| Input/Output MatchingWhen using an unbalanced antenna such as a monopole, a balun should be used to optimize performance. Thebalun can be implemented using low-cost discrete inductors and capacitors. The recommended balun shownconsists of C262, L261, C252, and L252.If a balanced antenna such as a folded dipole is used, the balun can be omitted.CrystalAn external 32-MHz crystal, XTAL1, with two loading capacitors (C221 and C231) is used for the 32-MHz crystaloscillator. See the 32-MHz Crystal Oscillator section for details. The load capacitance seen by the 32-MHzcrystal is given by:(1)XTAL2 is an optional 32.768-kHz crystal, with two loading capacitors (C321 and C331) used for the 32.768-kHzcrystal oscillator. The 32.768-kHz crystal oscillator is used in applications where both very low sleep-currentconsumption and accurate wake-up times are needed. The load capacitance seen by the 32.768-kHz crystal isgiven by:(2)A series resistor may be used to comply with the ESR requirement.On-Chip 1.8-V Voltage-Regulator DecouplingThe 1.8-V on-chip voltage regulator supplies the 1.8-V digital logic. This regulator requires a decoupling capacitor(C401) for stable operation |
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