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IC201 LMX2331L RF-PLL
8
13MHz
DIV
200Khz
CLK
65
PHASE
DIFFERENCE
(CURRENT)
The TX UHF Synthesiser
The TX UHF Synthesiser (RF-PLL) is the same as the PLL used in the RX and is
contained in the LMX2331L (IC201).
In TX mode the TX UHF VCO output is fed to #5 (IC201) and then pre-scaled down
to 200khz.
The phase comparator within IC201 compares this signal with a 200khz signal
derived from the 13Mhz clock and outputs a current phase difference at #3.
A loop filter then converts this signal into a voltage phase difference and feeds it
to #3 (IC201) or (IC202).
The voltage phase difference determines the UHF VCO frequency i.e. GSM TX
1160Mhz -1185Mhz, PCN TX 1530Mhz - 1610Mhz .
Three control inputs are used in the UHF Synthesiser SERDA, SERCK, SERLT. It is
the SERDA control input which initially sets the TX VCO frequency. This is totally
dependent on the chosen traffic channel the logic circuit has selected at the time.
Fig.7: The UHF Synthesiser (TX)
PHASE
COMPARATOR
PRE-
200Khz
SCALER
3
PHASE
DIFFERENCE
(VOLTAGE)
LOOP
FILTER
GND
11,12,13
5
EG:1160Mhz (GSM)
V_VC01/2
NC
1
4
3
2
OUT
IN
UHF VCO
5
(IC201/2)
GND
SERLT
SERDA
SERCK
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