IEEE 802.15.4 subsystem
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IEEE 802.15.4 subsystem Commit Details
Date: | 2010-11-05 02:33:04 (13 years 4 months ago) |
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Author: | Werner Almesberger |
Commit: | 8cb17bb1b3f2f8772eb5305ae0251785a64f0a0a |
Message: | Document that the input circuit does not reach the design frequency
(3 MHz) yet. - cntr/cntr.sch: added warning that input circuit isn't good enough yet - cntr/README: document input circuit problem, with measurement results |
Files: |
cntr/README (1 diff) cntr/cntr.sch (2 diffs) |
Change Details
cntr/README | ||
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66 | 66 | cntr -r && sleep 1 && dfu-util -d 0x20b7:0xcb72 -D cntr.bin |
67 | 67 | |
68 | 68 | |
69 | Known issues (hardware) | |
69 | Known issues (version 2 hardware) | |
70 | --------------------------------- | |
71 | ||
72 | - the input circuit only works up to about 1 MHz. The problem is that | |
73 | we discharge too slowly though the base of Q1, which in turn keeps | |
74 | the transistor turned on too long. | |
75 | ||
76 | An alternative design that sets R2 to zero, adds a 47 Ohm termination | |
77 | resistor in parallel to VR4, and places a 1 kOhm resistor between | |
78 | VR4 and Q1 works up to about 2 MHz, but accepts a lot of HF noise | |
79 | and is very sensitive to the signal amplitude. | |
80 | ||
81 | Some test results with a ~1.8 m RG-174 cable, square wave bursts | |
82 | with a 50% duty cycle and ~ 5 ns raise/fall time: | |
83 | ||
84 | Design Frequency Source amplitude Input amplitude | |
85 | (nominal) (nominal) (measured) | |
86 | ------------ ---------- ---------------- --------------- | |
87 | Original 1 MHz 700 mV ~700 mV | |
88 | Alternative 2 MHz 1.6 V ~800 mV | |
89 | 1 MHz 1.5 V ~750 mV | |
90 | ||
91 | The test consisted of setting the frequency and adjusting the nominal | |
92 | source voltage in increments of 100 mV for the lowest voltage at | |
93 | which which ten consecutive bursts of 50000 cycles each were all | |
94 | received correctly. | |
95 | ||
96 | The source has an output impedance of 50 Ohm, so voltage at the probe | |
97 | input (indicated in the table) is roughly half the nominal source | |
98 | voltage in the alternative design. | |
70 | 99 | |
71 | 100 | - the MMCX connector is hard to solder because of its large thermal |
72 | 101 | capacitance and surface |
cntr/cntr.sch | ||
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1 | EESchema Schematic File Version 2 date Mon Oct 25 18:33:18 2010 | |
1 | EESchema Schematic File Version 2 date Thu Nov 4 21:28:19 2010 | |
2 | 2 | LIBS:power |
3 | 3 | LIBS:device |
4 | 4 | LIBS:conn |
5 | 5 | LIBS:c8051f320 |
6 | 6 | LIBS:mini_usb_b |
7 | 7 | LIBS:usb_a_plug |
8 | LIBS:cntr-cache | |
9 | 8 | EELAYER 24 0 |
10 | 9 | EELAYER END |
11 | 10 | $Descr A4 11700 8267 |
12 | 11 | Sheet 1 1 |
13 | 12 | Title "Arbitrary-precision Counter (3 MHz)" |
14 | Date "25 oct 2010" | |
13 | Date "5 nov 2010" | |
15 | 14 | Rev "2" |
16 | 15 | Comp "Werner Almesberger" |
17 | 16 | Comment1 "" |
... | ... | |
19 | 18 | Comment3 "" |
20 | 19 | Comment4 "" |
21 | 20 | $EndDescr |
21 | Text Notes 8250 1000 0 100 ~ 20 | |
22 | Input circuit has known bugs.\nSee README for details. | |
22 | 23 | NoConn ~ 8400 3800 |
23 | 24 | NoConn ~ 8400 2900 |
24 | 25 | Wire Wire Line |