Shield Grounds on Shielded Twisted Pair Single Point Ground Circuits

Abstract

T h i s p a p e r d i s c u s s e s t h e e f f e c t o f im pr ope r s h i e l d grou n d s on s h i e l d e d t w i s t e d p a i r w i r i n g when t h a t w i r ­ in g i s used in a s i n g l e p o i n t c i r c u i t ground c o n f i g u r a ­ t i o n . Low f r e q u e n c y m a g n e t i c f i e l d c o u p l i n g t o t h a t w i r e c i r c u i t c a n c a u s e a v o l t a g e g r a d i e n t t o e x i s t b e ­ tween t h e w i r e and t h e s h i e l d . T h i s r e s u l t s i n a p o r ­ t i o n o f t h e unwanted n o i s e v o l t a g e b e i n g p r e s e n t w i r e t o w i r e . The a c t u a l w i r e c o u p l i n g mechanism i s shown a l o n g w i t h t h e e q u i v a l e n t c i r c u i t s and t h e p a r a m e te r s need ed t o c a l c u l a t e t h e e f f e c t and make a good EMC j u d g ­ ment.