Sony Ericsson C702 Troubleshooting Manual page 91

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 duplexer. In receive mode,
the GSM/GPRS/EDGE signal from the antenna passes through the duplexer 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:
The GSM/EDGE transceiver has the following 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)
FUNCTIONAL OVERVIEW Technical Description
Block diagram of the GSM/EDGE Transceiver:
Transmitter
The transmitter block consists of the following sub-blocks:
A separate block is used to convert the digital bit streams from the baseband into parallel
words to be used in the DAC and the Sigma Delta modulator. This block also includes
programmable delays for optimizing delays between the different modulation paths. The
combined DAC and LP-filter is used to convert the digital words of the digital block into analog
signals. The second FM-path is used to add the high frequency part of the FM to the VCO. It
also includes an auto-tuning block that compensates VCO gain variations. The AM-block
converts the differential voltage from the DAC to a single-ended output that drives the PA. The
output is scaled according to the desired output power, and an offset can be added for PA
linearization. The TX-buffer is used to drive the PA with the correct power level. A divide by 2 or
4 block is used to generate the correct output frequency from the 4 GHz VCO.
TX Frequency, Channel and Power Level Range:
GSM 850:
Frequency Range: 824,2 MHZ – 848,8 MHZ
Channel Range: 128 – 251
Power Level: Min 19 – Max 5
SEMC Troubleshooting Manual
C702
1221-7857 rev. 1 91 (115)