FreeLists / si-list / [SI-LIST] Re: impedance and Characteristic impedanece

["David Banas" <david.banas@xxxxxxxxxx>]

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
>=20
> One of my favorite questions may illustrate the
> impedance question below (or confuse people even
> more)...
>=20
> 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).
>=20
> The HSPICE netlist is:
>=20
> R1  node  0  R=3D3D1
> G1  node  0  CUR=3D3D'-1*V(node,0)'
>=20
> What is the impedance of this circuit when you look
> into it (Z11)?
>=20
> 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
=3D3
> D=3D
>
=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
=3D3
> D=3D
> =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
>=20
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D
> 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
>=20
> Raj,
>   =3D20
>   To add comment to others, the 50 ohm controlled Zo refers to =3D
> maintaining the same cross-section versus length (same line width and
=3D
> distance from return path).  The original impedance calculation is =3D
> usually made using closed-form formulas or lossless solvers, or
assuming =3D
> the high freq. limit.  In reality the lossy Zo is complex where the
real =3D
> part gets bigger and and the mag. of the imaginary part gets bigger at
=3D
> lower freqs.  So for an example lossy high freq-limit 50 ohm
controlled =3D
> package line, the complex Zo=3D3D79-30i at 10MHz, 54-6i at 100MHz, and =
=3D
> 52-1.5i at 1GHz, and only approaches a mostly real 50.0 above 5GHz.  =
=3D
> Only if this freq-dependent cmplx Zo is considered will you see the =
=3D
> proper slope on the, eg, "flat parts" of a lossy line TDR simulation.
=3D
> However, for a great many board problems, assuming a low-loss or =3D
> lossless line with real Zo=3D3Dthe high freq. limit (or as an
alternative, =3D
> lossless) value is practical, so that is what you see done.
>   =3D20
>   N_G.
>   =3D20
>   -----Original Message-----
>   From: si-list-bounce@xxxxxxxxxxxxx =3D
> [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
>   =3D20
>   When I say impedance, it depends on the
>   capacitance and inductance. So, these two components depend on =3D
> frequency =3D3D (wL and 1/wC, where w=3D3D3D 2xpixF).
>   =3D20
>   When I say characteristic impedance, it too has capacitance and =3D
> inductance involved. So when I say I maintain 50 ohm characteristic =
=3D
> impedance on my board... there may be lot of frequencies involved in
the =3D
> design resulting in different characteristic impedance. then how the =
=3D
> board is said as a 50 ohm impedance controlled..?=3D20
>   =3D20
>   Thanks and regards,  Raj.
> =3D20
> ---------------------------------
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