[SI-LIST] Re: Capacitor spice models which include dielectric losses

Hi Wilbur,

Generally spoken, dielectric losses are relevant at "low" frequencies, 
upto a few MHz.
The magnetic domains turn with the electric field, so an alternating field 
will continuously swap the domains: this causes friction => dielectric 
loss.
But these domains are quite slow, so at higher frequencies they are not 
able to folow the fast switching electric field anymore, 
they steadlily vibrate less with higher frequencies and hence dielectric 
losses decrease.
However, these dielectric losses increase with decreasing frequency below 
mentioned frequency.
Dielectric Loss is specified at 1KHz or 100/120 Hz for high cap-values (> 
22uF).
Above 1 MHz the resistance of the terminations/electrodes and the 
skin-effect are the main - if not the only - contribution on the 
capacitor's losses

The capacitor's ESR (equivalent series resistance, including dielectric 
loss, resistance and skinn effect) will show a "bathtub" 
response when plotted against log-frequency, with it's minimum at moderate 
frequencies (several MHz).
The skin-effect contribution increases wih slope 0.5: it is proportional 
with square root of frequency.
Normally such high-capacitance parts exhibit very low ESR (a few milliOhm) 
at several MHz - and even at higher frequencies -, 
so damping of resonances will be quite unlikely.
To me it is unclear how dielectric losses can be beneficial for reducing 
power plane resonances, because these are at much higher frequencies I 
think.
I never saw an explanation on this, I also only heard that it would be 
benficial.

We have a software program called "MLCCSpice" which simulates Ceramic 
Multilayer Caps (based on measured data).
and also takes in account the dielectric losses. It can save the data to 
S-parameter files.
Unfortunately hi-caps are not included yet.
URL: http://www.yageo.com (click on Poducts) and look for MLCCSpice.

regards, 
Bart Bouma




I am looking for some spice models of ceramic bypass capacitors, 0402, 
0603,
0805, 1210, using various dielctrics.

I notice that the Yaiyo Yuden specs say that the dielectric losses are in
the 16% (size 1210, 100uf/6.3v) to 20% (size 0402 1.0uf/6.3v) range for 
the
high value low voltage parts. These high losses would seem to be very
beneficial in reducing power plane resonances.

I have been trying to find some good capacitor spice models which included
the specific package parasitics as well and the high dielectric losses, 
but
I haven't been able to find them so far. 

Wilbur Harvey - Engineer
Spirent Communications Inc., www.adtech-inc.com
First Hawaiian Center, 999 Bishop St.. Suite 1700
Honolulu, HI 96813
Tel: +1 (808) 440 3494, +1 (808) 440 3363 (Direct)
Mobile: +1 (808) 221 0395
email: wilbur.harvey@xxxxxxxxxxxxxx

 
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