LG LG-A130, Руководство по обслуживанию

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3. TECHNICAL BRIEF
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3.4 Crystal(26 MHz, X101)
Figure. 3.4.2 Digital PREDISTORTION with LUXO
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.
Figure. 3.4.1 Crystal Oscillator External Connection
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
3. TECHNICAL BRIEF
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