Pam Circuit - LG KC780 Service Manual

5.14.1 Transmitter Circuit
Transmitter Circuit
Does Power
(TP1 & TP2)
seem like
about 3dBm?
YES
Check the next part
PGND GSM850_900_IN
15
GND3 TX_EN
8
GND2
11
GND1 VRAMP
14
U501
TQM7M5005
BY_CAP2 VBATT
9
BY_CAP1
13
GSM850_900_OUT MODE_SELECT
10
DCS_PCS_OUT DCS_PCS_IN
12
Check point of PAM
- Transmitter output power (=R505, L572) is approximately 3dBm.

5.14.2 PAM Circuit

PAM circuit contains as below
- Band select switching circuitry (BS) to select GSM (Logic 0) and DCS/PCS (Logic1).
- VRAMP controls the level of output power for GMSK modulation and shape of Tx burst.
- For GMSK operation, set the PA_EN input High, and PA_MODE low(0.5v)
Operational status
Standby/PA off
Low Band GMSK Tx
Low Band EDGE Tx
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
NO
Check
U102
Fig 13 Transmitter circuit (U104)
VBAT
7
R511
6
5
4
BS
3
2
1
C520 C506 C521 C522 C507
22u
1000p 27p 100p 100p
PA_EN
0
1
1
R509
1
1
R512
1.2K
C523 C524
L503
100p 820p
NA
PA_BAND PA_MODE
X X
0 0
0 1
- 103 -
5. TROUBLE SHOOTING
TP1
TP2
TXLB
PA_EN
TX_RAMP
TP1
PA_BAND
R513 1
PA_MODE
R516 R514 1
TXHB
4.7nH
L504
DNI
TX_RAMP
X
Active
X
LGE Internal Use Only
TP2