Dual Mode Operation - LG KE820 Service Manual

3. TECHNICAL BRIEF
PIN Function
1 HB_RFIN
2 BAND_SEL
3 TX_EN
4 VBATT
5 VMODE
6 VRAMP
7 LB_RFIN
8,9,10,11 GND
12 LB_RFOUT
13,14,15,16,17 GND
18 HB_RFOUT
19,20,21,22,23 GND

3.26.1 Dual Mode Operation

When VMODE is low, the voltage on VRAMP is used to regulate the PA collector voltage which
directly controls the output power. When VMODE is high, the PA collector voltage is regulated to
3.6V, and the supply for the PA base bias can be adjusted via the VRAMP pin to optimize current
drain for low or high power ranges. In addition, in 8PSK mode, the first stage of the low band PA is
bypassed to decrease gain, but in high band, the PA operates with all stages.
MODE VMODE
GSM Low
EDGE High
NA NA
C410 C411
L407
3.9nH
R408
0
L406
C412
10nH
NA
Description
RF input to the High-band PA
Logic low=low band, Logic high=high band select
PA Enable
Main supply
Logic low=GMSK mode, Logic high=8PSK mode select
Ramped burst pin
RF input to the Low-band PA
Ground
RF output from the low-band PA
RF output from the high-band PA
Table 13 PAM pin description
RF INPUT
Fixed
Ramp Burst Control
NC3 LB_RFIN
20
NC2 U401 VRAMP
15
NC1 VMODE
RF3158
10
VBATT
LB_RFOUT TX_EN
12
BAND_SEL
HB_RFOUT HB_RFIN
18
Figure 42 PAM schematic
- 68 -
VRAMP
Ramp Burst Control
Control amp bias current
VSUPPLY
7
6
5
4
3
2
1
C401 C402 C409
100p 100p 100p
C408 C414
68u
27p
TX ENABLE
High
High
LBAND_PAM_IN
R407
PA_LEVEL
0
MODE
TXON_PA
PA_BAND
HBAND_PAM_IN
C403
100p