J.phase Frequency Detector/Charge Pump; K.synthesizer Loop Filter; L.voltage Controlled Oscillator; The Crystal Reference System - LG KG110 Service Manual

prescaler, integer M & A dividers, and fractional N system based on sigma-delta modulation
to generate the required fractional divide ratio. The Denominator of the fractional divider can
be set to 3 different values, (1040, 1170, 1235), depending on the mode of operation.
For example a denominator of 1040 with an input fraction F maintains an average value of
F/1040 allowing 25 kHz steps when operated at a reference of 26 MHz.
J. Phase Frequency Detector/Charge Pump
A Phase Frequency Detector (PFD) is used for the PLL phase detector.
The charge pump is designed such that good matching of up and down currents is
achieved over a wide output operating range. The charge pump output is internally routed to
the integrated synthesizer loop filter.
K. Synthesizer Loop filter
To minimize complexity of the external PCB layout the Main Synthesizer loop filter
is also fully integrated into the IC. No external components or adjustments are required .

L.Voltage Controlled Oscillator

The integrated voltage controlled oscillator (VCO) is a complete self-calibrating
subsystem. This employs a fully automated digital self-calibration function to
ensure optimum phase noise performance over the entire frequency range.
The VCO generates frequencies between 2520MHz and 2985MHz as required to operate in
the four bands for RX and TX.

3.2.3 The Crystal Reference System

The AD6548 requires only an external low cost crystal as the frequency reference.
The circuitry to oscillate the crystal and tune its frequency is fully integrated.
The Oscillator is a balanced implementation requiring the crystal to be connected
across 2 pins. There is a programmable capacitor array included for coarse tuning
of fixed offsets (e.g. crystal manufacturing tolerance), and an integrated varactor for
dynamic control. The oscillator is designed for use with a 26MHz crystal.
The crystal is connected as shown in figure.
Dedicated control software ensures excellent frequency stability under all
circumstances.
VCTCXO
Supply
Ref
Figure 3-4: The Crystal Reference System
13
3. TECHNICAL BRIEF
VAFC
AFC
REFINB
REFIN
REF_OP
CLK
REF_OP
VCC_REF