I've been looking into controlled impedance at various times over the 
past several months.  John, could your customer have designs calling for 
differential impedance measurements? 

Sources of information on controlled impedance, that I have used include 
Hewlett Packard Application Notes 62, 62-2, and 62-3.  They deal with TDR 
applications.  A helpful engineer at HP in Loveland, CO, had them sent to 
me.  Alson Wong is his name;  phone is 800-452-4844.  

The TechNet had references to test equipment made by Polar INstruments.  
Polar equipment seems oriented to production testing of controlled 
impedance panels, but it less expensive than TDR and may be easier to 
use.  Polar's US number is 800-328-0817.

Just yesterday I tried to order IPC-2141, the title of which is, 
approximately, "Design Guidelines for Controlled IMpedance".  It was just 
published, so I presume few people have studied it.  I expect it will be 
helpful.  Cost to IPC members is 25$.

Finally, on another subject, for anyone who has read this far, my thanks 
to all who responded to my question about ink on surface mount pads.

Lou Hart


.

On Wed, 29 May 1996, John Parsons wrote:

> This controlled impedance stuff is new to us...
> 
> All the reading I have done seems to imply that reference planes are adjacent to the signal plane.  Is this typically the case, or always the case?
> I have a customer who keeps submitting designs which call for a controlled impedance line where the reference plane is not adjacent.
> 
> Any input in helping us understand this would be appreciated.
> 
> Regards
>