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參數(shù)資料
| 型號(hào)： | 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)： | 16/47頁 |
| 文件大?。?/td> | 532K |
| 代理商： | TEA2028 |
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It is therefore deduced that the systemcan follow
all input phase variations without producing any
staticerror.
In practice, there will be a slight error due to the
input bias current ”I
B
” of VCO, which is 0.55
μ
Aat
f
O
= 500kHz. This DC current is delivered by a
phase comparator which will generate a phase
error of :
- long time constant :
I
B
A
LONG
= 0.55
10
3
= 3.4
10
-3
rd or 35nsin
t
Φ
LONG
=
0.16
- short time constant :
Φ
SHORT
=
I
B
A
SHORT
= 12ns
These two errors cause a horizontal picture dis-
placement. On a large screen of 54cm wide, this
will be : 64 - 12 = 52
μ
s, which for both modes
corresponds to a shiftof :
LINE
=
Φ
LONG
Φ
SHORT
52
It is obvious that such displacement can be fully
neglected.
520 = 0.24mm
Response to a FrequencyStep
- The inputphase is :
Φ
IN
(t) =
ω
t
whichas a functionof (p) is :
Φ
IN
(p) =
ω
p
2
- The accuracyis :
(
Φ
IN
Φ
OUT
) =
lim
lim
p
>
0
where R = 500k
at f(o)
In thiscase, the phaseerror depends on both, the
magnitudeof thefrequencystep andthe staticgain
ABR.
In general,
f
fwhich is the open-loopstaticgain, is
taken into consideration.
ω
Φ
= ABR =
f
T
H
(B’in kHz/V)
- In normalmode : A
LONG
= 0.16 mA/rd
f
t= 5.5kHz/
μ
s, R = 500k
p
>
0
ω
p
+
ABf
(
o
)=
ω
ABR
2
π
f
t
×
2
π
= A
2
π
B’
R
t= AB’R
2
π
- In VCR mode : A
SHORT
= 0.47 mA/rd
f
t= 16.5kHz/
μ
s
Note : The capture range is specified within
±
500Hz withrespect to15625Hz.
NumericalExample
Let’s suppose that in VCR mode there is a fre-
quencyvariation of
±
100Hz,thiswill yield aphase
variation of 0.1/16.5, i.e.
±
6ns which, on a 54cm
wide screen, will produce a horizontal shift of
LINE
=
±
0.06mm !
It isobviousthatan excellentimagestabilityisthus
obtained.
V.3.6.2- Dynamic study
The loop response in transient mode is quite im-
portant. It determines the overall system stability
and the phase recovery time, which are imposed
by the external filter ”f(p)”.
The close-loop transfer function is equivalentto a
secondorder system. These time constants are in
practice displayed on screen by abar deliveredby
a specialpatterngeneratorrepresentingthephase
errors.
The following optimizedresults wereobtainedfrom
filter f(p) connectedto Pin22.
Filter component values are :
R1 = 4.7k
, C1 = 2.2
μ
F, C = 10nF
A. LONGTIME CONSTANT
- At
t of 4
μ
s
N=18 lines, i.e.
τ
LONG
= 1.15ms.
System oscillations are perfectlydamped.Image
stabilitywith anoisy video signal is very satisfac-
tory.
B. SHORT TIME CONSTANT
- At
t =4
μ
s
N = 5 lines,i.e.
τ
SHORT
= 0.32ms
- n = 5 lines
One should notice fast phase recovery, naturally
followed by bounced oscillations due to the char-
acteristics of a secondorder device.
As given in applicationdiagram section 6, an other
alternative would be to use the following compo-
nent values: R1= 3.9k
, C1 = 4.7
μ
F, C = 15nF.
TEA2028 - TEA2029APPLICATIONNOTE
16/46
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