IEEE 802.15.4 subsystem
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IEEE 802.15.4 subsystem Commit Details
Date: | 2010-09-10 05:06:33 (13 years 6 months ago) |
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Author: | Werner Almesberger |
Commit: | df071c3398fed1aa6a3a64eea67b2d4b3a1f993d |
Message: | New ECN about clock circuit of atusd boards. Measured (absence of)
effect of adding an inductor to the clock line. - ecn/INDEX, ecn/ecn0005.txt: new ECN discussing the switch to a capacitative clock voltage divider. With frequency measurements. - atusd/tests/send-20100910: measurement of transceiver performance when placing an inductor in the 16 MHz clock line. |
Files: |
atusd/tests/send-20100910 (1 diff) ecn/INDEX (1 diff) ecn/ecn0005.txt (1 diff) |
Change Details
atusd/tests/send-20100910 | ||
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1 | Same test setup as for send-20100909. Board 100908-A was modified to have | |
2 | a 220 nH inductor in the C7 position, instead of a 0R resistor. | |
3 | ||
4 | Distant Local | |
5 | --------------- --------------- --------------- | |
6 | 100813-red 100813-orange 100908-A (with inductor) | |
7 | ||
8 | TX 255, -91 255, -85 | |
9 | TX 255, -90 255, -85 | |
10 | TX 255, -91 - | |
11 | TX 255, -90 255, -85 | |
12 | TX 255, -91 garbled | |
13 | ||
14 | - TX 255, -47 | |
15 | - TX 255, -47 | |
16 | - TX 255, -47 | |
17 | - TX 255, -47 | |
18 | garbled (-90) TX 255, -47 | |
19 | ||
20 | 255, -82 255, -43 TX | |
21 | 255, -82 255, -43 TX | |
22 | 255, -82 255, -43 TX | |
23 | 255, -82 255, -43 TX | |
24 | 255, -82 255, -43 TX | |
25 | ||
26 | Control experiment: | |
27 | ||
28 | 100813-red 100813-orange 100908-B (unmodified) | |
29 | ||
30 | TX - 255, -83 | |
31 | TX garbled (-91) 255, -86 | |
32 | TX - 255, -86 | |
33 | TX garbled (-91) 255, -86 | |
34 | TX - 255, -86 | |
35 | ||
36 | 255, -83 255, -43 TX | |
37 | 255, -84 255, -43 TX | |
38 | 255, -85 255, -43 TX | |
39 | 255, -84 255, -43 TX | |
40 | 255, -84 255, -43 TX | |
41 | ||
42 | ||
43 | Summary | |
44 | ------- | |
45 | ||
46 | Direction No inductor (1) With ind. (2) Change | |
47 | ------------------------------- --------------- ------------ ------ | |
48 | 100813-red -> 100813-orange 255, -87 255, -91 -4 dB | |
49 | 100813-red -> 100908-A 255, -88 255, -85 +3 dB | |
50 | 100908-A -> 100813-red 255, -85 255, -82 +3 dB | |
51 | ||
52 | 100813-red -> 100813-orange 255, -90 - ? | |
53 | 100813-red -> 100908-B 255, -90 255, -86 +4 dB | |
54 | 100908-B -> 100813-red 255, -87 255, -84 +3 dB | |
55 | ||
56 | (1) Data from send-20100909 | |
57 | (2) Only 100908-A was modified. Changes in the measurements with | |
58 | 100908-B show inaccuracies of the test setup. | |
59 | ||
60 | ||
61 | Conclusion | |
62 | ---------- | |
63 | ||
64 | The differences observed are the same for the modified 100908-A board | |
65 | and the unmodified 100908-B board. The inductor therefore does not seem | |
66 | to have a significant effect on transceiver performance. |
ecn/INDEX | ||
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4 | 4 | 0002 Done Add load capacitors to 16 MHz crystal |
5 | 5 | 0003 Edit Replace balun and filter with integrated balun |
6 | 6 | 0004 Edit Take into account layout considerations for RF |
7 | 0005 Edit Correct atusd clock voltage divider |
ecn/ecn0005.txt | ||
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1 | Correct atusd clock voltage divider | |
2 | ||
3 | ||
4 | According to section 9.6.3 of the data sheet, an external clock supplied | |
5 | to the AT86RF230 has a minimum peak-to-peak voltage of 400 mV and a | |
6 | maximum of only 500 mV. Furthermore, the signal must be DC-free. | |
7 | ||
8 | The voltage divider in the 20100903 and 20100908 designs is too sensitive | |
9 | to interference and the PLL constantly unlocks, rendering the device | |
10 | dysfunctional. | |
11 | ||
12 | A more robust divider circuit can be obtained with the following | |
13 | replacements: C7 -> 0R, R3 -> 33 pF, R4 -> 220 pF. After reworking the | |
14 | 20100908 boards, they no longer suffer PLL unlocks. | |
15 | ||
16 | A Qucs simulation of the circuit can be found in ../atusd/sim/cdiv.sim | |
17 | ||
18 | Frequency measurements yield the following results: | |
19 | ||
20 | Host Board Error Meas. accuracy | |
21 | (f, ppm) (ppm, nom.) | |
22 | ------- --------------- --------------- --------------- | |
23 | Ben #2 20100908-A +2 99.7 | |
24 | +1 99.6 | |
25 | Ben #1 20100908-A +23 99.7 | |
26 | +24 99.9 | |
27 | Ben #1 20100908-B +24 99.4 | |
28 | +24 99.7 | |
29 | Ben #2 20100908-B +2 99.8 | |
30 | +2 99.9 | |
31 | ||
32 | The Ben's 12 MHz crystal has a tolerance of +/- 30 ppm, which is better | |
33 | than the +/- 40 ppm required by IEEE 802.15.4. | |
34 | ||
35 | What remains to be verified is whether this change causes interferences | |
36 | that may affect transceiver performance and may also violate emission | |
37 | regulations. |