Samsung SGH-2488 service manual.pdf

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DUAL BAND Mobile
Cellular Phone
SGH-2488
SERVICE
DUAL BAND Mobile Cellular Phone
Manual
CONTENTS
1. Exploded Views and Parts List
2. Electrical Parts List
3. Block Diagrams
4. PCB Diagrams
5. Schematic Diagrams
1
4
GHI
7
PQRS
2
ABC
5
JKL
8
TUV
0
3
DEF
6
MNO
9
WXYZ
ELECTRONICS
Samsung Electronics Co.,Ltd.
Printed in Korea
11/1999 Rev 1.0
GH68-00844A
1. General Description
1-1 Dualband System
1-1-1 Calls
Dual band handsets supports the E-GSM and DCS system, DCS is an acronym for Digital Cellular system, and
GSM
¨
is an acronym for Global System for Mobile communications
©
, using TDMA for wide-area cellular
operation. The GSM and DCS system consists of the sub-systems shown;
The Mobile Station (MS) talks to the Base Station System (BSS) via an RF air interface. The Base Station System
(BSS) consists of Base Transceiver Station (BTS) and a Base Station Controller (BSC). The interface between BTS
and BSC is called an Abis interface. Generally one BSC controls 20 to 30 BTSs, and a Mobile Switching Center
(MSC) controlling the traffic among different cells would be reported back from a number of BSSs. A Visitor
Location Register (VLR) will be allocated to one MSC to find the mobiles out of their home cell by listing them
to VLR. The MSC would also be connected to the Home Location Register (HLR), the Authentication Center
(AC) and the Equipment Identity Register (EIR) So the system verify that the users and equipment are legal
subscriber.
1-1-2 Channels
Channels used in the E-GSM and DCS system can be divided into two classes - Logical and Physical channel.
Physical channels can be described in terms of their frequency and time domain characteristics. They are the
actual frequencies and timeslots the MS and BS transmits or receives on. The logical channels are mapped onto
these physical channels logically. Any particular and instant, physical channels may be control or traffic
channels, which determines the function of a physical channel at a particular point in time.
1-1-3 Airinterface of ARFCN (Absolute Radio Frequency Channel Number)
975
880.2 MHz
1023
0
1
890.2 MHz
2
3
...
...
...
...
123
124
914.8 MHz
E-GSM: TX: Ful(n) = 890MHz + (0.2MHz) • n, 0≤n≤124 and
Ful(n) = 890MHz + (0.2MHz) • (n-1024), 975≤n≤1023
975
925.2 MHz
1023
0
1
935.2 MHz
2
3
...
...
...
...
123
124
959.8 MHz
E-GSM: RX: Fdl(n) = Ful(n) + 45MHz
512
1710.2 MHz
885
DCS Tx: Ful(n) = 1710MHz + (0.2MHz) • (n-511)
n = ARFCN,
512≤n≤885
1784.8 MHz
512
1805.2 MHz
885
DCS Rx: Fdl(n) = Ful(n) + 95MHz
< Fig. 1 ARFCN Diagram >
1879.8 MHz
Samsung Electronics
1-1
General Description
1-1-4 GSM TDMA Timeslots, Frames, and Multiframes
TCH
Multiframe
0
1
2
3
4
...
...
...
...
...
...
24
25
BCH
Multiframe
0
1
2
3
4
...
...
...
...
...
...
49
50
TDMA
Frame
0
1
2
3
4
5
6
7
Timeslot
T
Information
F
Midamble
F
Information
T
Guard
< Fig. 2 Concept of Frames and Timeslots >
1-1-5 Logical Channel
TCH (Traffic CH) is used mainly for transferring the speech information, and the BCH (Broadcast CH) is
related to control information.The major function of BCH is transferring information on the downlink for MS
synchronization, identification, paging, and controll. BCH is always radiated from every cells and the MS tries
to find the BCH which has highest level soon after turned on. The organization of BCH is shown belows;
FCCH (Frequency Correction Channel), SCH (Synchronization Channel), and BCCH (Broadcast Control
Channel). CCCH (Common Control Channel) will play a role like a message board, and is divided into two
control channels - PCH (Paging Channel) and AGCH (Access Grant Channel). SACCH (Slow Associated
Control Channel) exists every 12 frames, controlling and controls the TX power level and timing advance of
MS, transferring cell information to MS on downlink, transferring the information about RX level, Quality, and
RX level of adjacent cell on uplink. FACCH (Fast Associated Control Channel) steals and changes the TCH
when needing a Handover. SDCCH (Stand-alone Dedicated Control Channel) and RACH (Random Access
Channel) operate during the call setup procedure.
1-2
Samsung Electronics
2. Circuit Description
2-1 RF Part
2-1-1 Frequency Generator
The 13MHz reference clock (VCTCXO) drives the logic and RF part. The 13 MHz reference is controlled by the
logic (10bits DAC minimum) and is kept to a frequency error less than ±0.1 ppm after synchronization with the
GSM network.
The IF VCO generates 233~259.5MHz VHF LO used in the RX I,Q Demodulator and after
doubling(493~519MHz), it used in the TX I,Q modulator. The UHF LO for the first RX down conversion and
the TX offset mixing works in superheterodyne mode to reduce the relative bandwidth and to be able to work
at a frequency greater than 1 GHz.
2-1-2 Transmitter
The baseband GSM chipset (Kernel 5) generates I and Q baseband signals for the transmit modulator. The
modulator (U2893B) is the first stage which takes the baseband signal and upconverts it to a fixed intermediate
frequency. The modulator provides more than 35dBc of carrier and unwanted side-band refection and produces
GMSK modulated signal, the ÒreferenceÓ signal at 493~519 MHz which passes to the offset phase-locked loop
block (OPLL). The OPLL consists of a down-converter, phase detector, loop filter and transmit VCOs operation
at the final RF output frequency. The down converter mixes the UHF LO (eg. 1210MHz) with the transmit VCO
signal to generate a ÒfeedbackÓ signal at 493~519 MHz. The ÒfeedbackÓ signal passes via a limiter to one port
of the phase detector. The GMSK ÒreferenceÓ signal from the modulator passes via second limiter to the other
input port of the phase detector. The phase detector generates an error current proportional to the phase
difference between the ÒfeedbackÓ signal from the down-converter and the ÒreferenceÓ signal from the
modulator. This error current is filtered by a third order low-pass filter to generate an output voltage which
depends on the GMSK modulation and the desired channel frequency. This voltage controls the transmit VCO
such that the VCO output signal, centered on the correct RF channel, is frequency modulated with the original
GMSK data. The center frequency of the transmit VCO is offset from the UHF LO frequency by 493~519MHz.
The OPLL acts as a tracking narrowband band pass filter tuned to the desired channel frequency. This reduces
the wideband products. The OPLL architecture results in a low-noise GMSK modulated signal at
902MHz(1747MHz) with very low spurious content.
The RF GMSK output from the transmit VCO is fed to the RF power amplifier. The peak output power and the
profile of the transmitted burst are controlled by means of a closed feedback loop. The RF output from the PA is
sampled with a directional coupler. The sampled signal passes to an RF detector diode whose output voltage is
dependent on the incident RF level. This ÒfeedbackÓ voltage passes to the inverting input of the loop integrator.
A ÒreferenceÓ signal is generated within the baseband section under control of the layer 1 software. The loop
maintains zero difference between the ÒfeedbackÓ signal and the ÒreferenceÓ signal. In this way, the amplitude
and shape of the transmitted RF burst may be controlled by the baseband processor. In particular, the rise and
fall profiles can be controlled to meet the stringent power/time templates and switching transient requirements
of GSM 05.05.
The RF output passes to the antenna connector via an integrated TX/RX switch and lowpass filter to attenuate
the harmonics generated by the power amplifier.
Samsung Electronics
2-1

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