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ben-wpan/atrf/ecn/ecn0002.txt
Werner Almesberger 2406f674f5 More RF research for the ECNs (balun and layout)
- atrf/ecn/ecn0001.txt, atrf/ecn/ecn0002.txt: changed ECN format to
  separate title from body by two blank lines and, where a conclusions has
  been reached, put it into a section separated from body also by two blank
  lines
- atrf/ecn/ecn0003.txt: researched balun design and availability
- atrf/ecn/INDEX, atrf/ecn/ecn0004.txt: new ECN: Take into account layout
  considerations for RF
- TODO: removed item covered by ECN0002
- TODO: removed bug fixed in f32xbase commit
  79396b17772639cea615d1c87870d55f08c11850
- TODO: added reference to ECN0003
2010-08-26 15:41:14 -03:00

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