Parasitic values

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Can anyone tell me how I should be calculating Parasitic Inductance,
Resistance and Capacitance? Any equations would be helpful. I am
revising for a telecommunications module and can't seem to find
anything anywhere and with no answers to work with, I am confused
whether I am doing it right.

Typical question:
A 10.1nH inductor at 1GHz is purely resistive. The measured value of
resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]

eeyvsphREMOVETHIS@nottingham.ac.uk

Thanks all.

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Steve Hill wrote:
>
> Can anyone tell me how I should be calculating Parasitic Inductance,
> Resistance and Capacitance? Any equations would be helpful. I am
> revising for a telecommunications module and can't seem to find
> anything anywhere and with no answers to work with, I am confused
> whether I am doing it right.
>
> Typical question:
> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]

If an inductance (assumed to be a lumped inductance) looks resistive,
then it is being resonated (canceled) at that frequency by an equal
magnitude capacitive impedance. Magnitude of inductive impedance is
2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
them equal and solve for C.

--
John Popelish

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

John Popelish <jpopelish@rica.net> writes:

> Steve Hill wrote:
>>
>> Can anyone tell me how I should be calculating Parasitic Inductance,
>> Resistance and Capacitance? Any equations would be helpful. I am
>> revising for a telecommunications module and can't seem to find
>> anything anywhere and with no answers to work with, I am confused
>> whether I am doing it right.
>>
>> Typical question:
>> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
>> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
>
> If an inductance (assumed to be a lumped inductance) looks resistive,
> then it is being resonated (canceled) at that frequency by an equal
> magnitude capacitive impedance. Magnitude of inductive impedance is
> 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> them equal and solve for C.

The resistance would be irrelevent for this problem, then, but
represents the series resistance of the device.
--
% Randy Yates % "Rollin' and riding and slippin' and
%% Fuquay-Varina, NC % sliding, it's magic."
%%% 919-577-9882 %
%%%% <yates@ieee.org> % 'Living' Thing', *A New World Record*, ELO
http://home.earthlink.net/~yatescr

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

On 22 May 2004 06:45:46 -0700, hill4_steve@yahoo.co.uk (Steve Hill) posted this:

>Can anyone tell me how I should be calculating Parasitic Inductance,
>Resistance and Capacitance? Any equations would be helpful. I am
>revising for a telecommunications module and can't seem to find
>anything anywhere and with no answers to work with, I am confused
>whether I am doing it right.
>
>Typical question:
>A 10.1nH inductor at 1GHz is purely resistive. The measured value of
>resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
>
>eeyvsphREMOVETHIS@nottingham.ac.uk
>
>Thanks all.

Post ALL the questions. We'll give you the answers and you'll ace the
test!

For this one: The only way the inductor can look like a resistor is if
it is resonant at the applied frequency. A resonant circuit will have inductive
and capacitive elements with identical impedances, of opposite signs, of course.
Calculate the impedance of the inductor at the applied frequency and then
calculate a value for the parasitic capacitance that will have the same
impedance at the same frequency. That resistance value given in the question is
either a red herring or the thickness of your skull.

Perhaps you should switch your career goals over to something like
business administration or sales. "Do you want fries with that order, Sir?"

Jim

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

On Sat, 22 May 2004 15:59:18 GMT, James Meyer <jmeyer@nowhere.com>
wrote:

> That resistance value given in the question is
>either a red herring or the thickness of your skull.

Is it? Not for an exact solution, I think. But close enough for the
typical homework problem.

John

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"John Popelish" <jpopelish@rica.net> wrote in message
news:40AF5C11.B3ABB788@rica.net...
| Steve Hill wrote:
| >
| > Can anyone tell me how I should be calculating Parasitic Inductance,
| > Resistance and Capacitance? Any equations would be helpful. I am
| > revising for a telecommunications module and can't seem to find
| > anything anywhere and with no answers to work with, I am confused
| > whether I am doing it right.
| >
| > Typical question:
| > A 10.1nH inductor at 1GHz is purely resistive. The measured value of
| > resistance is 127ohms. Calculate the parasitic capacitance. [2
Marks]
|
| If an inductance (assumed to be a lumped inductance) looks resistive,
| then it is being resonated (canceled) at that frequency by an equal
| magnitude capacitive impedance. Magnitude of inductive impedance is
| 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
| them equal and solve for C.
|
| --
| John Popelish

Is that the same as solving C for XC=127R and F=1GHz.. 1p25?

DNA

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Genome wrote:
>
> John Popelish wrote:

> | If an inductance (assumed to be a lumped inductance) looks resistive,
> | then it is being resonated (canceled) at that frequency by an equal
> | magnitude capacitive impedance. Magnitude of inductive impedance is
> | 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> | them equal and solve for C.
>
> Is that the same as solving C for XC=127R and F=1GHz.. 1p25?

Not at all. If the inductor looks purely resistive, it is the
inductance and capacitance that have canceled each other, leaving
whatever series resistance the inductor had as the only remaining
visible impedance. The value of that resistance really isn't involved
in the calculation of that capacitance. If no inductance remains,
then XC=XL.

--
John Popelish

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"John Popelish" <jpopelish@rica.net> wrote in message
news:40AF6EB9.3CF926CE@rica.net...
| Genome wrote:
| >
| > John Popelish wrote:
|
| > | If an inductance (assumed to be a lumped inductance) looks
resistive,
| > | then it is being resonated (canceled) at that frequency by an
equal
| > | magnitude capacitive impedance. Magnitude of inductive impedance
is
| > | 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
| > | them equal and solve for C.
| >
| > Is that the same as solving C for XC=127R and F=1GHz.. 1p25?
|
| Not at all. If the inductor looks purely resistive, it is the
| inductance and capacitance that have canceled each other, leaving
| whatever series resistance the inductor had as the only remaining
| visible impedance. The value of that resistance really isn't involved
| in the calculation of that capacitance. If no inductance remains,
| then XC=XL.
|
| --
| John Popelish

Aha!, Trick question, like Randy says the resistance is irrelevant.

Thanks

DNA

Guest · May 22, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Genome wrote:
> John Popelish wrote:
> | Genome wrote:

> | > Is that the same as solving C for XC=127R and F=1GHz.. 1p25?
> |
> | Not at all. If the inductor looks purely resistive, it is the
> | inductance and capacitance that have canceled each other, leaving
> | whatever series resistance the inductor had as the only remaining
> | visible impedance. The value of that resistance really isn't involved
> | in the calculation of that capacitance. If no inductance remains,
> | then XC=XL.
> |

> Aha!, Trick question, like Randy says the resistance is irrelevant.
>
> Thanks

That's how I see it. The resistance value (and to 3 digits of
precision, too) is misdirection. I am watching to see if someone else
interprets the problem differently.

--
John Popelish

Guest · May 22, 2004

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"James Meyer" <jmeyer@nowhere.com> wrote in message
news:jhtua0pg1msck4defe4ttdcfmttnk867fe@4ax.com...
| On 22 May 2004 06:45:46 -0700, hill4_steve@yahoo.co.uk (Steve Hill)
posted this:
|
| >Can anyone tell me how I should be calculating Parasitic Inductance,
| >Resistance and Capacitance? Any equations would be helpful. I am
| >revising for a telecommunications module and can't seem to find
| >anything anywhere and with no answers to work with, I am confused
| >whether I am doing it right.
| >
| >Typical question:
| >A 10.1nH inductor at 1GHz is purely resistive. The measured value of
| >resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
| >
| >eeyvsphREMOVETHIS@nottingham.ac.uk
| >
| >Thanks all.
|
| Post ALL the questions. We'll give you the answers and you'll ace the
| test!
|
| For this one: The only way the inductor can look like a resistor is
if
| it is resonant at the applied frequency. A resonant circuit will have
inductive
| and capacitive elements with identical impedances, of opposite signs,
of course.
| Calculate the impedance of the inductor at the applied frequency and
then
| calculate a value for the parasitic capacitance that will have the
same
| impedance at the same frequency. That resistance value given in the
question is
| either a red herring or the thickness of your skull.
|
| Perhaps you should switch your career goals over to something like
| business administration or sales. "Do you want fries with that order,
Sir?"
|
| Jim
|

Well.... I got it wrong......

By the way the correct question is. "Do you want chips with that?"

DNA

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Randy Yates" <yates@ieee.org> a écrit dans le message news:
ekpc8qz2.fsf@ieee.org...
> John Popelish <jpopelish@rica.net> writes:
>
> > Steve Hill wrote:
> >>
> >> Can anyone tell me how I should be calculating Parasitic Inductance,
> >> Resistance and Capacitance? Any equations would be helpful. I am
> >> revising for a telecommunications module and can't seem to find
> >> anything anywhere and with no answers to work with, I am confused
> >> whether I am doing it right.
> >>
> >> Typical question:
> >> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
> >> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
> >
> > If an inductance (assumed to be a lumped inductance) looks resistive,
> > then it is being resonated (canceled) at that frequency by an equal
> > magnitude capacitive impedance. Magnitude of inductive impedance is
> > 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> > them equal and solve for C.
>
> The resistance would be irrelevent for this problem, then, but
> represents the series resistance of the device.

Nope, it's the equivalent parallel resistace of the tank, i.e. Rs*Q^2 (when
Q is high enough).
Here, estimating Q ~ Rp/L*w0 = 127/(10.1*2*pi) = 2 is clearly not enough for
the approximation to hold so you have to do the exact maths.

Thanks,
Fred.

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Fred Bartoli" <fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> writes:

> "Randy Yates" <yates@ieee.org> a écrit dans le message news:
> ekpc8qz2.fsf@ieee.org...
> > John Popelish <jpopelish@rica.net> writes:
> >
> > > Steve Hill wrote:
> > >>
> > >> Can anyone tell me how I should be calculating Parasitic Inductance,
> > >> Resistance and Capacitance? Any equations would be helpful. I am
> > >> revising for a telecommunications module and can't seem to find
> > >> anything anywhere and with no answers to work with, I am confused
> > >> whether I am doing it right.
> > >>
> > >> Typical question:
> > >> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
> > >> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
> > >
> > > If an inductance (assumed to be a lumped inductance) looks resistive,
> > > then it is being resonated (canceled) at that frequency by an equal
> > > magnitude capacitive impedance. Magnitude of inductive impedance is
> > > 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> > > them equal and solve for C.
> >
> > The resistance would be irrelevent for this problem, then, but
> > represents the series resistance of the device.
>
>
> Nope, it's the equivalent parallel resistace of the tank, i.e. Rs*Q^2 (when
> Q is high enough).
> Here, estimating Q ~ Rp/L*w0 = 127/(10.1*2*pi) = 2 is clearly not enough for
> the approximation to hold so you have to do the exact maths.

Thanks for the correction, Fred.

So you model the circuit as a capacitor in parallel with the inductor and
a series resistor, in which case we have a parallel resonant circuit instead
of a series resonant circuit? Yup, that makes more sense.

The problem can then be solved exactly as follows:

1. First calculate the series resistance R. One equation for the
total impedance of the circuit is [1]

Z_T = (R^2 + X_L^2) / R

You know Z_T and X_L so you can rearrange this equation in the form
of a quadratic equation and solve for R.

2. Now plug this value of R into the relationship

X_C = (R^2 + X_L^2) / X_L

Note that I used my trusty old book [2] from DeVry, which is now
almost 30 years old.

Man, I would've flunked this question myself without doing some
serious review. I've had my head in the digital stuff way too
long.

--Randy

[1] I am using the somewhat arcane TeX typesetting system syntax here
in which a "_" is used for subscript and a "^" is used for a
superscript.

[2] "Introductory Circuit Analysis," Robert L. Boylestad (2nd edition)

--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Randy Yates <randy.yates@sonyericsson.com> writes:
> [...]
> 2. Now plug this value of R into the relationship
>
> X_C = (R^2 + X_L^2) / X_L

X_C = R*Z_T/X_L

would be easier.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

On Sat, 22 May 2004 18:28:23 +0100, "Genome" <Genome@nothere.com> posted this:

>
>"James Meyer" <jmeyer@nowhere.com> wrote in message

>|
>| Perhaps you should switch your career goals over to something like
>| business administration or sales. "Do you want fries with that order,
>Sir?"
>|
>| Jim
>|
>
>Well.... I got it wrong......
>
>By the way the correct question is. "Do you want chips with that?"
>
>DNA
>

I assumed that he'd be too embarrased to stay in the UK.

A sailor was berating a new recruit for using the wrong terminology.
"It's not the floor, it's the deck. And that's not the ceiling, it's the
overhead. The next time I hear you screw something like that up, I'll throw you
through that little round window over there!"

Jim

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

On Sat, 22 May 2004 09:56:33 -0400, John Popelish wrote:

> Steve Hill wrote:
>>
>> Can anyone tell me how I should be calculating Parasitic Inductance,
>> Resistance and Capacitance? Any equations would be helpful. I am
>> revising for a telecommunications module and can't seem to find
>> anything anywhere and with no answers to work with, I am confused
>> whether I am doing it right.
>>
>> Typical question:
>> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
>> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
>
> If an inductance (assumed to be a lumped inductance) looks resistive,
> then it is being resonated (canceled) at that frequency by an equal
> magnitude capacitive impedance. Magnitude of inductive impedance is
> 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> them equal and solve for C.

Impedance? It's reactance. Impedance takes resistance into account.
--
Best Regards,
Mike

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Activ8 wrote:
> On Sat, 22 May 2004 09:56:33 -0400, John Popelish wrote:
>
>> Steve Hill wrote:
>>>
>>> Can anyone tell me how I should be calculating Parasitic Inductance,
>>> Resistance and Capacitance? Any equations would be helpful. I am
>>> revising for a telecommunications module and can't seem to find
>>> anything anywhere and with no answers to work with, I am confused
>>> whether I am doing it right.
>>>
>>> Typical question:
>>> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
>>> resistance is 127ohms. Calculate the parasitic capacitance. [2
>>> Marks]
>>
>> If an inductance (assumed to be a lumped inductance) looks resistive,
>> then it is being resonated (canceled) at that frequency by an equal
>> magnitude capacitive impedance. Magnitude of inductive impedance is
>> 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
>> them equal and solve for C.
>
> Impedance? It's reactance. Impedance takes resistance into account.

So what. Impedance is still correct and so therefore is the statement.
All reactances *are* impedances. I can't even remember the last time I
actually used the word "reactance". Its one of those things that is
introduced in EE 101, but no one really uses in normal electronic
parlance, imo.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

Activ8 wrote:
>
> On Sat, 22 May 2004 09:56:33 -0400, John Popelish wrote:
>
> > Steve Hill wrote:
> >>
> >> Can anyone tell me how I should be calculating Parasitic Inductance,
> >> Resistance and Capacitance? Any equations would be helpful. I am
> >> revising for a telecommunications module and can't seem to find
> >> anything anywhere and with no answers to work with, I am confused
> >> whether I am doing it right.
> >>
> >> Typical question:
> >> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
> >> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
> >
> > If an inductance (assumed to be a lumped inductance) looks resistive,
> > then it is being resonated (canceled) at that frequency by an equal
> > magnitude capacitive impedance. Magnitude of inductive impedance is
> > 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> > them equal and solve for C.
>
> Impedance? It's reactance. Impedance takes resistance into account.

As I understand it, impedance is a complex value. Reactance is the
magnitude of the a purely reactive impedance. So I could have just as
well used the word reactance as magnitude of impedance. But since I
was referring to purely reactive components, I think I am not wrong.
--
John Popelish

Guest · May 23, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

On Sun, 23 May 2004 10:38:05 -0400, John Popelish wrote:

> Activ8 wrote:
>>
>> On Sat, 22 May 2004 09:56:33 -0400, John Popelish wrote:
>>
>>> Steve Hill wrote:
>>>>
>>>> Can anyone tell me how I should be calculating Parasitic Inductance,
>>>> Resistance and Capacitance? Any equations would be helpful. I am
>>>> revising for a telecommunications module and can't seem to find
>>>> anything anywhere and with no answers to work with, I am confused
>>>> whether I am doing it right.
>>>>
>>>> Typical question:
>>>> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
>>>> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
>>>
>>> If an inductance (assumed to be a lumped inductance) looks resistive,
>>> then it is being resonated (canceled) at that frequency by an equal
>>> magnitude capacitive impedance. Magnitude of inductive impedance is
>>> 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
>>> them equal and solve for C.
>>
>> Impedance? It's reactance. Impedance takes resistance into account.
>
> As I understand it, impedance is a complex value. Reactance is the
> magnitude of the a purely reactive impedance. So I could have just as
> well used the word reactance as magnitude of impedance. But since I
> was referring to purely reactive components, I think I am not wrong.

I knew what you meant. Might cause a little confusion for a newbie
though.
--
Best Regards,
Mike

Guest · May 24, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Activ8" <reply2group@ndbbm.net> wrote in message
news:14dbi7r9za74v.dlg@news.individual.net...
> On Sun, 23 May 2004 10:38:05 -0400, John Popelish wrote:
>
> > Activ8 wrote:
> >>
> >> On Sat, 22 May 2004 09:56:33 -0400, John Popelish wrote:
> >>
> >>> Steve Hill wrote:
> >>>>
> >>>> Can anyone tell me how I should be calculating Parasitic Inductance,
> >>>> Resistance and Capacitance? Any equations would be helpful. I am
> >>>> revising for a telecommunications module and can't seem to find
> >>>> anything anywhere and with no answers to work with, I am confused
> >>>> whether I am doing it right.
> >>>>
> >>>> Typical question:
> >>>> A 10.1nH inductor at 1GHz is purely resistive. The measured value of
> >>>> resistance is 127ohms. Calculate the parasitic capacitance. [2 Marks]
> >>>
> >>> If an inductance (assumed to be a lumped inductance) looks resistive,
> >>> then it is being resonated (canceled) at that frequency by an equal
> >>> magnitude capacitive impedance. Magnitude of inductive impedance is
> >>> 2*pi*f*L. Magnitude of capacitive impedance is 1/(2*pi*f*C). Set
> >>> them equal and solve for C.
> >>
> >> Impedance? It's reactance. Impedance takes resistance into account.
> >
> > As I understand it, impedance is a complex value. Reactance is the
> > magnitude of the a purely reactive impedance. So I could have just as
> > well used the word reactance as magnitude of impedance. But since I
> > was referring to purely reactive components, I think I am not wrong.
>
> I knew what you meant. Might cause a little confusion for a newbie
> though.
> --
> Best Regards,
> Mike

zero is a number too, right? 5 + j0 is still complex. as is 0 + j5. but
thats just being pedantic.

Cheers
Terry

Guest · May 27, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"John Popelish" wrote
> Not at all. If the inductor looks purely resistive, it is the
> inductance and capacitance that have canceled each other, leaving
> whatever series resistance the inductor had as the only remaining
> visible impedance. The value of that resistance really isn't involved
> in the calculation of that capacitance. If no inductance remains,
> then XC=XL.

==========================
Resistance values DO affect the effective values of L and C and of the
resonant frequency.

For example, a resistance in series with an inductance can be transformed to
an equivalent higher value parallel resistance and a higher value
inductance. With an associated capacitance this reduces the resonant
frequency.

And a resistance in series with a capacitor can be transformed to a parallel
combination of higher resistance and smaller capacitance which increases
resonant frequency.

The magnitude of the effects increases with lower values of Q = Series R /
X.

Pure values of resistance can be transformed to considerably different
purely resistive values by parasitic L and C.

In the extreme case, at the resonant frequency, effective Rp = L /C / Rs
where Rp and Rs are respectively the parallel and and series resistance
values.

But this is not magic. It's only elementary circuit behaviour.

Parasitic L and C are distributed values. A more exact analysis of the
effects is obtained by considering a lumped resistor to be a short
transmission line. But rarely is this necessary.
----
Reg.

Guest · May 28, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Terry Given" <the_domes@xtra.co.nz> writes:
> [...]
> When I was at University, in a fit of inspired stupidity I analysed a
> 2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
> Unsurprisingly, it was a LOT of work, and gave me the exact same answer as
> the laplace approach.

Damned impressive anyway!
--
% Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven.
%% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and
%%% 919-577-9882 % Verdi's always creepin' from her room."
%%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO
http://home.earthlink.net/~yatescr

Guest · May 28, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Randy Yates" <yates@ieee.org> wrote in message
news:smdl2q5t.fsf@ieee.org...
> "Terry Given" <the_domes@xtra.co.nz> writes:
> > [...]
> > When I was at University, in a fit of inspired stupidity I analysed a
> > 2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
> > Unsurprisingly, it was a LOT of work, and gave me the exact same answer
as
> > the laplace approach.
>
> Damned impressive anyway!
> % Randy Yates % "She's sweet on Wagner-I think she'd die
for

Nah, just handle-cranking. I was hell impressed when my (ex-) father-in-law
showed me a 16x16 matrix he inverted BY HAND (civil engineer). Lots of
cross-checking, and VERY big bits of paper. Now I see why Walter spent
$20,000 on his first HP calculator (alas I cant recall the model no. but it
was bigger than a typewriter)

I also discovered a not-too-dissimilar worked example (Kraus'
electromagnetics IIRC)

It provided an object lesson in the appropriate use of approximations though

Cheers
Terry

Guest · May 29, 2004

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote in message
news:c93sv1$kaj$1@titan.btinternet.com...
>
> "John Popelish" wrote
> > Not at all. If the inductor looks purely resistive, it is the
> > inductance and capacitance that have canceled each other, leaving
> > whatever series resistance the inductor had as the only remaining
> > visible impedance. The value of that resistance really isn't involved
> > in the calculation of that capacitance. If no inductance remains,
> > then XC=XL.
>
> ==========================
> Resistance values DO affect the effective values of L and C and of the
> resonant frequency.
>
> For example, a resistance in series with an inductance can be transformed
to
> an equivalent higher value parallel resistance and a higher value
> inductance. With an associated capacitance this reduces the resonant
> frequency.
>
> And a resistance in series with a capacitor can be transformed to a
parallel
> combination of higher resistance and smaller capacitance which increases
> resonant frequency.
>
> The magnitude of the effects increases with lower values of Q = Series R /
> X.
>
> Pure values of resistance can be transformed to considerably different
> purely resistive values by parasitic L and C.
>
> In the extreme case, at the resonant frequency, effective Rp = L /C / Rs
> where Rp and Rs are respectively the parallel and and series resistance
> values.
>
> But this is not magic. It's only elementary circuit behaviour.
>
> Parasitic L and C are distributed values. A more exact analysis of the
> effects is obtained by considering a lumped resistor to be a short
> transmission line. But rarely is this necessary.
> ----
> Reg.

Thankfully Reg is right. Imagine what a pain most circuit design would be
then. When I was at University, in a fit of inspired stupidity I analysed a
2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
Unsurprisingly, it was a LOT of work, and gave me the exact same answer as
the laplace approach. The problem with approximations is when you dont
realise you are using them

Cheers
Terry

Parasitic values

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