Lo Generation And Distribution Circuits; Off-Chip Rf Components; Only For Training And Service Purposes - LG U990 Service Manual

3.4 LO generation and distribution circuits

The integrated LO generation and distribution circuits are driven by internal VCOs to support various
modes to yield highly flexible quadrature LO outputs that drive all GSM/EDGE and UMTS band
upconverters and downconverters; with the help of these LO generation and distribution circuits, true
zero-IF architecture is employed in all GSM and UMTS band receivers and transmitters to translate the
signal directly from RF to baseband and from baseband to RF.
Two fully functional fractional-N synthesizers, including VCOs and loop filters, are integrated within the
RTR6275 IC. The first synthesizer (PLL1) creates the transceiver LOs that support the UMTS
2100/1900/1800 transmitter, and all four GSM band receivers and transmitters including: GSM850,
GSM900, DCS1800, and PCS1900. The second synthesizer (PLL2) provides the LO for the UMTS
2100/1900/1800 receiver. An external TCXO input signal is required to provide the synthesizer
frequency reference to which the PLL is phase and frequency locked. The RTR6275 IC integrates
most of PLL loop filter components onchip except two off-chip loop filter series capacitors, and
significantly reduces off-chip component requirement. With the integrated fractional-N PLL
synthesizers, the RTR6275 has the advantages of more flexible loop bandwidth control, fast lock time,
and low-integrated phase error.

3.5 Off-chip RF Components

3.5.1 UMTS PAM (U105: AWT6277R)
The UMTS PA output power is monitored by power detector circuits (U101 : RTR6275) . This detector
voltage can be used for transmitter calibration and monitor to meet RF system specification.
FL103
SAYZY1G95EB0B00
C169 5.6p
Copyright © 2007 LG Electronics. Inc. All right reserved.

Only for training and service purposes

+VPWR
C160 C162 C163
22u
0.01u 100p
U104
C170
SCDY0003403
1.8p
4.7nH
L128 L126
8.2nH
20dB
R124
R123
51
PWR_DET
68
R125 R126
100
100
8 dB
[Figure 1.5] UMTS PAM, Duplexer, Coupler
C159
8.2p
C164
1u
L123
L124
15nH
3.3nH
U105
11
GND5
10 1
VCC2 VCC1
9 2
GND4 RFIN
8 3
RFOUT GND1
7 4
GND3 VMODE
6 5
Q100
GND2 VREF
AWT6277R
C173
100p
KRX102E
- 27 -
3. TECHNICAL BRIEF
FL104
EFCH1950TDF1
4 5 C161
O1 G3
1
IN WCDMA_2100_TX_OUT
G2 G1
56p
3 2
C165
L122
NA
NA
PA_R1
VREG_TCXO_2.85V
PA_ON
LGE Internal Use Only