[SI-LIST] Re: impedance and Characteristic impedanece
- From: "Zhenggang Cheng" <zcheng@xxxxxxxxxx>
- To: <arpad.muranyi@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 9 Apr 2007 16:33:43 -0700
Why is it infinte? Any formula ? Why it is not R=3DU/I=3DU/1*U=3D1?
And why this is related to impedance and characteristic impedance?
Sorry for asking so many whys. But I do want to know.
Thanks,
Zheng
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Muranyi, Arpad
Sent: Monday, April 09, 2007 4:14 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: impedance and Characteristic impedanece
Yup! You wouldn't believe how many people
told me that it would be 1 Ohm...
I hope I won't have to explain how this
circuit (and answer) relates to the two kinds
of transmission line impedances...
Arpad
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D20
-----Original Message-----
From: David Banas [mailto:david.banas@xxxxxxxxxx]=3D20
Sent: Monday, April 09, 2007 4:09 PM
To: Muranyi, Arpad; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: impedance and Characteristic impedanece
The impedance is infinite.
-db
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Muranyi, Arpad
> Sent: Monday, April 09, 2007 3:26 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: impedance and Characteristic impedanece
>=3D20
> One of my favorite questions may illustrate the
> impedance question below (or confuse people even
> more)...
>=3D20
> Imagine an ideal voltage-controlled-current-source
> in parallel with a resistor. The resistor has a
> value of 1 Ohm and the output current of the source
> is -1 times the voltage across the parallel combination
> of the current source and resistor. (The negative
> sign is there because I am assuming that the current
> flow is positive when the current goes into the +
> terminal and comes out of the - terminal of the
> source as well as the resistor).
>=3D20
> The HSPICE netlist is:
>=3D20
> R1 node 0 R=3D3D3D1
> G1 node 0 CUR=3D3D3D'-1*V(node,0)'
>=3D20
> What is the impedance of this circuit when you look
> into it (Z11)?
>=3D20
> Arpad
>
=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D=
3D3D=3D3D3D=3D3D3D=3D3D3D=3D3
D=3D
3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D
=3D3D3
> D=3D3D
>
=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D=
3D3D=3D3D3D=3D3D3D=3D3D3D=3D3
D=3D
3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D
=3D3D3
> D=3D3D
> =3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D=3D3D3D
>=3D20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D3D
> On Behalf Of Bill Jones
> Sent: Wednesday, March 21, 2007 3:32 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: impedance and Characteristic impedanece
>=3D20
> Raj,
> =3D3D20
> To add comment to others, the 50 ohm controlled Zo refers to =3D3D
> maintaining the same cross-section versus length (same line width and
=3D3D
> distance from return path). The original impedance calculation is =3D3=
D
> usually made using closed-form formulas or lossless solvers, or
assuming =3D3D
> the high freq. limit. In reality the lossy Zo is complex where the
real =3D3D
> part gets bigger and and the mag. of the imaginary part gets bigger at
=3D3D
> lower freqs. So for an example lossy high freq-limit 50 ohm
controlled =3D3D
> package line, the complex Zo=3D3D3D79-30i at 10MHz, 54-6i at 100MHz, an=
d
=3D
=3D3D
> 52-1.5i at 1GHz, and only approaches a mostly real 50.0 above 5GHz. =3D=
=3D3D
> Only if this freq-dependent cmplx Zo is considered will you see the =3D=
=3D3D
> proper slope on the, eg, "flat parts" of a lossy line TDR simulation.
=3D3D
> However, for a great many board problems, assuming a low-loss or =3D3D
> lossless line with real Zo=3D3D3Dthe high freq. limit (or as an
alternative, =3D3D
> lossless) value is practical, so that is what you see done.
> =3D3D20
> N_G.
> =3D3D20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx =3D3D
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of nagaraj
> Sent: Tuesday, March 20, 2007 9:04 PM
> To: si-list
> Subject: [SI-LIST] impedance and Characteristic impedance
> =3D3D20
> When I say impedance, it depends on the
> capacitance and inductance. So, these two components depend on =3D3D
> frequency =3D3D3D (wL and 1/wC, where w=3D3D3D3D 2xpixF).
> =3D3D20
> When I say characteristic impedance, it too has capacitance and =3D3D=
> inductance involved. So when I say I maintain 50 ohm characteristic =3D=
=3D3D
> impedance on my board... there may be lot of frequencies involved in
the =3D3D
> design resulting in different characteristic impedance. then how the =3D=
=3D3D
> board is said as a 50 ohm impedance controlled..?=3D3D20
> =3D3D20
> Thanks and regards, Raj.
> =3D3D20
> ---------------------------------
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>=3D20
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>=3D20
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