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49 lines
1.4 KiB
Plaintext
49 lines
1.4 KiB
Plaintext
Add load capacitors to 16 MHz crystal (C14, C15)
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The crystal has a specified load capacitance of 8 pF. The AT86RF230 has
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an internal capacitor array that can be trimmed in 16 steps from 0 pF to
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4.5 pF.
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The crystal has a nominal tolerance of 15 ppm at 25 C plus a temperature
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tolerance of 15 ppm. The following deviations from 1 MHz at CLKM were
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measured with the CNTR board, roughly at 20-25 C:
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Board Error Meas. accuracy C14/C15 Trim
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(f, ppm) (ppm, nom.) (pF) (pF)
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--------------- --------------- --------------- ------------ --------
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2, "orange" +268 99.6 NC 0
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+266 99.5 NC 0
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+266 40.0 NC 0
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+148 99.8 NC 3.0
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+147 99.7 NC 3.0
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+147 40.0 NC 3.0
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+111 100.0 NC 4.5
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+110 99.8 NC 4.5
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- 13 99.9 15 0
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- 14 100.0 15 0
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+ 11 99.9 12 0
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+ 11 99.6 12 0
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(cleanup) + 14 100.0 12 0
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+ 14 100.0 12 0
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1, "red" +263 99.7 NC 0
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+263 100.0 NC 0
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+107 99.3 NC 4.5
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+108 100.0 NC 4.5
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+ 24 99.8 10 0
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+ 24 100.0 10 0
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- 9 99.7 10 4.5
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- 9 100.0 10 4.5
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(cleanup) + 14 100.0 12 0
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+ 14 100.0 12 0
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(Multiple measurements to assess CNTR performance and drift. Note that
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CNTR measurements are repeatable within 1 ppm, so the nominal accuracy
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appears to be far too pessimistic.)
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Conclusion: these measurements suggest that, combined with parasitic
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capacitance, load capacitors of 12 pF make the crystal roughly half the
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trim range faster than 16 MHz.
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