The radio part of the C45, M50 AND MT50 consists of a Hitachi RF chip-set.
The radio part is designed for Dual Band operation, covering EGSM900 as well
as GSM 1800 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 directly connected to the battery. The voltages for the logic part are
generated by the Power-Supply ASIC
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 (www.etsi.org) After amplification 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 can then be 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.
M46 mobile is using a reference frequency of 26MHz for the Hitachi chip set.
The generation of the 26MHz signal is done via a discrete “Colpitts” VCXO .
This oscillator consists mainly of:
A 26MHz crystal Z950
An oscillator switch V950
A capacity diode V951
TP 951 after dividing by two
The oscillator output signal is directly connected to the BRIGHT IC (pin 38) to be
used as reference frequency inside the Bright and to be divided by 2.
This so gained signal SIN13MHZ_BB is used from the EGOLD+(functional M14).
To compensate frequency drifts (e.g. caused by temperature) the oscillator
frequency is controlled by the (AFC_PNM) signal, generated through the internal
EGOLD+ (D100 (functional R3)) PLL via the capacity diode V951.
Reference 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+(baseband L4) via R136 as
the signal TENV.
The required voltage VCC_OSC is provided by the N840 (VCC_SYN)through
R863 and R861
Waveform of the AFC_PNM signal from EGOLD+ to Oscillator
The first local oscillator is needed to generate frequencies which enable the
transceiver IC to mix an “IF” 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 -IC).
This control voltage is a result of the comparison of the divided LO1 and a reference
Signal. The division ratio of the dividers is programmed by the EGOLD+, according
to the network channel requirements.
The first local oscillator (LO1) is part of the PLL which consists of the comparator
inside the Bright(D800), a loop filter and the VCO (Z850) module.
This LO1 circuit generates frequencies from:
3610-3760 MHz for GSM900
3700-3840 MHz for GSM1800
(The VCO can be switched via the signal VSW (Pin 3) to generate frequencies for
GSM900 and GSM1800)
RX IF = no IF required TX IF-GSM900 = 45…46MHz
TX IF-GSM1800 = 90…92MHz
Formula to calculate the frequencies:
1st LO freq. RX EGSM = Ch. * 4
PCN = Ch. * 2
The VCO (Z850) is switched on by the EGOLD+ signal PLLON (TDMA-Timer J12)
via V850 and therefore supplied with VCC_SYN. The VCO guarantees by using the
control voltage at pin5 a coverage of the GSM900 and GSM1800 band.
The channel programming of the PLL happens via the EGOLD+ signals SYGCCL,
SYGCDT, SYNSTR(RF Control K14, K15, M15).
The required voltage VCC_SYN is provided by the N840
The second local oscillator (LO2) consists of a PLL and a VCO which are
integrated in Bright IV and a second order loopfilter which is realized external.
Due to the direct conversion receiver architecture, the LO2 is only used for
transmit-operation. To avoid inband-spurious in the transmit-signal, the
LO2-frequency assignment is not fixed for the whole band.
Before the LO2-signal gets to the modulator it is divided by 8 for GSM900 and by 4
for GSM1800. So the resulting
TX-IF frequencies are 45…46 MHz. GSM900
TX-IF frequencies are 90…92 MHz. GSM1800
nd
2
LO freq. = 360…368 MHz divided by 8 = 45…46 MHz,
divided by 4 = 90…92 MHz
The LO2 PLL and power-up of the VCO is controlled via the tree-wire-bus of
Bright IV+.(EGOLD+ signals SYGCCL, SYGCDT, SYNSTR(RF Control K14, K15, M15))
The required voltage VCC_SYN is provided by the N840