Crystal(26 Mhz, X100) - LG -T300 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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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
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3. TECHNICAL BRIEF
3. TECHNICAL BRIEF
LGE Internal Use Only