Design Considerations
A Wireless Data Access Card is networking equipment for portable devices allowing the user to connect to the internet via an available USB port or PCMCIA card slot.
The data flow begins with a signal entering the processor. Such application requires chipset with fast CPU processing for smooth user interface as provided by TI’s LoCosto family of single chip solutions. Benefits include smaller board space, reduced power consumption and reduced system cost. The chipset supports various dual band frequencies: 850/1900, 900/1800, 850/1800 or 900/1900 thereby supporting worldwide roaming. Enhanced capabilities include mass storage (SD/MMC, micro memory stick, micro-SD) support, USB interface, and GPS connectivity. GPS can provide support for location based services like mapping, weather information and traffic details. Full duplex data and voice communication can facilitate the use of data card as a phone without deferring internet access.
Housekeeping processes like the control of the Power Amplifier or LNA, RTC, LED control, etc. can be outsourced to TI’s ultra low power MSP430 microprocessor platform.
The RF module features high speed digital to analog converter DAC5652A which offers exceptional dynamic performance, tight-gain, data rate up to 275MSPS and offset matching characteristics that makes it suitable for direct IF communication applications. The quadrature modulator combines amplitude and phase modulation allowing more data to be transmitted over the same bandwidth and eliminates intermodulation interference by suppressing the carrier. TI’s TRF3703 is a low-noise direct quadrature modulator; ideal for high-performance direct RF modulation from 400 MHz up to 4 GHz. Use of such double balanced mixer mitigates the strict selection criteria for data converters. High bandwidth sample and hold ADC like ADS5237 minimizes even-order harmonics and gives excellent common-mode noise immunity. TI’s TRF3761 family includes low noise integer N PLL frequency synthesizer with integrated VCO to provide spur free output. The need to support multiple frequencies with the same device is supported by TI’s family of 4-PLL VCXO Clock Synthesizers like CDCE949 for the chipset. ADC, DAC and DDC/DUC requires ultra low jitter clock like CDCE62005 to get error free data.
TI features highly integrated devices with low external component counts and small lead-free packaging to provide the smallest power management solutions for wireless application. For high end data access card, integrated solution for processor power such as TWL3029 power management unit can be used. As extra functionalities such as RTC Control, Amplifier gain control, and glue logic have been integrated onto the same board, low cost Buck or Boost Converters such as TPS62250 or LDOs like TPS79918 have been included for additional power rails.
EmoticonEmoticon