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MRF89XA Folha de dados(PDF) 64 Page - Microchip Technology |
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MRF89XA Folha de dados(HTML) 64 Page - Microchip Technology |
64 / 140 page MRF89XA DS70000622D-page 64 Preliminary 2010-2017 Microchip Technology Inc. 3.4.6 CHANNEL FILTERS SETTING IN OOK MODE The center frequency, fo, is set to 100 kHz by default. The chart in Figure 3-8 illustrates the receiver bandwidth when the BUTFILV<3:0> bits (FILCREG<3:0>) are changed when the polyphase filter is activated. Table A-2 suggests a few filter settings in OOK mode along with the corresponding passive filter bandwidth, and Table 4-2 specifies the accepted tolerance on the crystal reference. 3.4.7 RECEIVED SIGNAL STRENGTH (RSSI) After filtering, the In-phase and Quadrature signals are amplified by a chain of 11 amplifiers, each with 6 dB gain. The outputs of these amplifiers are used to evaluate the RSSI. 3.4.7.1 Resolution and Accuracy When the RSSI resolution is 0.5 dB, the absolute accuracy is not expected to be better than ±3 dB due to process and external component variation. Higher accuracy while performing absolute RSSI measurements requires additional calibration. FIGURE 3-8: ACTUAL BW OF POLYPHASE FILTER 3.4.7.2 Acquisition Time In OOK mode, the RSSI evaluates the signal strength by sampling I(t) and Q(t) signals 16 times in each period of the chosen IF2 frequency (refer to Section 2.10.1, Receiver Architecture). In FSK mode, the signals are sampled 16 times in each fdev period, fdev being the frequency deviation of the companion transmitter. An average is then performed over a sliding window of 16 samples. Therefore, the RSSI output register RSTSREG (RSSIVAL<7:0>) is updated 16 times in each fdev or IF2 period. The following settings are recommended: • FSK Mode: Ensure that the fdev parameter (as described in the FDEVREG register (Register 2-3) through the FDVAL<7:0> bits)) remains consistent with the actual frequency deviation of the companion transmitter. • OOK reception: Ensure that the fdev parameter (as described in the FDEVREG register (Register 2-3) through the FDVAL<7:0> bits)) is equal to the frequency of the I(t) and Q(t) signals (that is, the second Intermediate Frequency, IF2, of the receiver). Note that, this IF2 equals fo, the center frequency of the polyphase filter. Polyphase Filter's BW, OOK 0 50 100 150 200 250 300 350 400 450 04 8 10 12 14 Val (BUTFILV<3:0>) [d] POLCFV<3:0> = 0011 16 Actual BW Theoretical BW 26 |
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