TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 10

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TEA2028 - TEA2029 APPLICATION NOTE
V.3.2 - Functional duty of individual blocks
V.3.2.1 - Phase comparator
The duty of this comparator is to issue an output
current proportional to the phase difference be-
tween
V.3.2.2 - Low-pass filter
This filter suppresses the parasitic component con-
taining the sum of phases, smoothens the phase
difference component and determines the timing
characteristics of the loop.
V.3.2.3 - VCO centered on 500kHz
This is a voltage-controlled oscillator which gener-
ates an output frequency proportional to the volt-
age applied to its input.
This voltage is delivered by low-pass filter.
V.3.2.4 - Divider stage
It is used to divide the VCO frequency (500kHz) by
32 so that it can be compared with the line sync
signal frequency of 15625Hz.
V.3.3 - Functional description of building blocks
V.3.3.1 - Phase comparator ” 1”
The comparator is functionally equivalent to a sig-
nal multiplier (see Figure 12).
Let’s assume that :
- i
then :
-
- the low-pass filter will suppress the 2f
Figure 12
10/46
i =
(see Figure 13)
LS
i
= I sin (
LS
2
IN
k
[ sin (
and
H
1.26V
t +
v 1 Signal
OUT
IN
Video Recognition
-
IN
.
VCR Mode
Switching
) and V
OUT
Mute
V CR
) + sin (2
OUT
1
= k cos (
H
t +
1
1mA
IN
H
2I
H
+
frequency
t +
OUT
V
+
CC
OUT
)]
i
LS
)
I
500 A
i
-
- the output current will be therefore proportionalto
In other words, the average current over one period
is :
I
I
The comparator conversion gain is thus :
A =
Later in our discussion we shall consider the two
possible values of the current I.
For the time being, let’s define these values as
follows :
- I = 500 A for ”long time constant” or normal
- I = 1.5mA for ”short time constant” VCR mode or
The values of A are therefore :
- A
- A
Use of comparator inhibition signal is quite useful
under noisy transmission conditions. It eliminates
risk of incorrect comparison during the line scan-
ning phase which would be due to the noise present
on LS signal. Horizontal phase and image stability
are thus highly enhanced.
Characteristics of this inhibition signal will be dis-
cussed at the end of this chapter.
AV
AV
component
sin (
the phase difference between the signals com-
pared.
operation
synchronization search (Mute).
1.26V
IN
LONG
SHORT
= 2I
&
T
-
i
H
IN
OUT
= I
T
=
Long 1 inhibition
= 0.16mA/rd
LS
-
H
t
= 0.47mA/rd
I
and t =
difference being low :
OUT
(in A/rd)
t
LS = 1
V I
2
S
i
O
IN
)
I+
I-
0
t - I
IN
-
T
2
t
S
OUT
H
t
2
t
S
t = 2I t
T
H