LG KT520 Service Manual page 75

3. TECHNICAL BRIEF
C. Synthesizer
The RX and TX RF VCOs are fully integrated and self-calibrated on manufacturing tolerances.
They have 16 different frequency ranges that are selected internally depending on the frequency
programming. The calibration is done on each low to high logical transition of the SYNON bit in the
control register or on each change of the integer divider ratio of the RF fractional N synthesizer.
A high-performance RF fractional-N synthesizer PLL is included on-chip which enables the frequency
of the RF VCO to be synthesized. The frequency is set through the 3-wire serial programming bus.
The PLL is based on Sigma-Delta (∑) fractional-N synthesis that enables the required channel
frequency, including Automatic Frequency Control (AFC) from a free running external 26 MHz
reference frequency. Very low close-in-phase noise is achieved. This allows widening of the PLL loop
bandwidth and shorter settling time. The programmable main dividers are controlled by a second order
∑ -modulus controller. They divide the RF VCO signals down to frequencies of 26 MHz (12 Hz step
programmability). Their phase is then compared in a digital Phase/Frequency Detector (PFD) to the 26
MHz reference clock signal.
The phase error information is fed back to the RF VCO through the charge pump circuit that .sources.
into or .sinks. current from the loop filter capacitor, thus changing the VCO frequency such that the
loop finally gets phase-locked.
5 2
C219
G2 G1
WTXMOD_BAND_I
OUT IN
4 1
G3
SAFEB1G95KA0F00 3 FL202
VRADA_2V8
WTX_I_P
WTX_I_N
WTX_Q_P
WTX_Q_N
LGE Internal Use Only
C218
DNI
FL201
VRADA_2V8
56p
WPA_BIAS
WPA_VCC
1
GNDTX
2
NC1
3
NC2
4
U204
TX_1
5
NC3
6
VCCLOTX
7
TXIA
8
RF3100_OM6195HN
TXIB
9
TXQA
10
TXQB
RF_CTRL_DATA
RF_CTRL_CLK
RF_CTRL_STRB
C230 5.6p
WCLK
Figure 3-7-4. WCDMA Transceiver schematic
- 76 -
C217
56p
SAFEB2G14FA0F00
VRADA_2V8
VDIGRAD_1V8 VRADA_2V8
30
NC9
29
LNA1_OUT
28
NC8
27
LNA1_IN
26
NC7
25
NC6
24
VCCLORX
23
NC5
22
VDD
21
TST
R206 200
WRX_Q_N
R207 200
WRX_Q_P
R208 200
WRX_I_N
R209 200
WRX_I_P
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
C225 5.6p
WRX_BAND_1
L205
4.7nH