[SI-LIST] Fwd: Re: impedance and Characteristic impedanece

  Raj,
   
  To add comment to others, the 50 ohm controlled Zo refers to maintaining the 
same cross-section versus length (same line width and distance from return 
path).  The original impedance calculation is usually made using closed-form 
formulas or lossless solvers, or assuming the high freq. limit.  In reality the 
lossy Zo is complex where the real part gets bigger and and the mag. of the 
imaginary part gets bigger at lower freqs.  So for an example lossy high 
freq-limit 50 ohm controlled package line, the complex Zo=79-30i at 10MHz, 
54-6i at 100MHz, and 52-1.5i at 1GHz, and only approaches a mostly real 50.0 
above 5GHz.  Only if this freq-dependent cmplx Zo is considered will you see 
the proper slope on the, eg, "flat parts" of a lossy line TDR simulation.  
However, for a great many board problems, assuming a low-loss or lossless line 
with real Zo=the high freq. limit (or as an alternative, lossless) value is 
practical, so that is what you see done.
   
  N_G.
   
  -----Original Message-----
  From: si-list-bounce@xxxxxxxxxxxxx [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
   
  When I say impedance, it depends on the
  capacitance and inductance. So, these two components depend on frequency = 
(wL and 1/wC, where w=3D 2xpixF).
   
  When I say characteristic impedance, it too has capacitance and inductance 
involved. So when I say I maintain 50 ohm characteristic impedance on my 
board... there may be lot of frequencies involved in the design resulting in 
different characteristic impedance. then how the board is said as a 50 ohm 
impedance controlled..? 
   
  Thanks and regards,  Raj.
    
---------------------------------
  
 
---------------------------------
We won't tell. Get more on shows you hate to love
(and love to hate): Yahoo! TV's Guilty Pleasures list.

------------------------------------------------------------------
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 technical documents are available at:
                http://www.si-list.net

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

Other related posts: