Forums

capacitor nonlinearity again

Started by John Larkin May 9, 2013
Does anybody have an LT Spice example that models the C-V dependence of a
ceramic cap? I was thinking about the parametric frequency divider that I did
with a diode, and it occurs to me that a capacitor's c (probably) falls off
symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based
parametric divider is different.

It might be fun to play with that.


-- 

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
On 5/9/2013 12:08 AM, John Larkin wrote:
> > Does anybody have an LT Spice example that models the C-V dependence of a > ceramic cap? I was thinking about the parametric frequency divider that I did > with a diode, and it occurs to me that a capacitor's c (probably) falls off > symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based > parametric divider is different. > > It might be fun to play with that. >
Isn't capacitor voltage dependence relatively slow physical effect ? VLV
Should be pretty easy to take the standard nonlinear inductor model and 
swap out integral(V dt) for integral(I dt).

Everything else is the same, including "core" loss.  There should still be 
a cutoff frequency where losses take over.  Let's see, eddy current 
becomes "eddy voltage", but not "eddy", which implies a parallel loop, it 
has to be in series now.  That would be the voltage dropped across the 
ESR.  Should be easy to estimate from Z plots, as well as ESL.

Anything you can do with a saturable reactor you can do with a saturable 
cap, obviously.  It'll be smaller, but probably comparable loss, given the 
low Q of type 2 ceramics.

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in 
message news:qgbmo810a6hsg31pk3b0hg11hhuq5cndm6@4ax.com...
> > Does anybody have an LT Spice example that models the C-V dependence of > a > ceramic cap? I was thinking about the parametric frequency divider that > I did > with a diode, and it occurs to me that a capacitor's c (probably) falls > off > symmetrically with +- voltage, but a diode is asymmetric. So the > capacitor based > parametric divider is different. > > It might be fun to play with that. > > > -- > > John Larkin Highland Technology Inc > www.highlandtechnology.com jlarkin at highlandtechnology dot com > > Precision electronic instrumentation > Picosecond-resolution Digital Delay and Pulse generators > Custom timing and laser controllers > Photonics and fiberoptic TTL data links > VME analog, thermocouple, LVDT, synchro, tachometer > Multichannel arbitrary waveform generators
On 2013-05-09 07:08, John Larkin wrote:
> > Does anybody have an LT Spice example that models the C-V dependence of a > ceramic cap? I was thinking about the parametric frequency divider that I did > with a diode, and it occurs to me that a capacitor's c (probably) falls off > symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based > parametric divider is different. > > It might be fun to play with that. > >
Maybe a series connection of a normal capacitor and a behavioral voltage source. Make the voltage of the BV k times an odd power of the voltage across the capacitor. Jeroen Belleman
On Thu, 09 May 2013 00:26:27 -0500, Vladimir Vassilevsky <nospam@nowhere.com>
wrote:

>On 5/9/2013 12:08 AM, John Larkin wrote: >> >> Does anybody have an LT Spice example that models the C-V dependence of a >> ceramic cap? I was thinking about the parametric frequency divider that I did >> with a diode, and it occurs to me that a capacitor's c (probably) falls off >> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >> parametric divider is different. >> >> It might be fun to play with that. >> > >Isn't capacitor voltage dependence relatively slow physical effect ?
It's fast enough to cause distortion at audio frequencies, but it does seem to be very, very messy. This guy did a lot of testing... http://www.cliftonlaboratories.com/capacitor_voltage_change.htm -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On 5/9/2013 8:50 AM, John Larkin wrote:
> On Thu, 09 May 2013 00:26:27 -0500, Vladimir Vassilevsky <nospam@nowhere.com> > wrote: > >> On 5/9/2013 12:08 AM, John Larkin wrote: >>> >>> Does anybody have an LT Spice example that models the C-V dependence of a >>> ceramic cap? I was thinking about the parametric frequency divider that I did >>> with a diode, and it occurs to me that a capacitor's c (probably) falls off >>> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >>> parametric divider is different. >>> >>> It might be fun to play with that. >>> >> >> Isn't capacitor voltage dependence relatively slow physical effect ? > > It's fast enough to cause distortion at audio frequencies, but it does seem to > be very, very messy. > > This guy did a lot of testing... > > http://www.cliftonlaboratories.com/capacitor_voltage_change.htm
This guy assumes capacitor nonlinearity to be static; while it is time dependent effect. That's why his simulations don't match with his own measurements. I'd model capacitor nonlinearity by gyrator with lowpass in control path. First order approximation would probably be enough for practical purpose. Vladimir Vassilevsky DSP and Mixed Signal Designs www.abvolt.com
On Thu, 09 May 2013 09:15:36 -0500, Vladimir Vassilevsky
<nospam@nowhere.com> wrote:

>On 5/9/2013 8:50 AM, John Larkin wrote: >> On Thu, 09 May 2013 00:26:27 -0500, Vladimir Vassilevsky <nospam@nowhere.com> >> wrote: >> >>> On 5/9/2013 12:08 AM, John Larkin wrote: >>>> >>>> Does anybody have an LT Spice example that models the C-V dependence of a >>>> ceramic cap? I was thinking about the parametric frequency divider that I did >>>> with a diode, and it occurs to me that a capacitor's c (probably) falls off >>>> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >>>> parametric divider is different. >>>> >>>> It might be fun to play with that. >>>> >>> >>> Isn't capacitor voltage dependence relatively slow physical effect ? >> >> It's fast enough to cause distortion at audio frequencies, but it does seem to >> be very, very messy. >> >> This guy did a lot of testing... >> >> http://www.cliftonlaboratories.com/capacitor_voltage_change.htm > >This guy assumes capacitor nonlinearity to be static; while it is time >dependent effect. That's why his simulations don't match with his own >measurements. > >I'd model capacitor nonlinearity by gyrator with lowpass in control >path. First order approximation would probably be enough for practical >purpose. > >Vladimir Vassilevsky >DSP and Mixed Signal Designs >www.abvolt.com >
Or use a table, as in... http://www.analog-innovations.com/VVC.zip but, as you suggest, add a low-pass "driving" the table. You could likewise tabularize the dissipation factor. Wonder how you would go about characterizing the "frequency response"? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Thu, 09 May 2013 09:15:36 -0500, Vladimir Vassilevsky <nospam@nowhere.com>
wrote:

>On 5/9/2013 8:50 AM, John Larkin wrote: >> On Thu, 09 May 2013 00:26:27 -0500, Vladimir Vassilevsky <nospam@nowhere.com> >> wrote: >> >>> On 5/9/2013 12:08 AM, John Larkin wrote: >>>> >>>> Does anybody have an LT Spice example that models the C-V dependence of a >>>> ceramic cap? I was thinking about the parametric frequency divider that I did >>>> with a diode, and it occurs to me that a capacitor's c (probably) falls off >>>> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >>>> parametric divider is different. >>>> >>>> It might be fun to play with that. >>>> >>> >>> Isn't capacitor voltage dependence relatively slow physical effect ? >> >> It's fast enough to cause distortion at audio frequencies, but it does seem to >> be very, very messy. >> >> This guy did a lot of testing... >> >> http://www.cliftonlaboratories.com/capacitor_voltage_change.htm > >This guy assumes capacitor nonlinearity to be static; while it is time >dependent effect. That's why his simulations don't match with his own >measurements. > >I'd model capacitor nonlinearity by gyrator with lowpass in control >path. First order approximation would probably be enough for practical >purpose.
It looks messy enough that it's hardly worth modeling, at least to use in a product. Even if you decide it's safe, the next batch of caps may be worse. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
John Larkin <jjlarkin@highnotlandthistechnologypart.com> wrote:
> On Thu, 09 May 2013 00:26:27 -0500, Vladimir Vassilevsky <nospam@nowhere.com> > wrote: > >>On 5/9/2013 12:08 AM, John Larkin wrote: >>> >>> Does anybody have an LT Spice example that models the C-V dependence of a >>> ceramic cap? I was thinking about the parametric frequency divider that I did >>> with a diode, and it occurs to me that a capacitor's c (probably) falls off >>> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >>> parametric divider is different. >>> >>> It might be fun to play with that. >>> >> >>Isn't capacitor voltage dependence relatively slow physical effect ? > > It's fast enough to cause distortion at audio frequencies, but it does seem to > be very, very messy. > > This guy did a lot of testing... > > http://www.cliftonlaboratories.com/capacitor_voltage_change.htm
very nice page there. mylar wins! I should send that guy some polypropylene, polycarbonate and polystyrene caps to test.
On Thu, 09 May 2013 14:32:21 +0200, Jeroen <jeroen@nospam.please>
wrote:

>On 2013-05-09 07:08, John Larkin wrote: >> >> Does anybody have an LT Spice example that models the C-V dependence of a >> ceramic cap? I was thinking about the parametric frequency divider that I did >> with a diode, and it occurs to me that a capacitor's c (probably) falls off >> symmetrically with +- voltage, but a diode is asymmetric. So the capacitor based >> parametric divider is different. >> >> It might be fun to play with that. >> >> > >Maybe a series connection of a normal capacitor and a behavioral >voltage source. Make the voltage of the BV k times an odd power >of the voltage across the capacitor. > >Jeroen Belleman
G source, output in parallel with the capacitor, output current made a function of both the current thru the capacitor and the voltage across it. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.