LG KG271, Service Manual

Page: 31 / 126

The digital transmitter architecture is based on a fractional-N sigma-delta synthesizer for constant
envelope GMSK modulation. This configuration allows a very low power design with a reduced
external component count.
The modulation is transferred between baseband- and RF-part of the PMB7880 via a digital interface
signal into the digital modulator.
The following Gaussian filter shapes the digital data stream for the GMSK modulation. Additionally a
pre-distortion filter compensates the attenuation of the PLL transfer function resulting in a very low
distortion at the transmit output.
The filtered digital data stream is scaled appropriately and added to the channel word. This sum is fed
into the MASH modulator. The output of the MASH modulator is a sequence of integer divider values
representing the high resolution fractional input signal. This sequence controls the MMD (multi
modulus divider) at a sample rate of 26MHz. Thus a tightly controlled frequency modulation of the
VCO is achieved.
3. TECHNICAL BRIEF
- 32 -
Figure 3-9-3. PAM(Power Amplifier Module) interface
(50V,J,NP0)
(50V,J,NP0)
(2012)
(16V,K,X7R)
(10V,Z,Y5V) (50V,J,NP0)
(16V,K,X7R)
(50V,J,NP0)
VBAT
C414
27p
VBAT
L402
NA
27p
C407 C408
0.01u
GND7
13 14
GND8
16
GND9
P_GND
21
RSVD_GND
19
20
VAPC
VBATT
17
VCC1A
2
VCC1B
6
1
BS
3
DCS_PCS_IN DCS_PCS_OUT
15
EGSM_IN
4
EGSM_OUT
11
18
ENABLE
5
GND1 GND2
7
GND3
8 9
GND4 GND5
10 12
GND6
NA
U400
SKY77318
C416
C405
R407
0
33p
C412
NA
39p
C415
NA
C401
0
R404
C411
NA
C402
10u
R410
0
R408
NA
C409
NA
C404
0.01u
R402
1K
0
R406
R405
0
27p
C413
R409
NA
12p
C403
18p
C406
DCS_PCS_OUT
TXON_PA
BS
GSM_OUT
TX_RAMP