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Solder metal can of a crystal to GND or not?

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RoGeorge:
The quartz is same size as in the picture, but a 20MHz THT, scrapped from a defective HDD (manufactured 1991).  Want to use it instead of the stock 8MHz crystal, to test some software ideas.  Nothing metrology grade, weekend tinkering but with a need for low phase noise.  The lower the clock jitter, the better .



Usually the can is never soldered to GND in production PCBs, but I remember some DIY ham radio gear (hand made) where the metal can of a 2 pins quartz was soldered to GND.  Is that a mistake?

For minimum phase noise/clock jitter, would it help to solder the can to GND?

CaptDon:
Many of my salvaged can crystals had a grounding lead soldered to the can. Most often this was done when there were several oscillators of different frequencies near each other. I have also seen this done if the unit was designed to operate in a noisy environment. In your operational situation I doubt if the grounded or ungrounded difference could be measured but it surely wouldn't hurt to ground it as long as the crystal isn't damaged by heat. During the common TTL crystal oscillators of days gone by if two or more oscillators were next to each other you could see a certain amount of pulling or FM'ing between each other which was about 90% caused by poor power rail decoupling and about 10% do to the traces of each oscillator acting like an antenna picking up signal coming from the adjacent oscillator.

Wallace Gasiewicz:
Lots of Xrals have case soldered to GND. Even in production assembly in old radios.  Lots do not have case soldered to Gnd. Many Xtals  in old Channel radios have one Xtal per channel that is not soldered to Gnd.    Soldering to Gnd helps shield the Xtal from other signals but also can change the capacitance that the metal Xtal case adds to the circuit.

Check the chip first and see if it will support 20 MHZ.. I cannot read the chip number.
The biggest problem I see here is that the circuit the Xtal is it may not support 20 MHZ oscillation.     
I would stick your 20 MHz Xtal in the circuit and see if it works. Otherwise you may have to change the adjoining capacitors to a lower value.   
Apparently you wish to use the entire board but at 20 MHz, otherwise a 20 MHz 4 pin oscillator is very cheap.

RoGeorge:
The MCU is an ATmega328P-AU at 5V, it supports max. 20MHz.

Did the quartz replacement already.  So far the MCU seems to be working fine at 20MHz.  The already existing capacitors are 2 x 20pF (according to the schematic for that 8MHz PCB), but I didn't measure them.

Don't have any instrument to directly measure the phase noise.  Maybe I'll improvise later some counters, and compare the output pulses against another clock generated from a Rigol DG4102 AWG.  The AWG is supposed to have a decent phase noise.  My guess is the AWG should produce a smaller time jitter than the MCU, but I didn't try yet.

Back to the crystal can, in case grounding it doesn't hurt, I'll probably add a 3'rd wire to GND for better mechanical sturdiness.

temperance:
Those old style xtals are very often not soldered to GND. But indeed I have seen it being done and always wondered if it would make a difference. The can of an SMD versions HC49 XTALS can't be soldered to GND because of the plastic base underneath.

But smaller SMD xtals with 4 connections do have two connections which connect the metal top lid and I connect those to GND. You also have variants of those where the housing is ceramic and those two extra connections don't serve any purpose.

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