LGE Internal Use Only
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3.3 26 MHz Clock (DCXO)
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.
3. HW Circuit Description
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Figure. 3-3 Locosto DCXO Overview
GND1 2
4
GND2
HOT1
1
3
HOT2
26MHz
W-191-866
X101
C112
4.7p
R104
220K
C109
10p
C108
0.5p
1000p
C107
XTAL
D15
L8
U2
SPARE2
U1
SPARE3
J12
NC10
NC11
H12
NC12
G12
NC13
L11
K11
NC14
NC15
J11
H11
NC16
L10
NC17
NC18
K10
J10
NC19
R105
1.5M
DITHERING