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Hi all,
I need a model for an 8Mhz ceramic resonator. Does anyone have one
they can post here? Thanks,
p.
--
The BBC: Licensed at public expense to spread lies.
Thanks, Tim! Should be enough here to get me in the ballpark...A two-terminal resonator model just looks like the spice model for a
crystal, but the motational capacitance is higher, the motational inductance
is lower, and (possibly) the motational resistance is higher as well (all a
consequence of the resonator's lower Q). I would expect the case
capacitance to be roughly the same (i.e. single-digit pF).
I've now emptied my brain on this subject, more astute folks than I will
have to give you typical values, or you will have to measure one yourself.
Measuring your own (or trying to pry the information out of the
manufacturer) is probably the best idea, since quartz is quartz but each
ceramic is going to be up to the whim of the manufacturer.
A crystal model looks like:
----------
| |
--- Cm |
--- |
| |
) Lm |
) ---
) --- Cc
| |
\ |
/ Rm |
\ |
/ |
| |
---------
where Cm = motational capacitance, ~ femto (or atto) farads, Lm = motational
inductance ~ henrys, Rm = motational resistance, 10s of ohms, Cc = case
capacitance, 5 - 10pF for "normal" crystals; I don't know about the itty
bitty surface-mount ones.
You can measure Cc directly with a capacitance meter assuming that you're
well away from the resonance frequency. You measure Rm by finding the
effective series resistance at resonance, you deduce Cm and Lm from the
resonance frequency and the Q of the resonator.
The motional inductance is higher and the motional capacitance is lowerA two-terminal resonator model just looks like the spice model for a
crystal, but the motational capacitance is higher, the motational inductance
is lower, and (possibly) the motational resistance is higher as well (all a
consequence of the resonator's lower Q). I would expect the case
capacitance to be roughly the same (i.e. single-digit pF).
--I've now emptied my brain on this subject, more astute folks t----------
| |
--- Cm |
--- |
| |
) Lm |
) ---
) --- Cc
| |
\ |
/ Rm |
\ |
/ |
| |
---------
where Cm = motational capacitance, ~ femto (or atto) farads, Lm = motational
inductance ~ henrys, Rm = motational resistance, 10s of ohms, Cc = case
capacitance, 5 - 10pF for "normal" crystals; I don't know about the itty
bitty surface-mount ones.
You can measure Cc directly with a capacitance meter assuming that you're
well away from the resonance frequency. You measure Rm by finding the
effective series resistance at resonance, you deduce Cm and Lm from the
resonance frequency and the Q of the resonator.
--------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
"Paul Burridge" <pb@osiris1.notthisbit.co.uk> wrote in message
news:mpjv10lkla9hfs9drog84afsdjhup6s8h9@4ax.com...
Hi all,
I need a model for an 8Mhz ceramic resonator. Does anyone have one
they can post here? Thanks,
p.
--
The BBC: Licensed at public expense to spread lies.