range of host appliances.

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DAVID CAREY IS CEO OF PORTELLIGENT (AUSTIN, TEXAS; WWW.PORTELLIGENT.COM), WHICH DOES TEARDOWN REPORTS ON PORTABLE ELECTRONIC SYSTEMS.