LG KG270 Service Manual page 31

3. TECHNICAL BRIEF
C402
C403 C404 C405 C406
10u
12p 0.01u 33p 18p
(2012)
R406
0
C411 C412
NA NA
R410
0
C416
C415
NA NA
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.
VBAT
15
DCS_PCS_OUT DCS_PCS_IN
11
U400
EGSM_OUT EGSM_IN
SKY77318
19
RSVD_GND ENABLE
21
P_GND
Figure 3-9-3. PAM(Power Amplifier Module) interface
VBAT
C407 C408
27p 0.01u
(50V,J,NP0) (16V,K,X7R)
3
4
18
1
BS
C413 C414
27p 27p
- 32 -
R404 R405
0 0
L402
NA
C409
NA
R407
0
TXON_PA R409
R408
NA NA
BS
DCS_PCS_OUT
GSM_OUT