Xtal vs. Resonator

[randy.day]

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.

 

[Tim Wescott]

randy.day wrote:

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.


They're ceramic resonators with built in caps. (you can get them

without caps, too).

Basically they have lower Q than a crystal, have a lower potential
accuracy, and they're less expensive. Since crystal Q's are insanely
high, and since you can often get by with a lower accuracy clock source,
resonators can be very cost effective.

Just be sure you understand your requirements, and the impact on the
system of using a resonator, so you'll know if you can get away with it.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Tim Wescott]

Tim Wescott wrote:

randy.day wrote:
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.


They're ceramic resonators with built in caps. (you can get them
without caps, too).

Basically they have lower Q than a crystal, have a lower potential
accuracy, and they're less expensive. Since crystal Q's are insanely
high, and since you can often get by with a lower accuracy clock source,
resonators can be very cost effective.

Just be sure you understand your requirements, and the impact on the
system of using a resonator, so you'll know if you can get away with it.

I forgot to mention -- they're a little chunk of piezoelectric ceramic,

so they work much the same way that a crystal does.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Joel Koltner]

"randy.day" <randy.day@shaw.cax> wrote in message
news:HlGWk.338$j61.24@newsfe04.iad...

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?

Let me guess... you're looking at resonators for use as microcontroller clock
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.

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).

---Joel

 

[Eeyore]

"randy.day" wrote:

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

 

[Randy Day]

In article <fXGWk.362459$vK2.7314@en-nntp-
03.dc1.easynews.com>, zapwireDASHgroups@yahoo.com says...

"randy.day" <randy.day@shaw.cax> wrote in message
news:HlGWk.338$j61.24@newsfe04.iad...
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?

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!

 

[Joel Koltner]

"Randy Day" <randy.day@shaw.cax> wrote in message
news:MPG.23950bb0ee3c8e4198968e@shawnews.ss.shawcable.net...

So they're ok where ppm accuracy isn't an issue?

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, coming up with the exact loading needed to get
the frequency stamped on the crystal -- although you can cheat and just tell a
xtal manufacturer, "in my circuit at 25C, this '10MHz' crystal is actually
122Hz low... please make me a crystal that'll be exactly 10MHz" --, aging,
etc.)

Note that protocols such as RS-232 are typically entirely happy with up to
5-10% timing errors, which is 50,000-100,000PPM, so ceramic resonators are
just fine if you're using them as a microcontroller clock.

---Joel

 

[Joerg]

Randy Day wrote:

In article <fXGWk.362459$vK2.7314@en-nntp-
03.dc1.easynews.com>, zapwireDASHgroups@yahoo.com says...
"randy.day" <randy.day@shaw.cax> wrote in message
news:HlGWk.338$j61.24@newsfe04.iad...

[...]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Phil Allison]

"Joel Koltner"
"Randy Day"

So they're ok where ppm accuracy isn't an issue?

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

 

[Phil Allison]

"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

 

[Joerg]

Phil Allison wrote:

"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.

Well, yeah, the stuff they use in consumer gear is often the pits. But
crystals in there would probably die even quicker. Back when I designed
my first patient interface (which must never fail during a catheter lab
procedure) I inquired about g-ratings for various resonators and
crystals. Huge difference. Those interfaces often fly off the table when
they clean up the lab because someone tugs on the cable. That is a hard
smack from 3ft onto a tile floor. No resonator failures in over a decade.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Phil Allison]

"Joerg"...

Phil Allison wrote:
"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.


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

 

[Eeyore]

Phil Allison wrote:

** Not relevant to the point.

YOU are not relevant to the point !

 

[Phil Allison]

"Eeysore = Mad Dog Pommy Cunt "

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 cunt.




..... Phil

 

[Joel Koltner]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:6p3q0pF66e6bU1@mid.individual.net...

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.

You can also go the other route... Joerg has mentioned to me that it's pretty
cheap and easy to add a small power resistor to heat up your crystal pretty
quickly to "something well above ambient" with a control loop.

What's your favorite oscillator topology for low phase noise, Phil?