Frequency Generation Circuitry 2-7
In achieving fast locking for the synthesizer, an internal adapt charge pump provides higher current
at pin 45 of U201 to put synthesizer within the lock range. The required frequency is then locked by
normal mode charge pump at pin 43 .
Both the normal and adapt charge pumps get their supply from the capacitive voltage multiplier
which is made up of C258, C259, C228, triple diode CR201 and level shifters U210 and U211. Two
3.3V square waves (180 deg out of phase) are first shifted to 5V, then along with regulated 5V , put
through arrays of diodes and capacitors to build up 13.3V at pin 47 of U201.
Figure 2-4 Synthesizer Block Diagram
DATA
CLK
CEX
MODIN
V
CC
, DC5V
XTAL1
XTAL2
WARP
PREIN
VCP
REFERENCE
OSCILLATOR
VOLTAGE
MULTIPLIER
VOLTAGE
CONTROLLED
OSCILLATOR
2-POLE
LOOP
FILTER
DATA (U409 PIN 100)
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