The radio part of the SX1, is using a Hitachi
The radio part is designed for Tripple Band operation, covering EGSM900, GSM1800 as well as GSM
1900 frequencies, and can be divided into 4 Blocks.
-Power supply for RF-Part
-Transmitter
-Receiver
-Synthesizer,
The RF-Part has it´s own power supply realised by a voltage regulator which is located
inside the ASIC. The voltages for the logic part are generated by the Power-Supply ASIC too.
The transmitter part converts the I/Q base band signals supplied by the logic (EGOLD+) into RF-
signals with characteristics as defined in the GSM recommendation (
by a power Amplifier the signal is radiated via the internal or external antenna.
The receiver part converts the received GMSK signal supplied by the antenna into IQ base band
signals which are further processed by the logic (EGOLD+).
The synthesizer generates the required frequencies for the transmitter and receiver. A 26MHz
oscillator is acting as a reference frequency.
Restrictions:
The mobile phone can never transmit and receive in both bands simultaneously. Only the monitor time
slot can be selected independently of the frequency band. Transmitter and receiver can of course
never operated simultaneously.
The voltage regulator for the RF-part is located inside the ASIC D2802. It generates the required 2,8V
“RF-Voltages” named VCC2_8 and VCC_SYN .The voltage regulator is activated as well as
deactivated via M_RF1_EN
EGOLD+. The temporary deactivation is used to extend the stand by time.
Circuit diagram
(TDMA-Timer H16)and VCXOEN_UC (Miscellaneous R6)provided by the
CC2_8
SYN
4.2 Frequency generation
4.2.1 Synthesizer: The discrete VCXO (26MHz)
The SX1 mobile is using a reference frequency of 26MHz for the Hitachi chip set. The generation of
the 26MHz signal is done via a TVCXO Z950. TP (test point) of the 26MHz signal is the TP 2310
The oscillator output signal 26MHz_RF is directly connected to the BRIGHT IC (pin 38) to be used as
reference frequency inside the Bright (PLL). The signal leaves the Bright IC as BB_SIN26M at (pin 36)
to be further used from
the EGOLD+ (D100
Bright 4
To compensate frequency drifts (e.g. caused by temperature) the oscillator frequency is controlled by
the (AFC) signal, generated through the internal EGOLD+ (D100
diode V951. Reference for the “EGOLD-PLL” is the base station frequency. To compensate a
temperature caused frequency drift, the temperature-depending resistor R959 is placed near the
VCXO to measure the temperature. The measurement result TVCXO is reported to the
EGOLD+
The required voltage VCC_SYN is provided by the ASCI D2820
(Analog Interface P3) via R138 as the signal TENV.
The first local oscillator is needed to generate frequencies which enables the transceiver IC to
demodulate the receiver signal and to perform the channel selection in the TX part. To do so, a control
voltage for the LO1 is used. Gained by a comparator. (located inside the Transceiver (Bright -IC)).
This control voltage is a result of the comparison of the divided LO1 and the 26MHz reference Signal.
The division ratio of the dividers is programmed by the EGOLD+, according to the network channel
requirements.
The first local oscillator (LO1) consists of the PLL inside the Bright(D800), an external loop filter and
the VCO (Z850) module. LO1 generates frequencies from:
3700-3980 MHz for EGSM900
3580-3760 MHz for GSM1800
3860-3980 MHz for GSM1900
The VCO (Z850) is switched on by the EGOLD+ signal PLLON (TDMA-Timer F16) via V850 and therefore
supplied with VCC2_8. The VCO guarantees by using the control voltage at pin5 a coverage of the
EGSM900, GSM1800 and GSM1900 frequency band and frequency stability. The Bright gained
control voltage passes on the way to the VCO a discreet loop filter (typical value from 0,5 – 2,1V).
The channel programming of the PLL happens via the EGOLD+ signals RFDATA; RFCLK; RFSTR.
(RF Control J15, J16, J17). If the Bright IC gets via the same signals a GSM1800 channel information, the
VCO is switched to this frequency by Pin 42 Bright (Pin 3 VCO).
For GSM900 - RX = “low signal” for channel 975-49
= “high signal” for channel 50-124
- TX = “high signal” for all channels
For GSM1800 - RX = “low signal” for all channels
- TX = “low signal” for all channels
For GSM1900 - RX = “high signal” for all channels
- TX = “high signal” for all channels
The VCO output signal passes the “Balun” transformer (Z851) with insertion losses of ~ 2dB to arrive
at the Bright IC.
The required voltage VCC8_8 is provided by the ASIC D2820
Circuit diagram
The second local oscillator is required for transmitter operations only. It consists of a PLL and a VCO
which are integrated inside the Bright 4, and an external second order loopfilter (R831; C830; C832).
Before the VCO generated 640 or 656MHz signal arrives at the modulator, it is divided by 8. So the
resulting frequency after the IQ modulator is 80/82MHz (depending on channel and band).
Programming of the LO2 PLL is done in the same way as described at the LO1. The tree-wire-bus
(EGOLD+ signals RFDATA; RFCLK; RFSTR.
stability, the 640MHz VCO signal is compared by the phase detector of the 2
reference signal. The resulting control signal passes the external loop filter and is used to control the
640/656MHz VCO.
The required voltage VCC_SYN is provided by the ASIC D2820
Circuit diagram
(RF Control J15, J16, J17) is used. To ensure the frequency
4.4.1 Receiver: EGSM900/GSM1800/GSM1900 –Filter to Demodulator
From the antenna switch, up to the demodulator the received signal passes the following blocks to get
the demodulated baseband signals for the EGOLD+:
Filter
LNA
Z880 Bright
Filter: The EGSM900, GSM1800 and GSM 1900 filters are located inside the frontend module. The
Filter are centred to a frequency of 942,5MHz for EGSM900, 1847,5MHz for GSM1800 and 1960MHZ
for GSM1900. The symmetrical filter output is matched via LC-Combinations to the LNA input of the
BRIGHT (D800)
LNA: The 2 LNA´s (EGSM900/GSM1800/GSM1900) are located inside the BRIGHT and are able to
perform an amplification of ~ 20dB. The LNA can be switched in HIGH (On) and LOW (Off) mode and
is controlled by the Bright depending on EGOLD+ information.
Demodulator: The Bright IC performs a direct demodulation of the received GSM signals. To do so the
LO1 is required. The channel depending LO1 frequencies for 1800MHz/1900MHz bands are divided
by 2 and by 4 for 900MHz band, Bright internally.
PGC: After demodulation the “I” and “Q” signals are amplified by the PGC-Amplifier the “I” and the “Q”
path are amplified independently from each other. The performance of this PGC is 80dB (-26 up to
54dB), switchable in steps of 2dB. The control is realised through the EGOLD+ signals (RFDATA;
RFCLK; RFSTR.
the double using of RX and TX lines), the signals are ready for further processing through the EGAIM
(part of the EGOLD+) The post-switched logic measures the level of the demodulated baseband
signal an regulates the level to a defined value by varying the PGA-Amplification and switching the
appropriate LNA gains
The required voltage VCC_SYN is provided by the ASIC D2820
(RF Control J15, J16, J17). After passing a Bright internal switch (necessary because of