Here is something that I wrote for one of our internal 
        newsletters a while ago:
        
        "Technically speaking, "impedance" is the total opposition to 
        alternating current (AC) flow by a circuit.  Impedance is 
        measured in "ohms", just like resistors (typical values are at 
        about 50 - 75 ohms).  It becomes important in high speed 
        electronic equipment when the signals of various components of a 
        circuit must be synchronized.  The circuits in the equipment can 
        slow down the signals, relative to other circuit devices, unless 
        synchronization is done by controlling the impedance.  Design 
        engineers therefore choose a critical region (or regions) of the 
        circuit to have a controlled impedance range which the 
        manufacturer must meet.  This brings the printed circuit board 
        into a more active role, instead of the passive role it has had 
        as a mounting board and connector for the components."
        
        
        I hope it helps.
        
        Matt Byrne
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______________________________ Reply Separator _________________________________
Subject: Controlled Impedance
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    7/7/95 12:31 PM


Does anyone out there have a simple, non-technical definition 
of controlled impedance? We are having some difficulty 
explaining satisfactorily to some management types.
        
Thanks,
Bob Smith 
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