9-4
(2) Linearity Correction (LIN)
(2-1) S-curve Correction (S Capacitor)
Pictures are expanded at left and right ends of the screen even
if a sawtooth current with good linearity flows in the deflection
coil when deflection angle of a picture tube increases. This is
because projected image sizes on the screen are different at
screen center area and the circumference area as shown in
Fig. 4. To suppress this expansion at the screen circumference,
it is necessary to set the deflection angle to a large value
(rapidly deflecting the electron beam) at the screen center
area, and to set the deflection angle to a small value
(scanning the electron beam slowly) at the circumference
area as shown in Fig. 4.
In the horizontal output circuit shown in Fig. 5, capacitor Cs
connected in series with the deflection coil LH is to block DC
current. By properly selecting the value of Cs and by
generating a parabolic voltage developed by integrating the
deflection coild current across the S capacitor, and by varying
the deflection yoke voltage with the voltage, the scanning
speed is decreased at beginning and end of the scanning, and
increased at center area of the screen. The S curve correction
is carried out in this way, thereby obtaining pictures with
good linearity.
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