That's just what I was thinking. The microstrip model is pretty unreliable
for that impedance but
a diff pair sounds a little better. I can hit 333 ohms with a 5mil trace,
1.2oz finished, 72mil gap and 59mil height above GND plane using PTFE 2.1.
Just one way to do it...could use a 4 mil trace if possible as well.
Ken
------------------------------
Kenneth J. Wood
Saturn PCB Design
www.saturnpcb.com
----- Original Message -----
From: "Brooks,Bill" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, April 15, 2005 5:41 PM
Subject: Re: [TN] impedance value very high
> Just a guess... but the old TV antenna 'twin lead' was 300 ohm
> impedance...
> maybe they want a differential impedance between two lines on the board
> rather than an impedance with respect to a ground plane like micro strip
> does ???
>
> Bill Brooks - KG6VVP
> PCB Design Engineer , C.I.D.+, C.I.I.
> Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
> e-mail:[log in to unmask]
> http://www.dtwc.com
> http://pcbwizards.com
>
> -----Original Message-----
> From: Mcmaster, Michael [mailto:[log in to unmask]]
> Sent: Friday, April 15, 2005 2:37 PM
> To: [log in to unmask]
> Subject: Re: [TN] impedance value very high
>
> I ran this through our field solver. For a 1 mil trace, you'd need a
> dielectric thickness of about 5 inches to do this.
>
> Thick as a brick.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Bonatti
> Sent: Friday, April 15, 2005 10:28 AM
> To: [log in to unmask]
> Subject: [TN] impedance value very high
>
> I have a puzzling question for you impedance experts:
>
> A customer is asking for a PCB characteristic impedance for a single
> trace to be 332 Ohms +/- 5%.
>
> I've never seen a requirement for an impedance to be this high. Has
> anyone here seen this before? HyperLynx is choking on this.
>
> Thank you in advance for your input, it is greatly appreciated.
>
>
> Eric Bonatti, C.I.D.
> PCB Designer
> StrataFLEX Corporation
> Tel.: +1.416.752.2224 xt.227
> Fax: +1.416.752.6719
> Toll Free: +1.866.771.7765
> E-mail: [log in to unmask]
> Web: www.strataflex.com
>
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