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13MHz
8
DIV
CLK
13
PHASE
DIFFERENCE
(CURRENT)
The TX IF Synthesiser
TX IF Synthesiser(IF-PLL) is the same PLL as used in the RX process and is
located within the LMX2331L (IC201). In this case the synthesiser is used to tune
the 540Mhz TX IF oscillator inside IC300.
The 540Mhz signal from IC300 is divided by a factor of 2 (for GSM) to produce a
270Mhz signal or divided by 3 (for PCN) to produce a 180Mhz signal.
This signal is then fed to #16 (IC201) and #9 (IC100) the TX modulator.
At IC201, it is divided down further by a factor of 180 or 270, dependant on which
tx band the mobile is set to. This produces a 1Mhz signal which is then input to a
phase comparator where it is compared with a 1Mhz signal derived from the
13Mhz clock to produce a current phase difference signal. This signal is output
from IC201 on #18 to the loop filter (C218, C219, R202, C228, R283, R204 &
L205), which aswell as filtering the signal also converts it to a phase difference
voltage. The phase difference voltage is then applied to the varactor network
(D303 A/B).
The varactor network forms part of the 540Mhz oscillator circuit inside IC300 and
is tuned by the applied voltage.
Fig.5: The IF Synthesiser (TX)
IC201 LMX2331L IF-PLL
PHASE
COMPARATOR
DIV 180
1Mhz
1Mhz
or 270
18
PHASE
DIFFERENCE
(VOLTAGE)
LOOP
FILTER
180 or 270Mhz
GSM_TX
D303B
D303A
GND
IC300
180 or 270Mhz
16
23-24
32
33
34
35
PUPLO2
31
540Mhz
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