| 摘要 |
A television system comprises a first input terminal (20) for providing a composite video (CSCC) signal or a separated luminance (SCC) signal, and a second input terminal (15) for providing a separated chrominance (C) signal. A change-over switch (11) has a first input (a) coupled to the first input terminal (20) through a path including a color sub-carrier filter (9), a second input (b) coupled to the second input terminal (15) through a path not including the color sub-carrier filter (9), and an output (c) coupled to the input (d) of a color decoder (8). The change-over switch couples the input (d) of the color decoder (8) to the first input terminal (20) in a first position (a), and couples the input (d) of the color decoder (8) to the second input terminal (15) in a second position (b). A sub-carrier detector (CK) is coupled to the output (c) of the change-over switch (11) for detecting the presence or absence of a color sub-carrier. A control unit initially causes the change-over switch ( 11) to be in the first position (a) and thereafter causes said change-over switch (11) to remain in the first position (a) if a color sub-carrier is present at the output (c) of the change-over switch (11), but causes the change-over switch (11) to be in the second position (b) if a color sub-carrier is not present. Once the change-over switch (11) is in the second position (b), the control unit (1) causes said change-over switch (11) to be switched back to said first position (a) from said second position (b) if a color sub-carrier is still not present.
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