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CC1070-RTR1 数据表(PDF) 39 Page - Texas Instruments |
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CC1070-RTR1 数据表(HTML) 39 Page - Texas Instruments |
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39 / 57 page  CC1070 SWRS043A Page 39 of 54 switching the PA back on after a hop has been performed. Note that the override bits VCO_OVERRIDE, CHP_OVERRIDE and VCO_CAL_OVERRIDE must be disabled when performing a re-calibration. 22 PCB Layout Recommendations A two layer PCB with all components placed on the top layer can be used. The bottom layer of the PCB should be the “ground-layer”. The top layer should be used for signal routing, and the open areas should be filled with metallization connected to ground using several vias. The area under the chip is used for grounding and must be connected to the bottom ground plane with several vias. In the TI reference designs we have placed 8 14 mil (0.36 mm) diameter via holes symmetrically inside the exposed die attached pad. These vias should be “tented” (covered with solder mask) on the component side of the PCB to avoid migration of solder through the vias during the solder reflow process. Each decoupling capacitor should be placed as close as possible to the supply pin it is supposed to decouple. Each decoupling capacitor should be connected to the power line (or power plane) by separate vias. The best routing is from the power line (or power plane) to the decoupling capacitor and then to the CC1070 supply pin.. Supply power filtering is very important, especially for the VCO supply (pin 15). Each decoupling capacitor ground pad should be connected to the ground plane using a separate via. Direct connections between neighboring power pins will increase noise coupling and should be avoided unless absolutely necessary. The external components should ideally be as small as possible and surface mount devices are highly recommended. Precaution should be used when placing the microcontroller in order to avoid noise interfering with the RF circuitry. A CC1020/1070DK Development Kit with a fully assembled CC1070EM Evaluation Module is available. It is strongly advised that this reference layout is followed very closely in order to obtain the best performance. The layout Gerber files are available from the TI web site. 23 Antenna Considerations CC1070 can be used together with various types of antennas. The most common antennas for short-range communication are monopole, helical and loop antennas. Monopole antennas are resonant antennas with a length corresponding to one quarter of the electrical wavelength ( λ/4). They are very easy to design and can be implemented simply as a “piece of wire” or even integrated onto the PCB. Non-resonant monopole antennas shorter than λ/4 can also be used, but at the expense of range. In size and cost critical applications such an antenna may very well be integrated onto the PCB. Helical antennas can be thought of as a combination of a monopole and a loop antenna. They are a good compromise in size critical applications. But helical antennas tend to be more difficult to optimize than the simple monopole. Loop antennas are easy to integrate into the PCB, but are less effective due to difficult impedance matching because of their very low radiation resistance. |
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