Samsung SCH-A302 Service Manual page 20

4. SCH-A302 Frequency Synthesizer Circuit &
Spurious radiation suppression circuit
1. Frequency Synthesizer Circuit
The Frequency synthesizer is an indirect frequency synthesizer PLL(Phased Locked Loop).
It consists of a VCTCXO(OSC401), PLL, VCO (OSC402, U402), and loop filter.
VCTCXO
The VCTCXO is a reference source of the frequency synthesizer. It provides 19.68MHz reference frequency
to PLL, VCO (OSC402, U402). The VCTCXO is a Voltage Controlled Temperature Compensated Crystal
Oscillator having 19.68 MHz ± 2.5 ppm frequency stability over all useful temperature range. A correct
frequency tuning is made by the control voltage.
VCO, PLL
The PLL, VCO Module(OSC402, U402) generates the signal having 966 ± 12.5 MHz center frequency with
the voltage control. The PLL, VCO (OSC402, U402) controls this signal.
The PLL, VCO Module(OSC402, U402) includes prescalers and charge pump. The reference divider in the
PLL, VCO Module(OSC402, U402) divides the frequency of VCTCXO by 1968 and makes reference
frequency 10kHz. This reference frequency is supplied to one of the input of phase detector. The signal
generated at the PLL, VCO Module(OSC402, U402) goes into another input stage of the phase detector
through a prescaler and the main divider.
At this point, the error proportional to the phase difference of two inputs is occurred.
This error signal is supplied to the frequency control input stage of the PLL, VCO (OSC402, U402) through
the loop filter consisted RC.
SAMSUNG Proprietary-Contents may change without notice
4-1