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3. TECHNICAL BRIEF
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.
LGE Internal Use Only
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
Only for training and service purposes
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