advantest corporation TR5821, Руководство по эксплуатации

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T h e le a s t s ig n if ic a n t d ig it o n t h e r e a d o u t. C o u n tin g r e s o lu tio n d iff e rs w ith
g a te tim e . A t a g a te tim e o f 1 s e c o n d , t h e r e s o lu tio n is 1 H z w ith a ty p ic a l
c o u n te r .
D ire c t C o u n tin g
T h e d ire c t c o u n tin g is th e m o s t f u n d a m e n ta l m e t h o d t o m e a s u re th e f r e q u e n ­
c y . (S e e th e fig u re b e lo w .) T h is s c h e m e is w id e ly u s e d fr o m t h e a u d io fr e ­
q u e n c y b a n d t o th e U H F b a n d . In t h e d ir e c t c o u n tin g m e t h o d , th e u p p e r
lim it o f fr e q u e n c y m e a s u r e m e n t is d e te r m in e d b y th e g a te tim e a n d th e
f r e q u e n c y r e s o lu tio n . E n h a n c e m e n t o f t h e p e r f o r m a n c e o f th e s e m ic o n d u c ­
t o r d e v ic e s a n d a d v a n c e d c ir c u it b o a r d te c h n o lo g y h a v e re a liz e d a c o u n t e r o f
1 G H z u tiliz in g th e d ir e c t c o u n t in g te c h n iq u e s .
Counting Resolution
E x p a n d in g R e c ip ro c a l M e th o d
T h e m e t h o d u s e d b y e le c tr o n ic c o u n t e r s t o m e a s u re a p e r io d , e x e c u te in v e rse
c a lc u la tio n (1 /p e r io d ) , a n d d is p la y th e f r e q u e n c y is c a lle d th e re c ip ro c a l
m e t h o d .
T h e m a in f e a tu r e o f th is m e t h o d is t h a t , in p e r io d m e a s u r e m e n t, it e n a b le s
f r e q u e n c y m e a s u r e m e n t o f h ig h - r e s o lu tio n a n d h ig h -p re c is io n u p t o th e o r d e r
o f th e in te r n a l tim e b a s e . F o r e x a m p le , le t th e tim e b a s e b e 1 0 0 x 1 0 ‘9 s , th e n
7 -d ig it d is p la y is a lw a y s p o s s ib le w h e n a f r e q u e n c y ( 1 0 M H z o r le ss) is m e a ­
s u re d a t a g a te tim e o f 1 s e c o n d . T o o b ta in a 1 0 -d ig it d is p la y a t a g a te tim e o f
1 s e c o n d w ith th is m e t h o d , th e i n te r n a l tim e b a s e m u s t b e 1 0 0 x 1 0 ’12s
(e q u iv a le n t t o 10 G H z ). T o re a liz e a 1 0 G H z tim e b a s e , th e tim e e x p a n d e r
m e t h o d is u s e d t o g e t h e r w ith t h e re c ip ro c a l m e t h o d , t h u s e n a b lin g a h ig h -
re s o lu tio n h ig h - p re c is io n f r e q u e n c y m e a s u r e m e n t. T h is m e t h o d is c a lle d th e
e x p a n d in g re c ip ro c a l m e t h o d . ( * S ee T im e E x p a n d e r M e th o d .)
G a te T im e
T h e tim e d u rin g w h ic h a c o u n t e r m e a s u re s t h e i n p u t sig n a l. D u rin g th is tim e ,
th e G A T E la m p u s u a lly g o e s o n t o n o t i f y th e u s e r t h a t th e i n p u t sig n a l is
b e in g m e a s u re d .
Gate
M easurem ent in p u t o-
T im e base o-
A — 5