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Teardown of a quartz crystal oscillator and the tiny IC inside

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Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#21

Post by adrian_b »

Trouble_007 wrote: post #15

Two common frequencies used at the introduction of the PC were 3.579545 MHz. & 4.43361875 MHz Chosen because of the existing supply of cheap xtals manufactured for NTSC & PAL color television sets. NTSC : https://en.m.wikipedia.org/wiki/NTSC PAL : https://en.m.wikipedia.org/wiki/PAL Edits to fix typos :( And add; Crystal Oscillator Frequencies : https://en.m.wikipedia.org/wiki/Crystal_oscillator_frequenci...

That is why the IBM PC has used a 14.31818 MHz oscillator, i.e. 4 times the NTSC frequency of 3.579545 MHz, and which divided by 3 provided a clock frequency for the CPU that was close enough to 5 MHz (the maximum clock frequency of the 1st version of Intel 8088).

While the current computers with Intel/AMD CPUs do no longer care about NTSC, all still have a timer equivalent with the Intel 8253, which uses the clock frequency of 14.31818 MHz, to ensure compatibility with the original IBM PC.

Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#23

Post by krallja »

melony wrote: post #6
fake-name wrote: post #4

Earlier quoted context omitted.

It's a function of size. Tuning fork crystals generally have frequencies in the range of a few tens of kilohertz (generally 32768 Hz). Quartz discs vibrate at many megahertz. A tuning-fork like structure that oscillated at 100 MHz would be far to small to easily manufacture. ------ One fun note: crystals like this are used for measuring deposited material in vacuum processes like PVD [1] or similar [2]. The crystal i…

Note 32768 Hz is chosen because it is a power of 2 (the 15th power).

The first power of two that is outside the range of (most) human hearing.

Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#24

Post by ncmncm »

I think the first paragraph explaining the oscillator operation is not quite right. Corrected, below, maybe. I swapped "increases" and "decreases". But the fix might be something different.

"In more detail, as the voltage across the crystal decreases, the transistor turns on, feeding current into the capacitors and boosting the voltage across the capacitors (and thus the crystal). But as the voltage across the crystal increases, the transistor turns off and the current sink (circle with arrow) pulls current out of the capacitors, reducing the voltage across the crystal. Thus, the feedback from the drive transistor strengthens the crystal's oscillations to keep them going."

Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#25

Post by kens »

ncmncm wrote: post #24

I think the first paragraph explaining the oscillator operation is not quite right. Corrected, below, maybe. I swapped "increases" and "decreases". But the fix might be something different. "In more detail, as the voltage across the crystal decreases, the transistor turns on, feeding current into the capacitors and boosting the voltage across the capacitors (and thus the crystal). But as the voltage across the crysta…

It's like pushing a swing. You want to give it a push when it's moving forward to keep the oscillation going.

Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#26

Post by jecel »

stephen_g wrote: post #19
varispeed wrote: post #10

Almost 40 years old technology and we are still unable to "print" these dies at home. Can you imagine how much fun that would bring if you could design your own IC and just hit print, then load the die into the carrier and solder the pins? There isn't even a service like JLCPCB where you could get your custom ICs made and shipped to you.

Yes there are services where you can get custom ICs made - they’re called ‘multi project wafer’ services. They start around $10K (e.g. efabless does one about that much with the SkyWater 130 nm proces) which is pretty good given how much it costs to do the lithography, not to mention actually making the ICs! But in general it’s a very difficult process. The cleanliness required, the scale at which all this happens, e…

There are cheaper options than $10K (see Mosis or Europractice price tables) but they have smaller areas (to be cheaper, you can have larger chips if you pay more) and might require commercial tools and NDAs. The process options range from much older than the Skywater one to reasonably recent technologies (with proportionally higher prices).

Re: Teardown of a quartz crystal oscillator and the tiny IC inside

#27

Post by ncmncm »

kens wrote: post #25
ncmncm wrote: post #24

I think the first paragraph explaining the oscillator operation is not quite right. Corrected, below, maybe. I swapped "increases" and "decreases". But the fix might be something different. "In more detail, as the voltage across the crystal decreases, the transistor turns on, feeding current into the capacitors and boosting the voltage across the capacitors (and thus the crystal). But as the voltage across the crysta…

It's like pushing a swing. You want to give it a push when it's moving forward to keep the oscillation going.

I am corrected.
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