Starting at the baseband, the Mediatek AD6903 puts two slices of silicon on one package. The larger one is likely a Blackfin-based DSP supporting communications processing for both GSM and TD-SCDMA. The second, smaller chip would, by process of elimination, contain the ARM9 controller core and other digital aspects of the system, such as USB and memory interface. In that vein, the part is directly supported by a Numonyx (formerly Intel--so many name changes!) two-chip memory stack with 64 Mbytes of NOR flash and 16 Mbytes of pseudo-SRAM, along with a user-upgradable MicroSD card slot.
For the primary analog functions, the single-chip AD6857 takes care of both standards' analog/digital interfaces between radios and digital basebands, along with power management and much of the audio subsystem.
Moving on to the radio, the duality of design becomes more apparent. Essentially, there is a dedicated transceiver for GSM in the AD6549, with an RF Micro Devices RF3166 RF power amp completing the GSM signal chain. TD-SCDMA requires a separate radio component set and splits the transmit and receive paths into separate devices. As with CDMA and W-CDMA devices early on, the challenges of spread-spectrum design have prevented monolithic integration of uplink and downlink radio traffic. The AD6541 handles transmit modulation, while the AD6547 tackles receive downconversion. The former part is followed by an RF isolator and Skyworks' SKY77161 TD-SCDMA RF power amp.
Both radio chips are based on a direct-conversion architecture and contain on-chip voltage-controlled oscillators, filters and localized power regulation to keep external component count low as an offset to the two-chip implementation. A Murata-manufactured RF front end is responsible for all the mode and time-division switching associated with both protocols, serving as the RF signal traffic cop between the radio subsystems and antenna.
Other devices support audio output (AKM AK4642), Bluetooth (CSR BC41B143A-BluCore4) and touchscreen control (AKM AK4183). The MV8602 media processor from MtekVision offloads imaging-related tasks stemming from the T68 phone's 1.3-Mpixel camera and functions as the LCD interface.
TD-SCDMA may have Eastern roots, but the independence sought with the standard has yet to be fully realized. That may change now that China's Spreadtrum is getting into the TD-SCDMA processor game. In the spirit of that competition, let the (other) games begin!
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David Carey is president of Portelligent (www.teardown.com), a TechInsights company. The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics.