[SI-LIST] Re: capacitor impedance in time domain
- From: Steve Weir <weirsi@xxxxxxxxxx>
- To: arpad.muranyi@xxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Jan 2005 14:37:26 -0800
Arpad, this would be a good time to use Jon Powell's si-draw tool. But let
me try this without:
driver => txline => coupling cap => txline => terminator
Now, let's suppose the driver has a Tr of 100ps, a Tf of 100ps, and a pulse
width of 2.4ns, an output impedance of 0.0001 ohms, and a drive level of
2.5V. Let's try three different values of coupling capacitors, all in the
same 0402 body and 50 ohm txlines.
10pF
1nF
100nF
Now, what sort of wave form do you expect to see at each point?
I know what my answers are: 10pF lots of reflection towards the source and
droop towards the terminator. 1nF and 100nF very little reflection or
droop. Plug it into your favorite simulator and see what you get.
Regards,
Steve
At 02:03 PM 1/28/2005 -0800, Muranyi, Arpad wrote:
>You will get full reflection, because the impedance
>you need to use for the equation you quoted is the
>small signal (AC) impedance. Referring to my previous
>posting a short time ago, the constant current source
>equivalent during the ramping portion of your trapezoid
>waveform has a (finite dV) / (dI =3D 0) =3D> infinite impedance.
>
>The question I have for you is this: where do you mean
>that your waveform is trapezoid? At the beginning of
>the T-line, or at the end, where the capacitor is?
>If the first, be prepared for a non trapezoid waveform
>at the capacitor, because the T-line and the cap forms
>an RC circuit, who's response is an exponential waveform.
>If the ramp is faster the RC constant you will see
>an exponential waveform, if it is slower, you will see
>a more or less trapezoid waveform.
>
>I hope this helps,
>
>Arpad
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On Behalf Of group_delay
>Sent: Friday, January 28, 2005 1:48 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: capacitor impedance in time domain
>
>
>hi all,
>what i really want to do is find out how much waveform gets reflected
>from the end of a lossless transmission line terminated with a
>lossless capacitor, assuming the input waveform is a trapezoidal
>signal. I know this can be computed using: gamma =3D (Zl-Zo)/(Zl+Zo),
>but this requires you to calculate Zl for the time domain signal. If I
>wanted to avoid it and use time domain analysis, how would I setup the
>equation?
>
>thanks,
>chris
>
>
>--- In si-list@xxxxxxxxxxxxxxx, steve weir <weirsp@xxxx> wrote:
> > matthias, in the time domain we would solve the differential
>equations for=20
> > the network, or more likely using a computer program we would solve =
>the=20
> > difference equations over a series of discrete time steps. Now in
>either=20
> > case we could express impedance as dv/dt / di/dt. But I don't know =
>how=20
> > useful it would be towards either visualizing behavior, or solving the =
>
> > equations. Let's take the trapezoidal wave for instance. An =
>effective=20
> > impedance is pretty easy to come by on each: the rising, and falling=20
> > portions of the waveform from the capacitance expression C =3D
>i/dv/dt, Z =3D=20
> > dv/dt / di/dt =3D 1/(dv/dt * C ). The flat portions are troublesome
>as are=20
> > the vertices, since dv/dt theoretically goes to zero and the
>impedance from=20
> > the formula jumps to an infinite value. Intuition should tell us
>that this=20
> > is wrong, as
>
> coupling capacitors routinely pass high frequency pulses.
> >=20
> > In the frequency domain, we have this nailed. We don't have=20
> > discontinuities at the vertices. The vertices and flat portions =
>follow=20
> > curves formed by the frequency components, and rather than a flat
>section=20
> > containing DC and no HF, quite the opposite is true: the flatter we
>want=20
> > the pulse tops to be, the higher the frequency content required. This =
>
> > aligns with our intuition. But when we transform the representation
>back=20
> > to the time domain, those piecewise linear segments are now curved
>solving=20
> > the discontinuities at the vertices and eliminating the flat slopes
>with=20
> > theoretically infinite Z between the edges.
> >=20
> > So if someone wanted to look only at the rising and falling edges, an=20
> > impedance in the time domain is reasonable, and possibly even
>useful. But=20
> > it really gets awkward when dealing with the whole waveform unless
>we first=20
> > perform frequency limiting operations, most easily performed in the=20
> > frequency domain.
> >=20
> > I am not an expert on algorithms, so I really can't say from an error=20
> > analysis and computational efficiency standpoint what is really the
>best=20
> > way to perform a transient analysis. But in my naivete, I would be=20
> > inclined to transform everything into the frequency domain, compute =
>the=20
> > solution and transform back. In my feeble mind, this would avoid
>some of=20
> > the discontinuity and convergence problems in SPICE and more closely=20
> > follows nature. But since people a whole lot better at math than I
>have=20
> > worked long and hard on those algorithms, I suspect either the=20
> > computational overhead, or error build-up of my naive approach would =
>be=20
> > unacceptably high. Maybe what this world needs is a five cent, 256 =
>bit=20
> > floating point, matrix solver!
> >=20
> > Steve.
> >=20
> > At 10:13 PM 1/26/2005 +0100, Matthias Bergmann wrote:
> > >
> > >Hello, I don`t understand why impedance should be limited to =
>Frequency
> > >domain. What impedance are we speaking about ? For example the
> > >characteristicimpedance Z of a transmission line also exists in
>time domain.
> > >If you look along a transmission line, v(t) / i(t) have got
>singularities
> > >(undefined, infinite), these are called short and open ?!?!?
>Furthermore
> > >mostof the simulation programs use the time domain because it permits
> > >non-linearities. I don`t know how what happens when your impulse is
> > >trapezoidal, but if it was a rectangular and your load is a
>capacitance, you
> > >are answer would look like an exponential function, with your
>reflection
> > >co-efficient as initial value. Regards, Matthias Bergmann P.S.:
>Yes, use
> > >SPICE or ADS ! _m |---------+---------------------------------->
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >-list@xxxx>          
> > >-LIST] Re: capacitor impedance in time
> >
> >domain          &#=
>160;
> >
> >60I           =
>60;
> > >          |
> >
> > >-----------------------------------------------------------------=
>----
> > >--  -----------------------------------------| >I could be
>wrong >but
> > >tome >impedance is a concept strongly related to Frequency domain.
> >>It is
> > >meaningful just in that domain. Absolutely. If you define impedance =
>as
> > >voltage/current, then you run into great difficulties if you try to
>do it in
> > >the time domain.  In general, with any complex impedance,
>v(t)/i(t) has
> > >singularities (undefined, infinite). I consider impedance =3D
>v(s)/i(s) or
> > >v(f)/i(f), which makes it a strictly frequency domain parameter.
>Regards,
> > >Andy
>------------------------------------------------------------------ To
> > >unsubscribe from si-list: si-list-request@xxxx with 'unsubscribe'
> > >inthe Subject field or to administer your membership from a web
>page, go to:
> > >http://www.freelists.org/webpage/si-list For help:
> > >si-list-request@xxxx with 'help' in the Subject field List FAQ wiki
> > >page is located at:
> >
> >            &=
>#160;
> > >  http://si-list.org/wiki/wiki.pl?Si-List_FAQ List =
>technical
> > >documents are available at:
> >
> >           =
>60;
> > > http://www.si-list.org List archives are viewable at:
> >
> >            =
> 
> >
> >           http:/=
>/www.
> > >freelists.org/archives/si-list or at our remote archives:
> >
> >           =
>60;
> >
> >          http://group=
>s.yah
> > >oo.com/group/si-list/messages Old (prior to June 6, 2001) list
>archives are
> > >viewable at:
> >
> >            =
> 
> >
> >           http:/=
>/www.
> > >qsl.net/wb6tpu
> > >------------------------------------------------------------------
> > >To unsubscribe from si-list:
> > >si-list-request@xxxx with 'unsubscribe' in the Subject field
> > >
> > >or to administer your membership from a web page, go to:
> > >http://www.freelists.org/webpage/si-list
> > >
> > >For help:
> > >si-list-request@xxxx with 'help' in the Subject field
> > >
> > >List FAQ wiki page is located at:
> > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> > >
> > >List technical documents are available at:
> > > http://www.si-list.org
> > >
> > >List archives are viewable at:
> > > http://www.freelists.org/archives/si-list
> > >or at our remote archives:
> > > http://groups.yahoo.com/group/si-list/messages
> > >Old (prior to June 6, 2001) list archives are viewable at:
> > > http://www.qsl.net/wb6tpu
> > >
> >=20
> >=20
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxx with 'unsubscribe' in the Subject field
> >=20
> > or to administer your membership from a web page, go to:
> > http://www.freelists.org/webpage/si-list
> >=20
> > For help:
> > si-list-request@xxxx with 'help' in the Subject field
> >=20
> > List FAQ wiki page is located at:
> > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> >=20
> > List technical documents are available at:
> > http://www.si-list.org
> >=20
> > List archives are viewable at: =20
> > http://www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
>
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>http://www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
>List technical documents are available at:
> http://www.si-list.org
>
>List archives are viewable at: =20
> http://www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
> =20
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>http://www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
>List technical documents are available at:
> http://www.si-list.org
>
>List archives are viewable at:
> http://www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
The weirsp@xxxxxxxxxx e-mail address will terminate March 31, 2005.
Please update your address book with weirsi@xxxxxxxxxx
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
- Follow-Ups:
- [SI-LIST] Re: capacitor impedance in time domain
- From: Alan Hilton-Nickel
Other related posts:
- » [SI-LIST] capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- » [SI-LIST] Re: capacitor impedance in time domain
- [SI-LIST] Re: capacitor impedance in time domain
- From: Alan Hilton-Nickel