26Mhz Clock (Dcxo) - LG GB108 Service Manual

26MHz Clock (DCXO)

Figure.3-3 Crystal Oscillator Functional Overview
The XO_TUNE register holds the digital correction value for the crystal oscillator frequency. The XOMODE
bits of XO_INIT1 register contain setup informations for the crystal oscillator (for example, current
programming, etc.).See Figure .3-3 Crystal Oscillator Functional Overview.
The registers XO_INIT2 and XO_INIT3 contain the coefficients information for the linearization unit of crystal
oscillator (LUXO) This linearization unit computes the required digital control word out of the programmed
AFC bits in order to have a linear pulling curve ppm vs. AFC word. The resulting digital control word DIG is
filtered by a digital lowpass filter, which can be scaled or deactivated using the bits DIGFILT0 and DIGFILT1
of the XO_INIT3 register.
The frequency correction splits into 2 parts:
1. The XOCAL bits in the XO_INIT1 register are used for the coarse frequency adjustment and are set once for
a mobile lifetime (during production test)
2. The XO_TUNE register contains the information for frequency correction when the mobile is used (correction
of temperature drift, crystal aging)
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