TEA2029 Ver la hoja de datos (PDF) - STMicroelectronics
Número de pieza
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Fabricante
TEA2029 Datasheet PDF : 47 Pages
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TEA2028 - TEA2029 APPLICATION NOTE
Figure 13
i LS
I
tS
0
t
ϕe
vϕ1
+1
0
t
-1 ϕOUT
i
I+
t
I-
V.3.3.2 - Low-pass filter (see Figure 14)
Its main function is to reject the 2fH (31kHz) fre-
quency component delivered by the phase compa-
rator.
It also defines the characteristics of the loop in
transient mode.
The filter is built around two sub-sections which
determine the stability and the response time of the
loop in the following modes of transmission :
Normal or VCR modes. See section V.3.6 ”Dy-
namic study of φ1”.
Figure 14
5.6V
VCO
Stage
R1
4 .7kΩ
C1
2.2µF
C
10nF
22
i
V
ϕ1
Comparator
i
R1
C
C1
VCO
RV
R is the dynamic input resistance of the VCO.
The filter transfer function may be defined as fol-
lows :
-
f(p)
=
V
i
= Z(p)
-
Z(p) =
R
1
+
p
(R
C
+
1 + R1 C1 p
R1 C1 + R C1) +
R R1
C C1
p2
The second order terms of the denominator can be
converted to first order products as a function of
frequency as follow :
f(jf)
=
R
1
+
j
1+
f
f2
j
f
f1
1
+
j
f
f3
with R1 = 4.7kΩ, R = 500kΩ, C1 = 2.2µF, C = 10nF
we obtain :
-
f1
=
2π
1
R1
C1
=
15.4Hz
-
f2
=
2π
(R
C1
+
1
R
C
+
R1
C1)
=
0.14Hz
- f3 = 3.43kHz
Figure 15
20 log |f|
20 log R
0
Arg (z)
f2
f1
f3
0.14Hz 15.4Hz 3.43kHz
0
π
2
(log scale)
f
f
V.3.3.3 - VCO (Voltage Controlled Oscillator)
Its function is to generate a frequency proportional
to a control voltage issued externally, by the low-
pass filter in our case.
The period of the output signal is used as timing
reference for various functions such as, horizontal
and vertical time bases. The frequency range must
be short and accurate :
- It must be short since the power dissipated within
the horizontal scanning block is inversely propor-
tional to the line frequency.
- The accuracy is required if the adjustment is to
be omitted.
The basic arrangement is to employ a ceramic
resonator (or ceramic filter) which has quite stable
characteristics as a function of frequency.
A filter whose resonating frequency is a multiple of
line frequency (15625Hz) is to be selected. An
example is 32 ⋅ 15625 = 500kHz.
A. 503kHz CERAMIC FILTER
Figure 16
Figure 17
Symbol
Equivalent Circuit
R1
L1 C1
C0
11/46
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