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3.3
Transceiver Module (AD6548)
3.3.1 General Descriptions
The AD6548/9 provides a highly integrated direct conversion radio solution that combines, on a
single chip, all radio and power management functions necessary to build the most compact
GSM radio solution possible. The only external components required for a complete radio design
are the Rx SAWs, PA, Switchplexer and a few passives enabling an extremely small
cost effective GSM Radio solution.
The AD6548/9 uses the industry proven direct conversion receiver architecture of the
OthelloTM family. For Quad band applications the front end features four fully integrated
programmable gain differential LNAs. The RF is then downconverted by quadrature mixers and
then fed to the baseband programmable-gain amplifiers and active filters for channel selection.
The Receiver output pins can be directly connected to the baseband analog processor. The
Receive path features automatic calibration and tracking to remove DC offsets.
The transmitter features a translation-loop architecture for directly modulating baseband
signals onto the integrated TX VCO. The translation-loop modulator and TX VCO are extremely
low noise removing the need for external SAW filters prior to the PA.
The AD6548/9 uses a single integrated LO VCO for both the receive and the transmit circuits.
The synthesizer lock times are optimized for GPRS applications up to and including class 12.
To dramatically reduce the BOM both TX Translational loop and main PLL Loop Filters are fully
integrated into the device.
AD6548 incorporates a complete reference crystal calibration system. This allows the external
VCTCXO to be replaced with a low cost crystal. No other external components are required. The
AD6549 uses the traditional VCTCXO reference source.
The AD6548/9 also contains on-chip low dropout voltage regulators (LDOs) to deliver regulated
Figure.3-3-1 AD6548 FUNCTIONAL BLOCK DIAGRAM
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