NE545 데이터 시트보기 (PDF) - Unspecified
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NE545 Datasheet PDF : 20 Pages
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S I G N E T I C SD O L B Y - BN O I S EP R O C E S S O TR 5 4 5
N E 5 4 5 BT E S TP R O C E D U R E
EOUIPMENT
1 . L o w d i s t o r t i o n a u d i o g e n e r a t o r( H . P .2 0 4 D )
2 . R M S V o l t m e t e r( H . P .4 0 0 E )
Connect audio generator to the input of the test jig
(Fis. 2al. Adjust the input levelto obtain OdB (580mV)
at pin 3 of the lC. Perform spot frequency measurement
a t t h e o u t p u t ( p i n 7 ) o f t h e l C . A l l r e a d i n g ss h o u l d f a l l
within 12dB with respectto the standardrecordingdata
a s s h o w n i n t h e P r o c e s s o rC h a r a c t e r i s t i c sA n a l y s i s F o r m .
O p t i o n a l l y , r a t h e r t h a n c h e c k i n g a t s p o t f r e q u e n c i e s ,t h e
entire frequency spectrum can be checked using a sweep
generatorand recorder.
INTRODUCTION
The Dolby B-type noise reduction system is designedfor
the reduction of hiss in consumer products. Employing
techniquessimilar to those used in the wideband Dolby
L a b o r a t o r i e sA - t y p e p r o f e s s i o n a ln o i s e r e d u c t i o n e q ui p -
m e n t , t h e B - t y p e s y s t e m r e t a i n st h e a d v a n t a g eo f i n a u d i b l e
a c t i o n ,g o o d m a t c h i n g ,a n d l o w d i s t o r t i o n .
The B-type noise reduction system operates by boosting
l o w - l e v e l h i g h - f r e q u e n c ys i g n a l si n t h e e n c o d e m o d e a n d
attenuatingthe same signalsin a complementary manner
i n t h e d e c o d e m o d e . D u r i n g t h e l a t t e r p r o c e s sn, o i s e i n t h e
treatedfrequency rangeis alsoattenuated.
I n a p p l y i n g n o i s e r e d u c t i o n t o c o n s u m e rt a p e p r o d u c t sa n d
F M r e c e i v e r s ,i t i s n e c e s s a r yt o a p p r e c i a t et h a t t h e f u l l
subjectiveimprovement offered by a 10dB reduction in
hisscan be obtained only if the other performancepara'
meters of the system are of b comparable standard. The
hum level, in particular,must be reducedto a lower value
t h a n i s a c c e o t a b l ew i t h n o r m a l h i s sl e v e l s .
T h e S i g n e t i c s N E 5 4 5 B D o l b y - B N o i s e P r o c e s s o rc a n b e
used in three basic noise reduction circuits - encoders,
d e c o d e r s ,a n d s w i t c h a b l e p r o c e s s o r sw h i c h w i l l o p e r a t e i n
either mode.
C I R C U I TO P E R A T I O N
The operation of the noise reduction system will be
describedwith referenceto Figure 25, which is a block
diagramof the encodeand decode processor.
Referring to Figure 25, signals enter the encoder via
a m p l i fi e r A a n d p a s st o a l o w - p a s sf i l t e r J w h i c h a t t e n u a t e s
a l l u n w a n t e d f r e q u e n c i e s .s u c h a s t a p e r e c o r d e rb i a so r F M
m u l t i p l e x s i g n a l s ,t o a l e v e l o f l e s s t h a n 4 5 d 8 . l f s u c h
s p u r i o u ss i g n a l sa r e a b o v e t h e t h r e s h o l d o f t h e c o m p r e s s o r ,
t h e f u l l 1 0 d B o f l o w l e v e l p r e - e m p h a s i sw i l l n o t b e
obtained.
The signalat the output of amplifier B is split into two
p a t h s ,o n e , k n o w n a s t h e m a i n p a t h , p r o v i d e sa n u n a l t e r e d
signal component d irectly to the output via adder E,
while the other, known as the side chain, controls the
d y n a m i c c h a r a c t e r i s t i cosf t h e p r o c e s s o r .
T h e s i d ec h a i nc o n t a i n sa h i g h - p a s sd y n a m i c f i l t e r c o m p r i s i n g
c a p a c i t o r sC 3 0 1 , C 3 0 2 , C 3 0 3 a n d r e s i s t o r sR 3 0 i , R 3 0 2 a n d
t h e c o n t r o l l e d r e s i s t a n c eF . A t l o w s i g n a l l e v e l sF h a s a
high valueand the first part of the filter (i.e.C301, C302,
a n d R 3 0 1 ) t h e n c o n t r o l s t h e r e s p o n s eo f t h e s i d e c h a i n .
The output of the filter isamplifiedby amplifierC and the
r e s u l t i n gn o i s e r e d u c t i o n s i g n a li s a d d e d t o t h e m a i n s i g n a l
i n a d d e r E . T h e l o w - l e v e lg a i n o f t h e s i d e - c h a i ni s s u c h t h a t
t h e o v e r a l lo u t p u t i s i n c r e a s e db y i 0 d B a t 5 k H z w h e n t h e
n o i s er e d u c t i o n s i g n a li s a d d e d .
F I G U R E2 5
E N C O D E - D E C O DBEL O C KD I A G R A M
R302
c 301
N O T E :A L L R E S I S T O RS T A N D A R DA N D A R E I V I E A S U R ElDN O H M S
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