| 摘要 |
A method of and apparatus for selectively engaging an internal trap filter (20) and implementing an external trap filter through a single pin (10) routes a separate luminance signal through the pin (10) or through an internal trap filter (20) based on the logical voltage level at the pin (10). When implementing an external trap filter the external components comprising the filter are coupled between the pin (10) and ground and a voltage level of the pin (10) is maintained at a logical low voltage level. When the pin (10) is at a logical low voltage level, two path switches (22 and 24) are closed and the separate luminance signal is routed through the pin (10) to be filtered by the external trap filter. The internal trap filter (20) is engaged by coupling a precision resistor (80) between the pin (10) and a power supply voltage thereby pulling the voltage level of the pin (10) to a logical high voltage level and opening the two path switches (22 and 24) to bypass the pin (10) and route the separate luminance signal through an internal trap filter (20). When the voltage level of the pin (10) is at a logical high voltage level, a bias switch (26) is closed thereby providing a bias current, created from the voltage drop across the precision resistor (80), to the internal trap filter (20). The internal trap filter (20) is activated by the bias current and filters the separate luminance signal according to the value of the bias current, before the separate luminance signal is combined with the separate chrominance signal. The value of the bias current is controlled by the value of the precision resistor (80). |
