Timeline for Rectifying failed MCU crystal oscillator design
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Dec 18, 2018 at 22:24 | answer | added | Johnny Egeland | timeline score: 3 | |
| Dec 18, 2018 at 22:07 | vote | accept | Johnny Egeland | ||
| Dec 18, 2018 at 21:13 | history | edited | JRE | CC BY-SA 4.0 |
Fixed random capitalization.
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| Dec 18, 2018 at 21:04 | history | edited | Johnny Egeland | CC BY-SA 4.0 |
added 295 characters in body
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| Dec 18, 2018 at 16:48 | comment | added | analogsystemsrf | Congratualtion on the working oscillator. The reason to have a small region of GROUND under the crystal and its traces, with that GROUNDED foil not used for anything else ---- is to avoid injecting fast spikes into the circuit that will cause upsets to the waveform and cause zero-crossing-timing-errors. This is called jitter (or non-random phase noise). | |
| Dec 18, 2018 at 13:43 | answer | added | Spehro 'speff' Pefhany | timeline score: 4 | |
| Dec 18, 2018 at 12:36 | comment | added | Johnny Egeland | I forgot to mention that the Sine I measure at the osc_out pin has the correct frequency of 25 MHz. I will post pictures of the layout as soon as possible. I am a complete beginner in PCB design, and this is very much "learning by doing for" me. It is also why I request your expert opinion, as the available documentation (on which I've spent many hours reading now) still confuses me and seems both contradicting and stripped of useful details (like expected Vp-p and what happens if you get it wrong). | |
| Dec 18, 2018 at 12:36 | answer | added | Damien | timeline score: 2 | |
| Dec 18, 2018 at 12:28 | history | edited | Johnny Egeland | CC BY-SA 4.0 |
added 192 characters in body
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| Dec 18, 2018 at 11:31 | comment | added | IC_Eng | It seems like you have many problems, in regards the unwanted ground plane you can cut sections of it away using a scalpel/sharp knife and your soldering iron to de-bond the copper from the fiber glass. It won't look pretty, but it will work. Also make sure the capacitor values used for the crystal are correct and a track layout is usually suggested in the crystal data sheet. | |
| Dec 18, 2018 at 10:59 | comment | added | Michael Karas | You could also have a problem with the programming of the clock selection and PLL configuration registers. Unless you have a 1::1 direct comparison with some known working reference board programming is one detail you have to check and double check. | |
| Dec 18, 2018 at 10:56 | comment | added | Michael Karas | I think you are jumping to conclusions when you suspect that the oscillator amplitude is too low. It may very well be that the X1 and X2 pins on the MCU just operate that way. Anyway check the frequency of this signal (preferably the X2 pin) and see if it is near the correct frequency. | |
| Dec 18, 2018 at 10:42 | comment | added | Peter Smith | To get the real frequency you could use a timer and toggle a GPIO on overflow / underflow. In addition, check the output for consistent timing (if it jumps around a bit the oscillator amplitude would definitely be suspect). | |
| Dec 18, 2018 at 10:40 | comment | added | awjlogan | Can you post a picture of your old layout? Whole and zoomed in to the oscillator would be useful :) | |
| Dec 18, 2018 at 10:28 | history | asked | Johnny Egeland | CC BY-SA 4.0 |