TDA4950 Datasheet, PDF (3/5 Pages) STMicroelectronics – TV EAST/WEST CORRECTION CIRCUIT

TDA4950
ELECTRICAL CHARACTERISTICS (Tamb = 25^oC, VS = 26 V, Vfr = 0, S1 and S2 in "a" position,
refer to test circuit unless otherwise specified) (continued)
Symbol
Parameter
K1
Parabola Coefficient
K2
Parabola Coefficient
∆V₇ (*)
I₈
V_SATL
V_SATH
V_F
Ifr
Current Source
Saturation Voltage
Saturation Voltage
Forward Voltage
Frame Sawtooth Current
Test Conditions
K₁
=
V_7A
V_7A
−
−
V_{7B ,}
V_7C
see
Figure
2
K₂
=
V_7A
V_7A
−
−
V_{7C ,}
V_7D
see
Figure
2
∆V₇ = V_7E – V_7F, see Figure 2
S1 → b
Io = 400 mA Sink S2 → b
Io = 100 mA Source S2 → c S1 → b
I_o = 400 mA
S2 → d S1 → b
Vfr = 6.6 VPP
Min. Typ. Max. Unit
0.28
0.71
– 40
40 mV
100
µA
1
2
V
0.8 1.5 V
1.2 1.7 V
66
µA
Figure 1 : Test CIrcuit
V_S
R7
R6
10kΩ
10kΩ
V_F
I_FR
7
6
V_SATH
2
a
V_FR
R2
S2
b
1 _TDA4950 5
R1
c
d
3
10kΩ
R3
4
8
11kΩ
V_REF
I_F
-I_O
R8
20kΩ
I_O
V_SATL
b
a
S1
Figure 2 : Parabola Characteristics
V₇ (V)
V_7A
V_7B
V_7C
V_7D
V_7E
-60
36
0 15 30
V_7F
60 I_FR (µA)
CIRCUIT OPERATION
(see the shematic diagram)
A differential amplifier OP1 is driven by a vertical
frequency sawtooth current of ± 33µA which is
produced via an external resistor from the sawtooth
voltage. The non-inverting input of this amplifier is
connected with a reference voltage corresponding
to the DC level of the sawtooth voltage. This DC
voltage should be adjustable for the keystone cor-
rection. The rectified output current of this amplifier
drives the parabola network which provides a para-
bolic output current. This output current produces
the corresponding voltage due to the voltage drop
across the external resistor at pin 7.
If the input is overmodulated (> 40µA) the internal
current is limited to 40µA. This limitation can be
used for suppressing the parasitic parabolic current
generated during the flyback time of the frame
sawtooth.
A comparator OP2 is driven by the parabolic cur-
rent. The second input of the comparator is con-
nected with a horizontal frequency sawtooth
voltage the DC level of which can be changed by
the external circuitry for the adjustment of the pic-
ture width.
The horizontal frequency pulse-width modulated
output signal drives the final stage. It consists of a
class D push-pull output amplifier that drives, via
an external inductor, the diode modulator.
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