Voltage-variable capacitor doesn't work in LTSpice

Jim Thompson · Mar 19, 2015

On Wed, 18 Mar 2015 16:14:44 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Wed, 18 Mar 2015 14:55:54 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

[snip]

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

http://www.analog-innovations.com/TankTest_Greenshot_2015-03-18_16-10-12.jpg

...Jim Thompson

It would be trivial to add tabular data to this model to characterize
a non-linear transducer.

I just need to scratch my head and remember how to have a subcircuit
call external tabular data so I can make it a generalized transducer
model ;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice

Joerg · Mar 19, 2015

On 2015-03-18 2:50 PM, Jim Thompson wrote:

On Wed, 18 Mar 2015 14:44:39 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:15 PM, Jim Thompson wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

[snip]

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

[snip]

I take it you haven't tried my subcircuit?

I have not given up yet but so far I got all kinds of error messages.
The next step would be to try it on an XP machine where I'd have to get
LTSpice going again. XP was IMHO the last known good OS and I've had
error message in other software caused by Windows 7 (meaning they didn't
happen on an XP machine).

What kind of error messages?

If you use the LTspice _symbol_ I made, you need to open the .ASY file
with a text editor and change the path to wherever you've located the
subcircuit definition library.

And there is the first problem. Windows 7 no longer allows writes to the
program directories. Well, it does but secretly stashes them some place
else but then access become an issue. I'll get to the ground of that,
hav to for my CAD as well, just not right now. The usual, swamped in
work plus honey-do stuff.

And, we had to get a Mexican Burger at one of our favorite watering
holes. Along with an Old Republic red ale.

The latest version, on the website, shows how more clearly.

...Jim Thompson

--
Regards, Joerg

http://www.analogconsultants.com/

Jim Thompson · Mar 19, 2015

On Wed, 18 Mar 2015 16:34:10 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2015-03-18 2:50 PM, Jim Thompson wrote:
On Wed, 18 Mar 2015 14:44:39 -0700, Joerg <news@analogconsultants.com
wrote:
[snip]

I have not given up yet but so far I got all kinds of error messages.
The next step would be to try it on an XP machine where I'd have to get
LTSpice going again. XP was IMHO the last known good OS and I've had
error message in other software caused by Windows 7 (meaning they didn't
happen on an XP machine).

What kind of error messages?

If you use the LTspice _symbol_ I made, you need to open the .ASY file
with a text editor and change the path to wherever you've located the
subcircuit definition library.

And there is the first problem. Windows 7 no longer allows writes to the
program directories.

I have LTspice installed in a directory outside of Program Files. I
haven't "upgraded" to Win7 yet. I hope I can still get away with
that.

Well, it does but secretly stashes them some place
else but then access become an issue. I'll get to the ground of that,
hav to for my CAD as well, just not right now. The usual, swamped in
work plus honey-do stuff.

I appreciate the problem ;-)

And, we had to get a Mexican Burger at one of our favorite watering
holes. Along with an Old Republic red ale.

Aha! The most important interruption >:-}

The latest version, on the website, shows how more clearly.

...Jim Thompson

Joerg · Mar 19, 2015

On 2015-03-18 2:55 PM, John Larkin wrote:

On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

--
Regards, Joerg

http://www.analogconsultants.com/

John Larkin · Mar 19, 2015

On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Joerg · Mar 19, 2015

On 2015-03-18 4:38 PM, Jim Thompson wrote:

On Wed, 18 Mar 2015 16:34:10 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:50 PM, Jim Thompson wrote:
On Wed, 18 Mar 2015 14:44:39 -0700, Joerg <news@analogconsultants.com
wrote:
[snip]

I have not given up yet but so far I got all kinds of error messages.
The next step would be to try it on an XP machine where I'd have to get
LTSpice going again. XP was IMHO the last known good OS and I've had
error message in other software caused by Windows 7 (meaning they didn't
happen on an XP machine).

What kind of error messages?

If you use the LTspice _symbol_ I made, you need to open the .ASY file
with a text editor and change the path to wherever you've located the
subcircuit definition library.

And there is the first problem. Windows 7 no longer allows writes to the
program directories.

I have LTspice installed in a directory outside of Program Files. I
haven't "upgraded" to Win7 yet. I hope I can still get away with
that.

Win 7 is a royal pain in the you-know-what. I needed a new PC because of
simulation speed and they didn't offer XP anymore :-(

Well, it does but secretly stashes them some place
else but then access become an issue. I'll get to the ground of that,
hav to for my CAD as well, just not right now. The usual, swamped in
work plus honey-do stuff.

I appreciate the problem ;-)

And, we had to get a Mexican Burger at one of our favorite watering
holes. Along with an Old Republic red ale.

Aha! The most important interruption >:-}

Yeah, but now I have to bicycle lots of extra miles to work off the
calories.

The latest version, on the website, shows how more clearly.

Thanks. I'll still try that but meantime John's version worked on my PC.
It doesn't need any custom symbols. I originally tried it almost the
same way but mine produced error messages while John's doesn't.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg · Mar 19, 2015

On 2015-03-18 4:46 PM, John Larkin wrote:

On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

Yup

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

I think I know what it could have been. I had a voltage rail called "X"
left in the schematic and it must have not liked that.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg · Mar 19, 2015

On 2015-03-18 5:03 PM, Lasse Langwadt Christensen wrote:

Den torsdag den 19. marts 2015 kl. 00.34.08 UTC+1 skrev Joerg:
On 2015-03-18 2:50 PM, Jim Thompson wrote:
On Wed, 18 Mar 2015 14:44:39 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:15 PM, Jim Thompson wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

[snip]

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

[snip]

I take it you haven't tried my subcircuit?

I have not given up yet but so far I got all kinds of error messages.
The next step would be to try it on an XP machine where I'd have to get
LTSpice going again. XP was IMHO the last known good OS and I've had
error message in other software caused by Windows 7 (meaning they didn't
happen on an XP machine).

What kind of error messages?

If you use the LTspice _symbol_ I made, you need to open the .ASY file
with a text editor and change the path to wherever you've located the
subcircuit definition library.

And there is the first problem. Windows 7 no longer allows writes to the
program directories. Well, it does but secretly stashes them some place
else but then access become an issue. I'll get to the ground of that,
hav to for my CAD as well, just not right now. The usual, swamped in
work plus honey-do stuff.

tried right-click "run as administrator" ?

you can put stuff the program directory you just have to copy and say yes to a UAC prompt

I did that and then it put it into some extra directory and marked the
file with a yellow padlock. I can't stand such behavior of an OS that MS
calls "professional".

--
Regards, Joerg

http://www.analogconsultants.com/

Jim Thompson · Mar 19, 2015

On Wed, 18 Mar 2015 16:47:49 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, March 18, 2015 at 1:54:56 PM UTC-4, John Larkin wrote:
On Wed, 18 Mar 2015 17:40:06 +0000 (UTC), DecadentLinuxUserNumeroUno
DLU1@DecadentLinuxUser.org> wrote:

On Wed, 18 Mar 2015 10:30:44 -0700, John Larkin wrote:

On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

Voltage-Controlled Capacitor Spice Model now on my website.

See VControlledCap.zip on the Device Models & Subcircuits Page.

Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG showing
how it was developed.

...Jim Thompson

I don't have time to play with this just now, but one quick question:

Given that C is a variable capacitor, set C to 1F and charge it to 1
volt. Now change C to 0.5F. What is the new voltage?

How many 1 farad capacitors are you aware of?

In LT Spice, you can use any C value. 1F is the generic capacitor. I
usually normalize theoretical circuits to 1F, 1H, 1 ohm. [1]

In real life, Digikey will sell you 1F caps. Or 5000F caps. But not
variable 1F caps.

Oh and would not a 1F charged cap dump into a 0.5F cap and fully charge
it? If that answer is yes, then the voltage would be the same...
slightly less even, all elements considered.

You thought it would morph the EMF into something else?

I'd like to know if Jim's model conserves charge, or conserves energy,
or conserves voltage. Or whatever it does.
Well, energy conservation seems silly... if you are changing C,
moving plates around, someone has to provide the energy.
And I assume charge or voltage depends on how it's hooked up.

George H.

[1] I do find myself picking standard values, like 39nF instead of 40
nF, and worrying about leakage and stray capacitance and power
dissipation, when none of these matter in Spice.

The simulation I posted ala Joerg's transducer demonstrates energy
changes (AM modulation) and the FM modulation you'd expect from the
capacitor changing value.

I'm musing how to set up an old fashioned "pump" frequency multiplier
;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice

Ralph Barone · Mar 19, 2015

Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

[snip]

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

[snip]

I take it you haven't tried my subcircuit?

...Jim Thompson

Jim, can I assume that your subcircuit switches capacitance between two
values based on a voltage? I suspect Joerg's desire is for something that
is a mite less "binary".

Ralph Barone · Mar 19, 2015

John Larkin <jlarkin@highlandtechnology.com> wrote:

On Wed, 18 Mar 2015 18:54:11 +0000, Syd Rumpo <usenet@nononono.co.uk
wrote:

On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Cheers

Q is charge and X is the cap voltage.

Q = (expression) * X

just means that (expression) is the capacitance. Seems silly to me.

http://ltwiki.org/LTspiceHelp/LTspiceHelp/C_Capacitor.htm

I tried a capacitor that changes value abruptly at 0 volts, like the
example. That works. If I try to change C abruptly at a non-zero
voltage, the sim crashes. Some conservation thingie was violated.

Which is where I was heading with my question about conservation of charge.
Perhaps changing the capacitance breaks something inside the sim related to
continuity of charge.

Jasen Betts · Mar 19, 2015

On 2015-03-18, DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote:

On Wed, 18 Mar 2015 10:30:44 -0700, John Larkin wrote:

On Wed, 18 Mar 2015 09:28:57 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

Voltage-Controlled Capacitor Spice Model now on my website.

See VControlledCap.zip on the Device Models & Subcircuits Page.

Includes Library File (.LIB), LTspice Symbol (.ASY), and a JPEG showing
how it was developed.

...Jim Thompson

I don't have time to play with this just now, but one quick question:

Given that C is a variable capacitor, set C to 1F and charge it to 1
volt. Now change C to 0.5F. What is the new voltage?

How many 1 farad capacitors are you aware of?

I've seen maybe 10 or 20 examples for sale retail. seen adverts for more.

Oh and would not a 1F charged cap dump into a 0.5F cap and fully charge
it? If that answer is yes, then the voltage would be the same...
slightly less even, all elements considered.

"change", not "charge"

> You thought it would morph the EMF into something else?

conservation of matter and all that.

--
umop apisdn

John Larkin · Mar 19, 2015

On Wed, 18 Mar 2015 17:05:28 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2015-03-18 4:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

Yup

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

I think I know what it could have been. I had a voltage rail called "X"
left in the schematic and it must have not liked that.

Try this one:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_2.asc

the peak inductor current triples from start to end, so the stored
energy in the tank goes up almost 10:1.

--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

John Larkin · Mar 19, 2015

On Wed, 18 Mar 2015 20:56:51 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Wed, 18 Mar 2015 17:05:28 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 4:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

Yup

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

I think I know what it could have been. I had a voltage rail called "X"
left in the schematic and it must have not liked that.

Try this one:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_2.asc

the peak inductor current triples from start to end, so the stored
energy in the tank goes up almost 10:1.

I you make an instantaneous change in C, LT Spice conserves charge, so
doesn't conserve energy. Spice doesn't need to conserve energy.

--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Joerg · Mar 20, 2015

On 2015-03-19 8:37 AM, John Larkin wrote:

On Wed, 18 Mar 2015 20:56:51 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Wed, 18 Mar 2015 17:05:28 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 4:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

Yup

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

I think I know what it could have been. I had a voltage rail called "X"
left in the schematic and it must have not liked that.

Try this one:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_2.asc

the peak inductor current triples from start to end, so the stored
energy in the tank goes up almost 10:1.

That probably only works in the cyber world

I you make an instantaneous change in C, LT Spice conserves charge, so
doesn't conserve energy. Spice doesn't need to conserve energy.

SPICE has weirdnesses. When I tried to massage the stimulus pulse for
the cap values using LC the capacitor action flatlined. The stimulus
itself looks ok, it's just that the formula in the cap seems to choke.
So I had to restrict it to RC. Beats me why but for now it's good enough.

Thanks again for all the hints. I got it to run and produce a useful WAV
output for the software engineer. 60 cardiac cycles. Ba-bump .. ba-bump
... ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP* .... just
kidding ...

--
Regards, Joerg

http://www.analogconsultants.com/

John Larkin · Mar 20, 2015

On Thu, 19 Mar 2015 13:30:47 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2015-03-19 8:37 AM, John Larkin wrote:
On Wed, 18 Mar 2015 20:56:51 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Wed, 18 Mar 2015 17:05:28 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 4:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 16:39:38 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 2:55 PM, John Larkin wrote:
On Wed, 18 Mar 2015 14:03:07 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 1:46 PM, John Larkin wrote:
On Wed, 18 Mar 2015 13:36:27 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-18 11:54 AM, Syd Rumpo wrote:
On 17/03/2015 00:26, Joerg wrote:
Gentlemen,

Setting up voltage-controlled resistors is easy: R=(V(X)+0.01) or
whatever. Works, always did. Doing the same with a capacitor fails with
this error message:

Error on line 6 : c1 n002 0 c=(v(x)+0.01)
Unable to find definition of model "c"

* Unknown parameter "x"
WARNING: Less than two connections to node X. This node is used by V4.
Fatal Error: Missing capacitance value for "C1"

Both sims attached. What gives? Ideas how to make it work? Disregard the
values that wouldn't make sense for the cap here, this is just to find
the principal reason why the control method doesn't work with capacitors.

snip

This is what I did for a time-varying capacitance. In the component
'Value' field, I put Q=(4p/(0.25 +(time*5)))*x which swept the
capacitance from 16pF downwards controlled by the internal variable 'time'.

I can't remember why you need the Q and the x, but you do, and it took a
good while to find out - it seems you can't just vary the capacitance
directly. Replace time with a voltage and the appropriate scaling and
you should be good to go.

Tried it and that completely bungled the linearity when the cap is
inside a resonant circuit. At least no more error messages which is
good. Well, maybe I just do it in hardware then, firing up the old
Weller. I'd have to buy a bag of varicaps but those are cheap.

Are you trying to sim a VCO? Simulating oscillators is always tedious.

No, it's a circuit where a capacitive sensor is employed and I want to
mimic the sensor output. The capacitor itself will be inside a somewhat
resonant circuit so it has to behave like a real and clean capacitor.

Would something like this work?

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_1.asc

The cap is modulated by voltage ZZ, which in this case makes the cap
ramp from 1F to 20F. That in turn sweeps the LC ringing frequency
down.

Thanks, John, that actually seems to work. Beats me why mine didn't
because the only difference was that I called "ZZ" "Y" instead.

Well, that's what you need an expert for!

Yup

It may matter about whitespace in the Q equation; it doesn't seem to
like any.

Well, I may find this useful in the future.

I think I know what it could have been. I had a voltage rail called "X"
left in the schematic and it must have not liked that.

Try this one:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Caps/Modulated_Cap_2.asc

the peak inductor current triples from start to end, so the stored
energy in the tank goes up almost 10:1.

That probably only works in the cyber world

I you make an instantaneous change in C, LT Spice conserves charge, so
doesn't conserve energy. Spice doesn't need to conserve energy.

SPICE has weirdnesses. When I tried to massage the stimulus pulse for
the cap values using LC the capacitor action flatlined. The stimulus
itself looks ok, it's just that the formula in the cap seems to choke.
So I had to restrict it to RC. Beats me why but for now it's good enough.

Thanks again for all the hints. I got it to run and produce a useful WAV
output for the software engineer. 60 cardiac cycles. Ba-bump .. ba-bump
.. ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP* .... just
kidding ...

This is fun:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Current_Sources/Isink_NAN.asc

LTS doesn't mind zero value resistors or caps, but it doesn't like L=0
in this circuit.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Tom Swift · Mar 20, 2015

Joerg <news@analogconsultants.com> wrote:

[...]

Thanks again for all the hints. I got it to run and produce a useful
WAV output for the software engineer. 60 cardiac cycles. Ba-bump ..
ba-bump .. ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP*
.... just kidding ...

Another method might be to search google for 'heart sounds'. You will
find many examples of normal and abnormal sounds to work with. Find a
site that allows you to download the file in MP3 format, such as

http://depts.washington.edu/physdx/heart/demo.html

A normal heart sounds like

http://depts.washington.edu/physdx/audio/normal.mp3

Download it and listen in VLC to see if it's what you want. Then search
google for MP3 to WAV converters. Watch out for ones that want you to
download a 'download management' file. Skip those ones. There's a good
online site at

http://audioformat.com/mp3-to-wav

In this case, the normal.mp3 file is 154,227 bytes, and the WAV file is
850,220 bytes. There seems to be some mashup at the beginning, but
otherwise it sounds exactly like the MP3 file. You can probably edit it
and trim the part you want or extend it.

You can find all kinds of abnormalities to listen to. I have a young and
very pretty doctor who just gave me a complete physical. I have
absolutely no idea how she can memorize all those different sounds. There
are hundreds of them. But maybe you can put them in your device and have
them detected automatically.

Joerg · Mar 20, 2015

On 2015-03-19 2:55 PM, John Larkin wrote:

On Thu, 19 Mar 2015 13:30:47 -0700, Joerg <news@analogconsultants.com
wrote:

On 2015-03-19 8:37 AM, John Larkin wrote:

[...]

I you make an instantaneous change in C, LT Spice conserves charge, so
doesn't conserve energy. Spice doesn't need to conserve energy.

SPICE has weirdnesses. When I tried to massage the stimulus pulse for
the cap values using LC the capacitor action flatlined. The stimulus
itself looks ok, it's just that the formula in the cap seems to choke.
So I had to restrict it to RC. Beats me why but for now it's good enough.

Thanks again for all the hints. I got it to run and produce a useful WAV
output for the software engineer. 60 cardiac cycles. Ba-bump .. ba-bump
.. ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP* .... just
kidding ...

This is fun:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Current_Sources/Isink_NAN.asc

LTS doesn't mind zero value resistors or caps, but it doesn't like L=0
in this circuit.

But it works if you give the inductor 1 femtohenry. Nothing in the world
could ever have such a low inductance.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg · Mar 20, 2015

On 2015-03-19 3:41 PM, Tom Swift wrote:

Joerg <news@analogconsultants.com> wrote:

[...]

Thanks again for all the hints. I got it to run and produce a useful
WAV output for the software engineer. 60 cardiac cycles. Ba-bump ..
ba-bump .. ba-bump .. ba-bump .. ba-bump ............... *BEEEEEEEEEP*
.... just kidding ...

Another method might be to search google for 'heart sounds'. You will
find many examples of normal and abnormal sounds to work with. Find a
site that allows you to download the file in MP3 format, such as

http://depts.washington.edu/physdx/heart/demo.html

A normal heart sounds like

http://depts.washington.edu/physdx/audio/normal.mp3

Download it and listen in VLC to see if it's what you want. Then search
google for MP3 to WAV converters. Watch out for ones that want you to
download a 'download management' file. Skip those ones. There's a good
online site at

http://audioformat.com/mp3-to-wav

In this case, the normal.mp3 file is 154,227 bytes, and the WAV file is
850,220 bytes. There seems to be some mashup at the beginning, but
otherwise it sounds exactly like the MP3 file. You can probably edit it
and trim the part you want or extend it.

The problem is that I need the aortic pressure signal and not the sound.
I've mimicked it with an asymmetrical RC sawtooth for now, good enough
to test the software initially.

You can find all kinds of abnormalities to listen to. I have a young and
very pretty doctor who just gave me a complete physical. I have
absolutely no idea how she can memorize all those different sounds. There
are hundreds of them. But maybe you can put them in your device and have
them detected automatically.

It comes with experience of maybe she has a knack for it. As a kid I was
pretty good at diagnosing car engine troubles by ear. Until a kablouie
kind of accident in the army messed up my hearing.

Once I told my dad a valve on his new 5-cylinder Audi may be bad,
probably an exhaust valve. So he brought it to the dealer. They laughed.
"Phhht ... it's brand new and besides, what does a kid know?". My dad
insisted. So they did a compression test and sure enough it failed the
test on one cylinder. Major engine tear down and its exhaust valve had a
deep V-cut burned into it from the side, totally toast. It was a
warranty repair.

--
Regards, Joerg

http://www.analogconsultants.com/

Tom Swift · Mar 20, 2015

Joerg <news@analogconsultants.com> wrote:

The problem is that I need the aortic pressure signal and not the
sound. I've mimicked it with an asymmetrical RC sawtooth for now, good
enough to test the software initially.

Cool! That signal appears to be much more complex. Good thing you're doing
it and not me!

Voltage-variable capacitor doesn't work in LTSpice

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