[HN Gopher] Teardown of a quartz crystal oscillator and the tiny...
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Teardown of a quartz crystal oscillator and the tiny IC inside
Author : parsecs
Score : 83 points
Date : 2021-02-20 17:46 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| kens wrote:
| Author here for any question :-)
| logbiscuitswave wrote:
| No question here - just wanted to thank you for your always
| well-written and fascinating posts. I'm only a hobbyist with
| electronics but I've learned a lot from your tear downs.
|
| As an aside it never ceases to fascinate me that it's literally
| a tiny slice of quartz being used to create these precise
| timing signals.
| sokoloff wrote:
| Thanks for the article; it took me back to memories of bootleg
| replacing the 40MHz oscillator for a 50MHz on my work's IIsi
| over my boss' objection. Now I have some idea of what was
| inside.
|
| Looking forward to any future work you might do to similarly
| explain the modern PLL oscillators as well as the even more
| modern programmable MEMS oscillators.
| kurthr wrote:
| You mention it at the very end, but any idea why a more complex
| (and presumably expensive) oscillator is used? Maybe
| availability of the IC?
|
| It seems strange unless there is a performance (e.g. voltage
| stability due to stray capacitance sensitivity) advantage. It's
| not like they're worried about IP or litigation.
| kens wrote:
| The different oscillator types have various tradeoffs, so
| maybe this more-complex design was better for this
| application, as you suggest. Since the circuit complexity is
| all on the integrated circuit, the cost difference is
| probably very small.
|
| My other theory when people make strange design choices is
| that patents might be involved.
| chiph wrote:
| Possibly ease of manufacturing because you had fewer unique
| parts to make/keep track of. Also allows market
| segmentation, differentiated by the multiplier and whether
| the disable pin was connected.
| CyberRabbi wrote:
| I saw an eevblog teardown of an oscillator module like this,
| but that was newer, not this old stock.
|
| Question for you. This component is technically not a crystal
| component right? I.e. you can hook the output straight into a
| clock input or anything that accepts a digital signal? There
| are other 2-terminal components where the circuit to drive the
| crystal is external, right?
|
| Are those 2-terminal components literally just electrodes
| attached to a crystal or do they have extra circuitry in them
| as well?
| parsecs wrote:
| (Sorry not Ken but:) Two terminal crystals are pretty much
| just electrodes attached to a crystal. The drive circuitry
| for those are usually integrated in the device
| asyncagrajag wrote:
| When I see an HN link from "righto.com" I reflex-click without
| hesitation. Always fascinating, always learn something (or a
| lot of things). Thank you!
| kamranjon wrote:
| Is this related to why film cameras got crystal sync motors?
| When crystal sync motor runs and you record sound separately in
| a crystal sync sound recorder, do they need to run at same
| frequency to be syncable?
| kens wrote:
| I don't know any more about camera motors than what I just
| read [1], but yes, the quartz crystals keep the motors
| running at the exact same speed. This kept the film camera
| and the magnetic tape recorder synchronized.
|
| A semi-related thing that I find interesting is the
| clapperboard that film makers use at the start of each scene
| they record. I had assumed this was a cliche tradition, but
| it's an effective way to synchronize the film and audio. You
| can see on the film the frame where the clapper closes and
| easily synchronize this with the sudden loud noise in the
| audio.
|
| [1] https://www.filmmaking.net/filmmakers-faq/130/what-is-
| crysta...
| formerly_proven wrote:
| This works for short recordings, but for longer recordings
| explicit continuous sync is needed, almost universally using
| Timecode, because normal quartz oscillators are not precise
| nor stable enough to guarantee single frame accurate sync
| over, say, an hour (which would be 10 ppm or so, 1/3600*30)
| fortran77 wrote:
| Back in the 60s and early 70s, ham radio people used quartz
| crystals that were simply a sliver of crystal mounted in a little
| box with no additional circuitry:
|
| https://i.ebayimg.com/images/g/VmAAAOSwdjZfEVOx/s-l640.jpg
|
| A common circuit called a "Pierce Oscillator" (as Ken described
| in this article) was used to enable their oscillating ability:
|
| https://en.wikipedia.org/wiki/Pierce_oscillator
|
| Now all of this comes in a can which is more of a "clock module"
| than a quartz crystal, as Ken Sherriff explained.
| mensetmanusman wrote:
| It's great knowing our grandparents were designing these things
| before we were born.
| CyberRabbi wrote:
| The more I learn about historical technology, the more I see
| that the complexity of logic built on top of old processes
| seems to be about equivalent to the complexity of contemporary
| software systems.
|
| The only thing that seems to be really changing is the
| technological substrate underneath. It leads me to wonder if
| manufacturing ability and materials engineering are really
| what's driving higher order improvements in technology, not
| "algorithms" so to speak. Electrical and mechanical engineers
| of olde otherwise seem to be no less capable of designing
| complex systems than software engineers.
| rafiki6 wrote:
| It's a very interesting positive feedback cycle. Application
| identified. Some manufacturing process gets developed to
| automate. Scale up production. Challenges in scaling process
| are discovered and improvements are made with new tools made
| by manufacturing process. And so forth it goes. See DevOps
| for the software analogue.
| trynton wrote:
| @CyberRabbi
|
| Given the way most modern software is made, refering to the
| makers as "software engineers" is a bit of an exaggeration.
| If you could visualize the average software project, a Rube
| Goldberg machine consisting of cogs, wheels, relays and
| bricks-and-pipes, all held together with duct tape.
| vkdelta wrote:
| Thank you for detailed post. Lot of it taken for granted when
| seeing schematics and it is tiny component named "XO" by
| designers.
| tedd4u wrote:
| If you're interested in this, watch this [1] very in-depth 1943
| movie called "Crystals go to War" which documents crystal
| oscillator manufacturing step by step. Honestly, I was amazed by
| this. I tend to think of technology as pretty primitive in the
| 40s but this is a great reminder of how sophisticated technology
| could be even back then.
|
| [1] https://www.youtube.com/watch?v=fKprsCNLUlE
| kens wrote:
| That's an amazing video. I was surprised by how many steps it
| took to make a crystal. Also noteworthy is how many different
| tests and checks they did on each crystal.
|
| The technology is an interesting mixture of sophisticated and
| primitive. On the one hand, they had X-ray machines to
| determine the crystal alignment, and lots of specialized
| mechanical and electronic machinery. On the other hand, people
| were spooning abrasive out of a pot with a dinner spoon.
| Everything was very manual and labor-intensive, with no
| automation. An interesting mix of highly-skilled precision
| labor and low-skill tasks.
| mhh__ wrote:
| By the end of the second world war the average Lancaster bomber
| was flying with beam navigation, air to ground radar, air to
| air radar, electronic counter-measures etc.
|
| They had pretty similar ideas to us, we can just make things
| smaller.
| tlb wrote:
| I just spent some time understanding the shape of the quartz
| crystal (don't be fooled by the broken disk in the picture -- it
| was originally a circular disk.)
|
| I expected a tuning fork shape. Which indeed are used for low-
| frequency crystals like 32 kHz.
|
| This one is a disk that vibrates in shear mode. The crystal is
| cut on an angle (about 35 degrees) to the crystal grain
| structure. When voltage is applied across the thickness of the
| disk, it creates a force parallel to the crystal axis. The
| crystal is extremely stiff in compression, so it can't get
| thinner, but it can shear so the top moves one way and the bottom
| moves the other.
|
| The reason behind this complicated setup is that it's the most
| stable over temperature. The stiffness of any material changes
| with temperature, but when you get the angles exactly right the
| changes cancel out.
|
| Further reading:
|
| https://en.wikipedia.org/wiki/Crystal_oscillator#Crystal_str...
| https://www.jauch.com/blog/en/its-all-about-the-angle-the-at...
| kevin_thibedeau wrote:
| A MEMS oscillator might make for a nice teardown as comparison.
| mhb wrote:
| Related - Tuning Fork Clock:
| https://hackaday.io/project/177317-tuning-fork-clock
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(page generated 2021-02-20 23:00 UTC)