Root/atrf/ecn/ecn0002.txt

Source at commit fe8bdac37f8061fa43f8df92ab51ae31aa113bcf created 13 years 7 months ago.
By Werner Almesberger, atrf/ecn/ecn0002.txt: added measurements after making boards use 12 pF and cleaning up the soldering.
1Add load capacitors to 16 MHz crystal (C14, C15)
2
3The crystal has a specified load capacitance of 8 pF. The AT86RF230 has
4an internal capacitor array that can be trimmed in 16 steps from 0 pF to
54.5 pF.
6
7The crystal has a nominal tolerance of 15 ppm at 25 C plus a temperature
8tolerance of 15 ppm. The following deviations from 1 MHz at CLKM were
9measured with the CNTR board, roughly at 20-25 C:
10
11Board Error Meas. accuracy C14/C15 Trim
12        (f, ppm) (ppm, nom.) (pF) (pF)
13--------------- --------------- --------------- ------------ --------
142, "orange" +268 99.6 NC 0
15        +266 99.5 NC 0
16        +266 40.0 NC 0
17        +148 99.8 NC 3.0
18        +147 99.7 NC 3.0
19        +147 40.0 NC 3.0
20        +111 100.0 NC 4.5
21        +110 99.8 NC 4.5
22        - 13 99.9 15 0
23        - 14 100.0 15 0
24        + 11 99.9 12 0
25        + 11 99.6 12 0
26(cleanup) + 14 100.0 12 0
27        + 14 100.0 12 0
28
291, "red" +263 99.7 NC 0
30        +263 100.0 NC 0
31        +107 99.3 NC 4.5
32        +108 100.0 NC 4.5
33        + 24 99.8 10 0
34        + 24 100.0 10 0
35        - 9 99.7 10 4.5
36        - 9 100.0 10 4.5
37(cleanup) + 14 100.0 12 0
38        + 14 100.0 12 0
39
40(Multiple measurements to assess CNTR performance and drift. Note that
41CNTR measurements are repeatable within 1 ppm, so the nominal accuracy
42appears to be far too pessimistic.)
43
44These measurements suggest that, combined with parasitic capacitance,
45load capacitors of 12 pF make the crystal roughly half the trim range
46faster than 16 MHz.
47

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