26 Mhz Clock (Dcxo) - LG 410G Service Manual

3.3 26 MHz Clock (DCXO)

NC10
NC11
NC12
NC13
NC14
NC15
NC16
NC17
NC18
NC19
SPARE3
SPARE2
XTAL
DCXO (Digitally Controlled Crystal Oscillator) and VCTCXO (Voltage Controlled Temperature
Compensated Crystal Oscillator) are two different techniques used to maintain the mobile's reference
oscillator's accuracy over time. The reference oscillator's accuracy over time will vary due to initial
crystal frequency offset, temperature drift and aging. These static and dynamic frequency variations have
to be compensated, otherwise the mobile would be in danger of losing connection to the network.
The technique used to perform the frequency compensation is generally termed Automatic Frequency
Control (AFC). To summarize the operation of DCXO, GSM Baseband processor will calculate the
AFC compensation (which is continuously updated) required based on the measured frequency error.
Then the required AFC compensation is sent to the LUXO (Lineari-Zation Unit of Crystal Oscillator),
which in turns control the DCXO core and generates the 26MHz system clock.
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
C107
1000p
R104
J12
220K
H12
G12 R105
L11
1.5M
K11
J11
H11
L10
K10
J10
U1
U2
D15
Figure. 3-3 Locosto DCXO Overview
-17-
X101
W-191-866
4
3
GND2 HOT2
1 GND1 2
HOT1
26MHz
C108 C109
0.5p 10p
C112
4.7p
- 21 -
3. H/W Circuit Description
DITHERING
LGE Internal Use Only