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Fig.3:The IF AMP and Demodulator
PMB2410 (IC300)
First Mixer
1st IF
270Mhz
8-9
20-21
FL304
From (IC201#18) IF PLL (See Fig.4)
Rx I&Q Demodulator
The modulated IF signal of 270Mhz is demodulated by mixing it with another
270Mhz signal, which is derived from an 540Mhz oscillator located inside IC300.
The 540Mhz is reduced by a pre-selectable divider, which can be set by the
control signal GSM_TX (from IC27#23). The output from the 540Mhz oscillator is
divided down by a factor of 2 or 3 to produce either a 180 or 270Mhz signal,
depending on whether the mobile is in TX or RX modes . It is this signal which is
mixed with that from the IF amplifier to produce the baseband I and Q signals. The
I and Q signals are then buffered and fed differentially to the Superchip (IC27) for
filtering and digitising.
The signal RX_ON2 (from IC27#28) enables both the demodulator and internal
buffers. The signal PUPLO2 which is supplied from IC27 #26, enables the
540Mhz internal oscillator.
11,12,13
270Mhz
RINO
Div2
540MHz
Div2/3
32-35
Varactor Network
D303 (A,B)
LOOP FILTER
AGC Control
46
RINO
45
RIPO
40
RQNO
39
RQPO
36
31
23-24
GSM_TX
TO W2013 (IC100)
(TX IF Modulator)
:-PGSTR
SYGCCL
SYGCDT
RX_ON2
PUPLO2
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