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Xtal vs. Resonator

R

randy.day

Jan 1, 1970
0
I noticed some catalog listings for 'resonators', which are portrayed
schematically as a xtal with two included caps to ground.

Are they xtals, or something different, and what are the pros/cons (if any)
over xtals?

Opinions welcome.
 
E

Eeyore

Jan 1, 1970
0
randy.day said:
I noticed some catalog listings for 'resonators', which are portrayed
schematically as a xtal with two included caps to ground.

Optional caps. You can get 'plain ones'.

Are they xtals,

NO. They're Ceramic resonators like the name says.

or something different, and what are the pros/cons (if any)
over xtals?

Ceramic resonators are VASTLY cheaper but do not have the timekeeping tolerance
of crystals. I like resonators since in medium quantities they knock $1.00+ off
the retail price of one's goods..

Graham
 
R

Randy Day

Jan 1, 1970
0
Let me guess... you're looking at resonators for use as microcontroller clock

Heh. Got it in one! :)
references? In that case, no, it's not really a (quartz) crystal (most likely
it's a cermaic resonator -- similar behavior to a crystal, just made out of a
ceramic), and it's drawn the way that it is to show that you don't need the
two capacitors you normally use when you hook a crystal up to the uC's "clock"
pins.

Fair enough...
The pros of ceramic resonators is that they're cheaper... only less than half
the price of a quartz crystal, which in large quantities can be quite
significant. The cons are that they aren't as accurate in frequency and they
have more jitter (due to a lower "Q" or quality factor, if you're familiar
with that).

So they're ok where ppm accuracy isn't an issue?
Useful to know. Thanks!
 
J

Joerg

Jan 1, 1970
0
Randy said:
[...]
The pros of ceramic resonators is that they're cheaper... only less than half
the price of a quartz crystal, which in large quantities can be quite
significant. The cons are that they aren't as accurate in frequency and they
have more jitter (due to a lower "Q" or quality factor, if you're familiar
with that).

So they're ok where ppm accuracy isn't an issue?
Useful to know. Thanks!


Actually there is one more important factor: Resonators can be a lot
more rugged than crystals. I have used them in applications where
frequent falls onto hard surfaces were to be expected. As Joel wrote if
something like RS232 is the most timing-critical aspect on your design
(on many of mine that was the case) you can usually find a resonator
that is precise enough.
 
P

Phil Allison

Jan 1, 1970
0
"Joel Koltner"
"Randy Day"
Yes, absolutely. Their accuracy is usually in the ballpark of some
thousands of PPM (e.g., 2500-10000 PPM), whereas typically quartz crystals
for microcontrollers are 25-100PPM -- two orders of magnitude better --,
although if you're trying to build, e.g., accurate RF oscillators, you can
get quartz crystals as good as 2.5 or even 1PPM.

Actually, once you're in the "handful of PPM" ballpark for accuracy, what
kills you is temperature drift,


** The "tempco" spec for an average crystal is +/- 50ppm, but be aware that
this is for the whole operating temperature range, while the accuracy spec
( typically +/-20ppm) is given at ONE temperature, usually 25C.

This causes lotsa confusion for novices, as the operating temp range can be
70 to 100 degrees C wide.

If you divide the tempco spec by the number of degrees in the operating
range - you come up with a number of about +/-1ppm for the drift per
degree C. In fact, the number may be rather better in the temp range
around 25 C. Plus of course, it is a simple matter to use a trimmer
capacitor adjust the frequency of a crystal oscillator to be "spot on" at a
particular temperature.

So, using only a standard crystal and with an indoor temp that stays within
the range of say 20 to 25 C - one can easily have a crystal oscillator
with an accuracy of a few ppm.

My 1GHz bench frequency counter suffered from an annoying " warm up" drift
of about 25ppm ( due to internal heat coming from the AC tranny and a 5 volt
regulator) until I figured out a simple fix - I just added a 40mm DC fan
blowing outside air DIRECTLY onto the crystal.

Warm up drift is now gone.



...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Joerg"
Actually there is one more important factor: Resonators can be a lot more
rugged than crystals. I have used them in applications where frequent
falls onto hard surfaces were to be expected.


** That is contrary to the experience of folk who repair remote controls for
TVs & DVDs etc.

Failure of ceramic resonators inside them after dropping the devices is VERY
common - particularly the 2 pin kind that operate around 400kHz.



..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Joerg"...
Well, yeah, the stuff they use in consumer gear is often the pits.


** Shame how consumer grade parts ARE what we are discussing.

But crystals in there would probably die even quicker.


** Not relevant to the point.




...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore = Mad Dog Pommy **** "
YOU are not relevant to the point !


** Drunk even before the sun goes over the yard arm ???

Not even a sailor either ......

Just another Rabid Mad Dog pommy ****.




..... Phil
 
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