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3. TECHNICAL BRIEF
3.3 26 MHz Clock (DCXO)
Figure. 3-3 E-GoldVoice DCXO Overview
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.
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