Crystal Ringing - Page 1
Forum section: electronics / beginners

author: Helder22
author_rank: Contributor
timestamp: November 02, 2014, 10:10:25 pm
content: A friend of mine send me a couple crystals for me to play with so I'm looking at the output wave and Im seeing this ringing after the up-slope. What causes this? Is this from the crystal or something generated by the scope?Ive attached a couple pictures.BTW the scope is a Rigol MSO2072a and the crystal is a 1Mhz.My friend is reading the same or similar ringing on his DS1102e BTW.

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2014, 10:14:44 pm
content: It isn't a crystal but an oscillator.The ringing is caused by the parasitic inductance and capacitance of the wires between the oscillator's output and your oscilloscope probe.

author: kg4arn
author_rank: Unknown
timestamp: November 02, 2014, 10:47:31 pm
content: Quote from: Hero999 on November 02, 2014, 10:14:44 pm+1Try moving the probe cable with your hand while watching the signal on the scope.If the ringing on the observed signal is changing while you do this, then that confirms it is the probe.

author: Helder22
author_rank: Contributor
timestamp: November 02, 2014, 10:56:49 pm
content: Thanks guys,OK, I hooked the probe directly to the output lead of the oscillator and that didn't change anything.When I move the leads with my hands a lot then it does make a very slight change on the ringing, not much though?Is there any way to get rid of this ringing I'm seeing?

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2014, 11:28:04 pm
content: Quote from: Helder22 on November 02, 2014, 10:10:25 pmI wish everybody showed pictures of their measurement technique!The ringing on the edge is caused by your probing technique and is nothing to do with the crystal. Consider that, as a rule of thumb, 1mm of wire (e.g. in the probe ground) has about 1nH inductance. When combined with the capacitance at the probe tip, it forms a resonant circuit where f = 1/(2*pi*sqrt(L*C)). Plug in the values and you will get a value similar to what you see on your scope.How to get rid of it? Shorten the ground lead and reduce the tip capacitance. The only way to lower the capacitance is to use an active probe or low-impedance Z0 probe. To reduce the inductance use the spring ground wire that came with the probe, or a bayonet as in the attachment.See alsohttp://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdfhttp://elektrotanya.com/files/forum/2009/10/e04a036.pdfhttp://emcesd.com/1ghzprob.htm

author: Helder22
author_rank: Contributor
timestamp: November 03, 2014, 12:02:17 am
content: tggzzz,That took care of it almost 100%. Thanks a lot!

author: tggzzz
author_rank: Super Contributor
timestamp: November 03, 2014, 12:33:28 am
content: Good.For bonus points, what load is seen by the output when you are using that scope probe? Hint: it isn't megaohms!

author: Helder22
author_rank: Contributor
timestamp: November 03, 2014, 12:53:59 am
content: easy there Tggzzz, I'm just starting out!

author: w2aew
author_rank: Super Contributor
timestamp: November 03, 2014, 01:33:32 am
content: Quote from: Helder22 on November 03, 2014, 12:53:59 amYou may want to watch these two videos of mine:

author: Helder22
author_rank: Contributor
timestamp: November 03, 2014, 02:16:25 am
content: Very nice videos. Very well explained. Thanks a lot!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 03, 2014, 04:07:21 am
content: And very likely, those remaining bumps are due to absent bypass -- put maybe 0.1uF across the supply pins, as close to the oscillator as possible.Actually, that it's working as well as it is... do those modules have bypass internally? I never looked..Tim

author: Helder22
author_rank: Contributor
timestamp: November 07, 2014, 05:05:38 pm
content: Here is a shot of the insides

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 07, 2014, 08:27:43 pm
content: Anyone willing to bet it's a 74HC2G14, too?Note to self: don't bother with cans, just buildthe exact same thingon board.Although the higher frequency ones, using overtone crystals, will at least have the LC tuning covered for you (an LC network is required to select the overtone, otherwise instead of e.g. 100.000MHz you get 33.34MHz or something like that -- and no, overtones aren't perfect harmonics, so that's no typo).Tim

author: diyaudio
author_rank: Frequent Contributor
timestamp: November 07, 2014, 10:56:58 pm
content: Quote from: Helder22 on November 02, 2014, 10:10:25 pmI'm surprised some people can probe and get an almost clean waveform using a breadboard, the adjacent dialectic is a about +/- 2 pico farads and influences measurements.I generally wont trust high frequency measurements using a breadboard. breadboard for low frequency analysis and measurements.

author: tggzzz
author_rank: Super Contributor
timestamp: November 07, 2014, 11:28:27 pm
content: Quote from: diyaudio on November 07, 2014, 10:56:58 pmI don't trust breadboard for low frequency circuits - too much chance of broken wires and subtly bad contactsHigh frequency - how lucky are you feeling today?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 08, 2014, 02:43:39 am
content: Quote from: diyaudio on November 07, 2014, 10:56:58 pmWell, so?How are you not going to get an "almost clean waveform" just because there's 2pF to nearby bits of metal (that aren't even immediately connected)?Parroting overly generalized rules of thumb only serves to obscure one's vision. Actually analyzing the situation is far more productive.I've done perfectly serviceable breadboardings, such as ~MHz switching converters. Layout is more tricky, but it's not like RF where you get burned by small signal coupling (for which you have little choice besides ground plane and shield boxes).Tim

author: diyaudio
author_rank: Frequent Contributor
timestamp: November 08, 2014, 10:47:00 am
content: Quote from: T3sl4co1l on November 08, 2014, 02:43:39 amQuoteYes, that's my point. but hey if it works for you then good for you.

author: rob77
author_rank: Super Contributor
timestamp: November 08, 2014, 12:23:23 pm
content: Quote from: T3sl4co1l on November 07, 2014, 08:27:43 pmunless you show me how to divide by 16 using 2 Schmidt trigger inverters, then i'm betting against your bet

author: Zero999
author_rank: Super Contributor
timestamp: November 08, 2014, 06:30:06 pm
content: Quote from: rob77 on November 08, 2014, 12:23:23 pmI noticed that too. I wonder what IC it is?Still, 1MHz crystals are cheap and the CD4060 is a good divider if necessary.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 08, 2014, 09:06:06 pm
content: Oh yeah, it does say 16... nevermindCould be a proper clock generator of some description... or... even a damned microcontroller, hey, how would you know right?Tim

author: daveshah
author_rank: Unknown
timestamp: November 08, 2014, 09:07:20 pm
content: The chip appears to be from the NJU63xx series, based on the pinout and '63' on the package, but I can't find one in SOT-23-6 with a /16 option.