CIRCUIT DESCRI PTION
1 . O u t l i n e o f C i r c u i t
Fig. 1 shows t h e b l o c k d i a g r a m o f t h e c i r c u i t . T h e large
a t t e n u a t i o n ranges use
"T"
or d o u b l e " T " n e t w o r k a n d
t h e small a t t e n u a t i o n ranges use Bridge
"T"
n e t w o r k s .
Each step has 6 0 0 o h m i m p e d a n c e a n d is p r o v i d e d w i t h
capacitors f o r phase c o m p e n s a t i o n .
2 . " T " , D o u b l e
"T"
a n d Bridge " T " N e t w o r k s
T h e " T " n e t w o r k is used in t h e c i r c u i t w h e r e t h e at-
t e n u a t i o n per step is large, w h i l e t h e d o u b l e " T " net-
w o r k is used w h e r e t h e a t t e n u a t i o n per step exceeds 4 0
d B so t h a t t h e e f f e c t o f stray capacitance is m i n i m i z e d
and the accuracy is f u r t h e r i m p r o v e d .
A c c o r d i n g l y , w h e n t h e a t t e n u a t i o n per step is 6 0 d B , t h e
error caused b y a single stage " T " n e t w o r k is ± 6 0 e d B ,
b u t can be reduced t o ± 4 2 £ d B (see N O T E b e l o w ) if it
is d i v i d e d i n t o t w o stages.
N O T E : ± V ( 3 0 £ )
2
+ (30 e )
2
= ± 4 2 e d B ,
w h e r e t h e accuracy o f resistors is ± £ (%).
T h e bridge " T " n e t w o r k is used in t h e c i r c u i t f r o m w h i c h
small a t t e n u a t i o n s are o b t a i n e d . T h e reason f o r t h e use
o f t h i s n e t w o r k is t o reduce t h e n u m b e r o f resistors.
Input
COM
GND
1
Shorting bar
30dB
" T "
network x 2
10dB
" T "
network x 5
1 dB
Bridge " T "
network x 10
Ground plate
Case ground
Fig. 1 B l o c k D i a g r a m
0.1 dB
Bridge " T "
network x 10
Output
COM
4