Hi Scott,

Characteristic impedance describes the impedance of a trace on a printed
circuit which can be either a microstrip (surface or embedded trace over
a single ground plane) or stripline (symmetrical or off-set trace
between two ground planes).

My understanding is that differential impedance describes two parallel
traces where in addition to actual ground planes in the printed circuit
construction, there is an imaginary ground plane created between them
where there is effectively 0 volts. The impedance of the pair of traces
must be measured simultaneously to give the differential impedance
value. This is a more complex system to characterise.

Polar Instruments at www.polar.co.uk have done much work on this and
have a test machine which will measure differential as well as single
trace impedance. They have also developed an impedance calculator that
covers differential impedance which they sell separately.

Best regards

>Could I please get some feedback as to the definitions and difference between
>characteristic versus differential impedance?  I have customers that ask for
>both but can't explain what they are actually looking for.  Any help would be
>appreciated.
>Thanks,
>Scott
Paul Gould
[log in to unmask]
Teknacron Circuits Ltd
Fax: 1983 865141
Tel: 1983 866531

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################