Kenwood DP-1100 B Service Manual page 4

1 FUNDAMENTALS
1-1 S A M P L I N G
A n a n a l o g v o l t a g e is c o n t i n u o u s in respect t o t i m e , a n d has a
value at e a c h t i m e of t t , t , etc. as s h o w n in Fig. 1.1 a n d as
1 ( 2 3
w e l l a value at any t i m e b e t w e e n t
Voltage
Fig.
If an a n a l o g v o l t a g e is represented c o r r e s p o n d i n g t o a c o d e
s y s t e m , t h e a n a l o g voltage over the definite t i m e range of t
t is m a d e of the indefinite n u m b e r of c o d e s . In order t o
2
t r a n s m i t a digital signal c o r r e s p o n d i n g t o t h e voltage at t
needs a definite t i m e l e n g t h , b u t w h e n t r a n s m i t t i n g indefinite
c o d e s , t h e t r a n s m i s s i o n d o e s n o t e n d forever.
Voltage
Fig. 1.2
T h e r e f o r e , in case w h e r e an a n a l o g v o l t a g e is c o n v e r t e d t o a
c o d e d s y s t e m , a n a l o g v o l t a g e s at t i m i n g s w i t h s o m e interval
are o n l y c o n v e r t e d as s h o w n in Fig. 1.2. W i t h s u c h a p r o ­
c e s s , t h e definite n u m b e r of c o d e s c o r r e s p o n d i n g t o the
definite t i m i n g s , f o r e x a m p l e , five c o d e s f o r t h e t i m e interval t
t o t are p r o d u c e d .
5
W h e n h a v i n g t r a n s m i t t e d c o d e s d e s c r i b e d in Fig. 1.2, o n l y
five c o d e s c a n be received at the receive side b e t w e e n t
t . T h e n u m b e r of v o l t a g e values r e p r o d u c e d t h e r e b y is only
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f i v e , a n y v o l t a g e at t i m i n g s e x c e p t t
d e t e r m i n e d .
H o w e v e r , if the f r e q u e n c y c o m p o n e n t ( 2 0 kHz) of the original
a n a l o g signal is less t h a n the value ( 4 4 . 1 kHz) d e p e n d i n g
u p o n t h e t i m e interval b e t w e e n t i m i n g s t
c o d i n g is s t a g e d , e v e n t h e value for n o n - t r a n s m i t t e d p o r t i o n s
c a n be r e p r o d u c e d . T o pick u p a n a l o g values at a fixed t i m e
interval by s u c h a process is called " s a m p l i n g " .
II. FUNDAMENTALS
a n d t .
x 2
Time
1.1
t o
t
it
1 (
t Time
5
t
a n d
t
t , t , etc. c a n n o t be
1 ( 2 3
t , t , etc. at w h i c h
1 ( 2 3
1-2 Q U A N T I Z A T I O N
Fig. 1.3 i n d i c a t e s o n e e x a m p l e w h e r e a n a l o g signals r a n g i n g
f r o m O V t o 1 0 V are c o n v e r t e d t o 1 1 - s t e p v o l t a g e values of
0 V , 1 V , 2 V 9 V a n d 1 0 V via r o u n d - o f f . W i t h t h i s c o n v e r ­
s i o n , p r e p a r a t i o n of o n l y 11 kinds of c o d e s is n e e d e d . T o c o n ­
vert an a n a l o g signal t o a kind of a digital signal w i t h t h e p r o ­
cess of r o u n d - o f f or t h e like is called " Q u a n t i z a t i o n " .
Voltage (V)
Fig. 1 . 3
Amplitude
Fig. 1.4
D P - 1 1 0 0 B II
Digital Voltage Converted by
Rounded-Off
Analog Voltage
Time
Sampling
Quantization