LG -A100 Service Manual page 31

Band selection and control of transmit and receive are performed using four external control pads. Refer to the
block diagram in Figure 1 below. The band select pad, BS, selects GSM850, GSM900, DCS, and PCS modes of
operation. Transmit enable TxEN controls receive or transmit mode of the RF switch (Tx = logic 1). Proper
timing between transmit enable TxEN and Analog Power Control VRAMP allows for high isolation between the
antenna and Tx–VCO while the VCO is being tuned prior to the
transmit burst. The SKY77550 is compatible with logic levels from 1.2 V to 2.9 V for BS, TxEN, and VSW_EN pads.
ANT301
L304
1n
C343
C313
C317
2.2n
C310
SW301
C315 10p
LGE Internal Use Only
Figure 3.3.2 Band SW Logic Table
ANT304
C331
100p
100n
1p
2.2p
TX module
U301
23
24
25
L308 1n
26
C316 L309
27
18n
1p 28
29
VBAT
C347 C321
DNI
Figure 3.3.3 FEM CIRCUIT DIAGRAM
FL301
1 I1 9
O1_1
8
O1_2
7
O2_1
942.5 MHz,35 MHz
4 6
I2 O2_2
2 3 5 10
C344
4.7p
C312
DNI
RSVD2
14
GND13 RSVD1
13
GND12
GND11 BS
12
ANT VSW_EN
11
GND10 Tx_HB_IN
10
GND9
C318 33p
PGND Tx_LB_IN
9
GND
(10V,1608)
C322 C323 C329
4.7u 4.7u
3.9p
4.7p
- 31 - Copyright © 011 LG Electronics. Inc. All right reserved.
3. TECHNICAL BRIEF
RF_HB_RXP
C301 9p
L301
L313
3n
DNI
RF_HB_RXN
C304 9p
RF_LB_RXP
L315 9p
L305
L314
15n
DNI
RF_LB_RXN
L316 9p
RF_TX_EN
R304
RF_TX_RAMP
100
RF_2G_BS
C345
4.7p
RF_VLOGIC
C346
4.7p
C302 22p
R315 75
RF_HB_TX
RF_LB_TX
R316
DNI
C319
DNI
Only for training and service purposes