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參數(shù)資料
| 型號： | TEA2028 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | APPLICATION NOTE |
| 中文描述： | 應(yīng)用筆記 |
| 文件頁數(shù)： | 10/47頁 |
| 文件大?。?/td> | 532K |
| 代理商： | TEA2028 |
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V.3.2 - Functional duty of individualblocks
V.3.2.1 - Phase comparator
The duty of this comparator is to issue an output
current proportional to the phase difference be-
tween
φ
IN
and
φ
OUT
.
V.3.2.2 - Low-pass filter
Thisfiltersuppressestheparasiticcomponentcon-
taining the sum of phases, smoothens the phase
difference component and determines the timing
characteristics of the loop.
V.3.2.3 - VCOcentered on 500kHz
This is a voltage-controlledoscillatorwhich gener-
ates an output frequency proportional to the volt-
age applied to its input.
This voltage is delivered by low-passfilter.
V.3.2.4 - Dividerstage
It is used to divide theVCOfrequency(500kHz) by
32 so that it can be compared with the line sync
signal frequencyof 15625Hz.
V.3.3-Functionaldescriptionofbuildingblocks
V.3.3.1 - Phase comparator ”
φ
1”
The comparatoris functionallyequivalent to a sig-
nal multiplier (see Figure 12).
Let’s assume that :
- i
LS
=I sin(
ω
H
t +
φ
IN
) andV
φ
1
= k cos(
ω
H
t +
φ
OUT
)
then :
-
i =i
LS
k
2
(see Figure 13)
- the low-passfilter willsuppressthe 2f
H
frequency
[ sin (
Φ
IN
-
Φ
OUT
) + sin(2
ω
H
t +
Φ
IN
+
Φ
OUT
)]
component
-
φ
IN
-
φ
OUT
differencebeing low :
sin (
φ
IN
-
φ
OUT
)
≈
φ
IN
-
φ
OUT
- the outputcurrentwill bethereforeproportionalto
the phase difference between the signals com-
pared.
In otherwords,theaveragecurrentoverone period
is :
I
AV
T
H
= I
I
AV
= 2I
t
2
π
The comparatorconversion gain is thus :
i
Φ
=I
Later in our discussion we shall consider the two
possiblevalues of the current I.
For the time being, let’s define these values as
follows :
- I = 500
μ
A for ”long time constant” or normal
operation
- I = 1.5mAfor”short time constant” VCR mode or
synchronizationsearch (Mute).
The valuesof Aare therefore :
- A
LONG
= 0.16mA/rd
- A
SHORT
= 0.47mA/rd
Use of comparator inhibition signal is quite useful
under noisy transmission conditions. It eliminates
risk of incorrect comparison during the line scan-
ningphasewhichwouldbeduetothenoisepresent
on LS signal. Horizontal phaseand image stability
are thus highly enhanced.
Characteristics of this inhibition signal will be dis-
cussedat theend of this chapter.
t
S
2
+
t
- I
t
S
2
t
= 2I
t
T
H
and
t =
Φ
T
H
A=
π
(inA/rd)
i
V
+
CC
1.26V
i
LS
I
2I
1mA
500
μ
A
&
LS
Long
1 inhibition
≤
1
Mute
VCR
Video Recognition
VCR Mode
Switching
φ
OUT
1.26V
v
1 Signal
φ
IN
V
φ
I
i
O
LS = 1
T
H
t
S
0
t
I+
I-
2
Figure12
TEA2028 - TEA2029APPLICATIONNOTE
10/46
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