K850
1203-2528 rev. 1
FUNCTIONAL OVERVIEW
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RF System Control
The access subsystem of the digital baseband controller controls the overall radio system. In
both EDGE/GSM/GPRS and WCDMA air interface mode, the digital baseband controller controls
the radio system through a 3-wire serial bus.
The digital baseband controller also manages PA band control and the antenna switch
mechanism in the front end module. The 26 MHz VCXO clock residing in the GSM/EDGE
transceiver is turned on only when required. The digital baseband controller initiates turning on
of the clock. The EDGE/GSM/GPRS RF system requires control, which is temperature dependent.
The temperature within the RF system is estimated by a voltage measurement performed by
the analog baseband controller N2000 (Vera).
The control flow for the RF system.
Radio Part
Antenna
The mobile system antenna interface connects the Wideband Code Division Multiple Access
(WCDMA) and Global System for Mobile Communication (GSM) input/output to the antenna of
the Mobile Phone. It is a bi-directional RF interface containing signals in the range 800 MHz to
2.2 GHz. The mobile system antenna interface is the interface between the Mobile Phone Radio
Frequency (RF) input/output and the mobile system antenna. The interface handles the GSM
850, EGSM 900, GSM 1800, GSM 1900, and WCDMA band I, II and V RF inputs/outputs.
Mobile System Antenna Interface:
Radio Modules
GSM/GPRS/EDGE Radio Module
N1200 (Thor)
The Front End module block connects the proper block in the radio system to the antenna. The
Front End module has two inputs for GSM/GPRS/EDGE, one for low band and one for high band.
The GSM/GPRS/EDGE power amplifier output is filtered by the low pass filter in the Front End
module and then connected to the antenna through a switch and diplexer. In receive mode, the
GSM/GPRS/EDGE signal from the antenna passes through the diplexer and switch to one of the
four internal receive SAW filters. The SAW filter provides receive band selectivity and converts
the unbalanced receive signal to a differential signal required by the GSM/GPRS/EDGE receiver.
In GSM/GPRS/EDGE systems, transmit and receive operations are divided in time and the
switch connects the proper block in accordance with the mode of operation that is, transmit or
receive: one at a time in the GSM, DCS, and PCS bands. The module is shielded using fence
and lid technology. The main components contained are transceiver ASIC, PA module, Front
End Module and X-tal.
Frequency Generation
The 26 MHz reference signal is used as the reference for the on-chip synthesizer. To cover the
required frequency range, the integrated Voltage Controlled Oscillator (VCO) operates at twice
the frequency for band 1800/1900, and at four times the desired frequency for band 850/900.
GSM/GPRS/EDGE Transceiver
The GSM/GPRS/EDGE transceiver use a digital interface that is shared between receive
and transmit data. The receive interface is based on I and Q data and the transmitter interface
is based on envelope and frequency data. The quad band GSM/GPRS/EDGE transceiver has the
following general features:
Individual low-noise amplifiers for the 850, 900, 1800 and 1900 MHz frequency bands with
a common quadrature mixer
Fully integrated VCO with dividers to generate both receive and transmit frequencies
I and Q baseband receive channel amplifiers with on-chip antialiasing filtering
I and Q receiver sigma-delta A to D converters
Digital interface for the receive I and Q channel
Multi modulus prescaler for direct VCO modulation in transmit mode
Integrated phase detector with programmable charge pump
Transmit output buffer with controllable output power level
Transmit baluns integrated
Digital interface for the transmit frequency and amplitude modulation
3-wire serial bus interface for control, configuration, and test
Deep power down function
Programmable power level to power amplifier (PA)
Technical Description
SEMC Troubleshooting Manual
67
(101)
