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4. RF Circuit Technical Brief
4.3.3 Synthesizer
The receiver and the transmitter contain each a complete fractional-N RF synthesizer with fast locking. The
VCO’s run at 4 GHz and the RX and TX frequencies are obtained through division by two (bands I, II, III and IV)
or four (bands V and VI). The PLL loop filters are fully integrated. The reference frequency has to be provided
by an external clock.
The total VCO frequency range is divided in 256 subranges, in order to limit the VCO slope. Before the settling
process of the PLL starts, a successive approximation algorithm selects the most appropriate subrange.
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