Sub-carrier detection (SCD) for motion threshold logic

1. An apparatus, comprising:

a video decoder configured to receive a composite video signal modulated on a sub-carrier signal and having a luma component and a chroma component, the video decoder configured to perform a motion detection operation on the luma component and the chroma component in a plurality of frequency regions respectively;

variable threshold logic, coupled to the video decoder, and configured to provide a unique threshold value to the video decoder for each of the plurality of frequency regions respectively; and

a sub-carrier detection logic, coupled to the variable threshold logic, and configured to detect the sub-carrier signal by checking both spatial and temporal characteristics of the sub-carrier detection logic.

2. The apparatus of claim 1 , wherein the sub-carrier detection logic is configured to receive a first frame, a second frame and a third frame, wherein the first frame is a current frame, the second frame is a previous frame with respect to the current frame, and the third frame is prior to the previous frame.

3. The apparatus of claim 1 , wherein the sub-carrier detection logic is configured to check the temporal chroma component of the sub-carrier signal by analyzing the chroma amplitude across a first frame and a second frame of the sub-carrier signal and then across a single frame of the sub-carrier signal.

4. The apparatus of claim 1 , wherein the sub-carrier detection logic is configured to check the temporal chroma component of the sub-carrier signal by analyzing the temporal polarity of the sub-carrier signal.

5. The apparatus of claim 2 , wherein the sub-carrier detection logic further includes:

a first band pass filter, a second band pass filter, and a third band pass filter configured to receive the first frame, the second frame and the third frame respectively; and

a first delay element, a second delay element and a third delay element configured to receive outputs from the a first band pass filter, a second band pass filter, and a third band pass filter and configured to store four adjacent samples of the first frame, the second frame and the third frame respectively.

6. The apparatus of claim 1 , wherein the sub-carrier detection logic further comprises:

a band pass filter configured to receive the composite vide signal;

four delay elements, coupled to the band pass filter, and configured to store four samples from the band pass filter respectively;

a first summation device configured to sum the stored samples in the first and the third delay elements;

a second summation device configured to sum the stored samples in the second and fourth delay elements;

a rectifier element configured to rectify and compare the output of the first and the second summation devices with a threshold voltage;

a first logic circuit configured to generate a first signal of a first logic state if the outputs of the two summation devices are less than the threshold voltage;

a second logic circuit configured to generate a second signal of the first logic state if alternate samples from the four delay elements are of the opposite logic state; and

a third logic circuit configured to generate a chroma status signal if the first signal and the second signal are of the first logic state.

7. The apparatus of claim 1 , wherein the sub-carrier detection logic is further configured to detect line chroma characteristics of the composite video signal, the sub-carrier detection logic further comprising:

a first band pass filter, a second band pass filter and a third band pass filter configured to receive a first line, a second line and a third line of the composite video signal;

a first delay element, a second delay element and a third delay element coupled to the first band pass filter, the second band pass filter and the third band pass filter respectively, the first delay element, the second delay element and the third delay element configured to store four line samples each; and

a logic circuit configured to receive the stored line samples in the first delay element, the second delay element and the third delay element and to generate a line chroma signal.

8. The apparatus of claim 1 , wherein the sub-carrier detection logic is further configured to generate and provide a control signal to the variable threshold logic to control the unique threshold value for motion detection.

9. The apparatus of claim 1 , wherein the sub-carrier detection logic is further configured to check the temporal sub-carrier signal characteristics across frames of the composite video signal.

10. The apparatus of claim 1 , wherein the sub-carrier detection logic is further configured to check the spatial sub-carrier characteristics across lines defined by the composite video signal.