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CC11017 Application CircuitOnly a few external components are requiredfor using the CC1101. The recommendedapplication circuits are shown in Figure 3 andFigure 4. The external components aredescribed in Table 14, and typical values aregiven in Table 15.Bias ResistorThe bias resistor R171 is used to set anaccurate bias current.Balun and RF MatchingThe components between the RF_N/RF_Ppins and the point where the two signals arejoined together (C131, C121, L121 and L131for the 315/433 MHz reference design [5].L121, L131, C121, L122, C131, C122 andL132 for the 868/915 MHz reference design[6]) form a balun that converts the differentialRF signal on CC1101 to a single-ended RFsignal. C124 is needed for DC blocking.Together with an appropriate LC network, thebalun components also transform theimpedance to match a 50 Ω antenna (orcable). Suggested values for 315 MHz, 433MHz, and 868/915 MHz are listed in Table 15.The balun and LC filter component values andtheir placement are important to keep theperformance optimized. It is highlyrecommended to follow the CC1101EMreference design [5] and [6].CrystalThe crystal oscillator uses an external crystalwith two loading capacitors (C81 and C101).See Section 27 on page 53 for details.Additional FilteringAdditional external components (e.g. an RFSAW filter) may be used in order to improvethe performance in specific applications.Power Supply DecouplingThe power supply must be properly decoupledclose to the supply pins. Note that decouplingcapacitors are not shown in the applicationcircuit. The placement and the size of thedecoupling capacitors are very important toachieve the optimum performance. TheCC1101EM reference design ([5] and [6])should be followed closely.ComponentC51C81/C101C121/C131C122C123C124C125C126C127L121/L131L122L123L124L125L132R171XTALDescriptionDecoupling capacitor for on-chip voltage regulator to digital partCrystal loading capacitors, see Section 27 on page 53 for detailsRF balun/matching capacitorsRF LC filter/matching filter capacitor (315 and 433 MHz). RF balun/matching capacitor (868/915 MHz).RF LC filter/matching capacitorRF balun DC blocking capacitorRF LC filter DC blocking capacitor (only needed if there is a DC path in the antenna)RF LC filter/matching capacitor/DC-block (868/915 MHz)RF LC filter/matching capacitor (868/915 MHz)RF balun/matching inductors (inexpensive multi-layer type)RF LC filter/matching filter inductor (315 and 433 MHz). RF balun/matching inductor (868/915 MHz).(inexpensive multi-layer type)RF LC filter/matching filter inductor (inexpensive multi-layer type)RF LC filter/matching filter inductor (inexpensive multi-layer type)RF LC filter/matching filter inductor (inexpensive multi-layer type) (868/915 MHz)RF balun/matching inductor. (inexpensive multi-layer type)Resistor for internal bias current reference.26MHz - 27MHz crystal, see Section 27 on page 53 for details.SWRS061C Page 18 of 94