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3.3 Transceiver Module (AD6548)
Figure.3-3-1 AD6548 FUNCTIONAL BLOCK DIAGRAM
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 supply
voltages to the functions on chip, with a battery input voltage of between 2.9V and 5.5V. Comprehensive
power down options are included to minimize power consumption in normal use.
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