ESI VideoBridge 2150, Service Manual

Page: 180 / 332

T h e d i f f e r e n t i a l a m p l i f i e r c o n s i s t s of 3 s e c t i o n s o f q u a d - a m p l i f i e r
U 1 3 .
I t s i n pu t i s s e q u e n t i a l l y s e l e c ted by t h e i np u t m u l t i p l e x e r UI O .
T h e mu l i t p l e x e r s e l e c ts e i t h e r t h e vol t a g e d r op a c r o s s t h e u n k n own ,
t h e v o l ta g e d rop a c r o s s t h e s ta n da rd ( r a ng e ) r e s i s t o r , o r t he 1 . OV RMS
r e fe r e n c e vol t a g e f o r me a su re me n t . T h e re f e r e n c e vo l ta g e i s me a s u r e d
f i r s t . The m e a s u r e d re f e r e n c e vol t a g e i s r e c o r d e d a s a re f e r e n ce
n u m be r o f cou n t s ( A/ D c o n v e r t e r co u n t s ) a ga i n s t w h i c h t h e me a s ured
u n k n own a n d s ta nda r d s i g na l s a r e c ompa r e d .
3 . 3 . 2 . 6 V a r i a b l e Ga i n
F rom Rang e Ga i n A m p l T
T Ph
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ec I l er
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T P5
1 6 1 5
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6 5 4 :3
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F i gure 3 - 1 0 . Va r i a b l e Ga i n Ampl i f i e r
The va r i a b l e ga i n a m p l i f i e r ( V GA ) , U 1 7 , w o r k s i n c on j u n c t i on w i t h t h e
l e v e l s e t a n d t h e r a n g e g a i n t o b o o s t t h e m e a s u r e d s i g n a l t o t h e
pr ope r ope ra t i ng l e ve l s f o r t he pha s e re c t i f i e r . The VGA i s a pro­
g ra m ma b l e DAC capa b l e of p r o d u c i n g s i g na l ga i n s of 1 to 2 5 6 .
3
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1 6
e / s / i 2 1 5 0/ 2 1 6 0 5 /8 5