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Crystal Oscillator
Crystal oscillator (X100) employs a 19.2 MHz Temperature Compensated Crystal Oscillator (TCXO),
and its reference frequency is calibrated by the digital-to-analog converter IC (U500) for accuracy.
PLL IC
The PLL IC (U100) is a fractional frequency divider IC. The logic switch ICs (U101 and U102) work with
the PLL IC (U100) to achieve locking.
Registers
MSB/LSB
Dividend
Divider
PD/Charge Pump
& Pwr-Dn/Mux Out
Control
Reference
Frequency Dividers
Serial
Interface
Modulation
Unit
Fractional
Unit
ΔΣ
18-Bit
Main
Divider
Main
Divider
Main Phase/
Freq.Detector
and
Charge Pump
Reference
Frequency
Oscillator
Reference
Frequency
Oscillator
M
u
x
Mux_out
Ref
Data
Clock
CS
Mod_in
Fvco_main
Fvco_main
CPout_main
LD/PS_main
Lock Detection or
Power Steering
Fref_main
Fref_main
The 19.2 MHz frequency generated by the crystal oscillator (X100) goes into the PLL IC (U100) for
frequency division, generating the reference frequency. Meanwhile, the frequency generated by VCO
goes into PLL IC (U100) for frequency division. The resulting frequency will be compared with reference
frequency in terms of phase difference in the phase detector. After comparison, the resulting frequency
is converted to CV voltage via the loop filter, to control and lock the frequency.
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