Will this Circuit fry my Crystals? - Page 1
Forum section: electronics / rf-microwave

author: Fionaa
author_rank: Contributor
timestamp: February 14, 2025, 09:50:03 am
content: Will this circuit fry an max 500 uW Drive Level XTAL?

author: RoGeorge
author_rank: Super Contributor
timestamp: February 14, 2025, 11:48:57 am
content: I don't think that circuit can fry a 8MHz quartz (but I never tested it).The ones that require special attention are the 32768Hz resonators (those from quartz clocks and wrist watches), because the 32k crystals are shaped like tuning forks, they do bend while oscillating, and if you overdrive them they can break. Somebody filmed that with stroboscopic lights:In-phase mode of a quartz tuning forkCastellanos-Gomez LabAnti-phase oscillation of a quartz tuning forkCastellanos-Gomez LabHigher frequency quartz resonators, like the 8MHz one in that schematic, are usually made of a solid sheet of crystal shaped like a disk, they don't move visibly.

author: coppercone2
author_rank: Super Contributor
timestamp: February 15, 2025, 03:35:03 am
content: Maybe what happens with those is they get hot and then break, because you can destroy a piezo element, but those get pretty hot before they break. I think you would need a power oscillator to do that pulling some pretty high current. I think it would take many wattsIf you hook up a crystal to a function generator it can make noise IIRC, disk caps do it easily. I imagine it would be somewhat similar requirements to breaking a disk capacitor. And the drive level might arc over, meaning you need some kind of special setup to actually power it at such a high level

author: loulou31
author_rank: Contributor
timestamp: February 15, 2025, 06:13:44 pm
content: Hi, I think that this circuit is not correct The gate is opened in DC?Jean-Louis

author: TimFox
author_rank: Super Contributor
timestamp: February 15, 2025, 09:17:30 pm
content: Normally, one installs a resistor from the FET’s gate to either the FET’s source or ground to bias the gate.

author: Fionaa
author_rank: Contributor
timestamp: February 16, 2025, 03:37:07 pm
content: Yes, i forgot to add it

author: coppercone2
author_rank: Super Contributor
timestamp: February 16, 2025, 08:43:51 pm
content: a reasonator is just a compliant mounted disk capacitor

author: LaserSteve
author_rank: Super Contributor
timestamp: February 18, 2025, 06:19:28 pm
content: Reasonators are generally soft mounted in skulls and odds of damage are low.Quartz resonator circuits for microprocessors often are tested by inserting a low inductance miniature potentiometer in series with the crystal. An alternative is a series of individual resistors, starting high ( >2K Ohm) and working downwards noting where till the oscillator is just stable, then finding a second point where the design parameters are met. ST and TI have appnotes on xtal operating points for clocks. Having just went through a redesign for my company on another fellow's marginal oscillator, one should take capacitances and operating point into careful consideration, least ye find yourself running in a chaotic, unstable, mode.The recall to modify 4,000 boards was unpleasant. The design team did not evaluate an ultra-low power oscillator properly, used the data sheet suggestions with an alternative crystal that required a series load resistor and different capacitor values.So, you CAN evaluate your operating point without much in the way of expensive test gear.TI app note SLAA322D and ST App note AN2867 are an interesting read, even if they are based on Pierce Oscillators.OP's oscillator is a FET Colpitts. Please see attached for a good book.Steve

author: Kean
author_rank: Unknown
timestamp: February 18, 2025, 11:53:29 pm
content: Quote from: LaserSteve on February 18, 2025, 06:19:28 pmTook me a moment, but I've only just started my first coffee of the day.

author: TimFox
author_rank: Super Contributor
timestamp: February 19, 2025, 12:12:02 am
content: Quote from: Kean on February 18, 2025, 11:53:29 pmA sufficient impulse can cause a concussion...