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MRF89XA Scheda tecnica(PDF) 94 Page - Microchip Technology |
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MRF89XA Scheda tecnica(HTML) 94 Page - Microchip Technology |
94 / 140 page MRF89XA DS70000622D-page 94 Preliminary 2010-2017 Microchip Technology Inc. 4.2 RF Transmitter Matching The optimum load for the RF port at a given frequency band is listed in Table 4-1. These load values in the table are expected by the RF port pins to have as an antenna load for maximum power transfer. For all antenna applications, an RF choke inductor (L2) must be included during transmission because the RF out- puts are of open-collector type. 4.3 Antenna Components The MRF89XA is single-ended and has an unbalanced input and output impedance close to 30-j25. Therefore, it only requires a matching circuit to the SAW filter and antenna. The C11, C12, and L6 are part of the match- ing network these components make for the antenna circuit. L1, C4, and C5 are tuned to provide that impedance (30+j25) to the RFIO pin. In this case, the transceiver can transfer all power toward the antenna. This impedance is called Optimum Load Impedance. L2 is an RF choke inductor. L3 and L4 are VCO induc- tors. The details are shown in Figure 4-1. TABLE 4-1: ANTENNA LOAD VALUES FOR 868 MHz AND 915 MHz FREQUENCY BANDS 4.4 SAW FILTER FL1 is a SAW filter. While in Transmitting mode, the SAW filter is used to suppress the harmonics. While in Receiving mode, the SAW filter is used to reject the image frequencies and out-of-band interfering signals. 4.4.1 SAW FILTER PLOT Figure 4-2 and Figure 4-3 illustrate the plots of the SAW filter used in the application circuit. The plots shown are representative. For exact specifications, refer to the SAW Filter manufacturer data sheet. Band FL1 C5 C4 L1 868 MHz TA0801A 1.8 pF 22 pF 8.2 nH 915 MHz TA0281A 1.8 pF 30 pF 10 nH Note 1: The SAW filter can be of EPCOS (B3717 and B3588) or Taisaw (TA0801A and TA0281A) for 868 MHz and 915 MHz respectively with matching components remaining the same as shown in Figure 4-1 and Table 4-1. |
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