Crystal(26 Mhz, X100) - LG GB230 Service Manual

3.4 Crystal(26 MHz, X100)

Figure. 3.4.1 Crystal Oscillator External Connection
The DCXO tuning characteristic should be a first order linear function of the programming word AFC. The
variable capacitance array is a first order linear function of the digital word DIG, which leads to a nonlinear
curve ppm vs. DIG (and also a nonlinear ppm vs. AFC for DIG=AFC). In order to linearize the ppm vs. AFC
curve the implementation of a predistortion is necessary.
To get the wanted linear ppm vs. AFC tuning curve some digital predistortion of the AFC word is required.
This predistortion is performed by the linearization unit for crystal oscillator (LUXO). The LUXO calculates
the corresponding DIG value according to the given AFC value.
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Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
Figure. 3.4.2 Digital PREDISTORTION with LUXO
The X-GOLDTM213 RF-Subsystem contains a
fully integrated 26 MHz digitally controlled
crystal oscillator, designed for 8 pF crystals.
The only external part of the oscillator is the
crystal itself. Overall pulling range of the DCXO
is approximately ±55 ppm, controllable by a
13-bit tuning word.
This frequency serves as comparison
frequency within the RF-PLL and as clock
frequency for the digital circuitry.
The 26 MHz reference clock can also be
applied to external components like Bluetooth
or GPS, via the two buffered output signals
FSYS1 and FSYS2
Copyright © 2007 LG Electronics. Inc. All right reserved.
Only for training and service purposes
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3. TECHNICAL BRIEF
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