Computer navigation devices

1. A method for detecting whether an optical mouse is in contact with a working surface, the optical mouse comprising an image sensor and a motion output, the method comprising:

imaging the working surface with the image sensor for providing signals corresponding to the image;

analyzing the signals corresponding to the image for determining whether the image contains no in-focus object by

summing an output of at least a majority of each frame of the image,

comparing the summed output of each frame of the image to a threshold, and

assessing each frame of the image based upon the comparing; and

disabling the motion output when no in-focus object is found.

2. A method according to claim 1 , further comprising high pass filtering the signals before being analyzed.

3. A method according to claim 2 , wherein the optical mouse further comprises a correlation circuit and a motion estimation circuit connected thereto; and further comprising applying filtered signals to the correlation circuit for correlating successive frames of the image, with the correlating providing an input to the motion estimation circuit.

4. An optical mouse comprising:

an image sensor for forming an image of a working surface on which the optical mouse is used;

a motion signal circuit for processing the image from said image sensor for providing an output signal representing motion of the optical mouse on the working surface; and

a lift-off detection circuit connected to said image sensor and to said motion signal circuit for

detecting the optical mouse being lifted away from the working surface,

determining whether the image contains no in-focus object, and

disabling the output signal during lift-off based upon the determining;

said lift-off detection circuit comprising a summer for summing an output of at least a majority of each frame of the image, and a comparator for comparing the summed output of each frame of the image with a threshold, and for assessing each frame based upon the comparing.

5. An optical mouse according to claim 4 , further comprising a high-pass filter between said image sensor and said summer.

6. An optical mouse according to claim 5 , wherein said motion signal circuit is connected to an output of said high-pass filter.

7. An optical mouse according to claim 6 , wherein said motion signal circuit comprises:

a correlation circuit for measuring correlation of successive image frames; and

a motion estimation circuit deriving a motion signal from the correlation.

8. An integrated circuit comprising:

an image sensor comprising an array of pixels for forming a picture signal of a working surface based upon pixel values;

an analog-to-digital converter for converting the picture signal to a digital format;

an image processor for correlating successive frames of the picture signal; and

a lift-off detector connected between said analog-to-digital converter and said image processor and comprising

a summer for summing an output of at least a majority of each frame of the picture signal, and

a comparison circuit for comparing the summed output of each frame of the picture signal with a threshold.

9. An integrated circuit according to claim 8 , wherein said image sensor, said analog-to-digital converter, said image processor and said lift-off detector are formed using CMOS technology.

10. An integrated circuit according to claim 8 , further comprising a high-pass filter between said image sensor and said summer.

11. An integrated circuit according to claim 10 , wherein said image processor is connected to an output of said high-pass filter.

12. An integrated circuit according to claim 8 , wherein said image processor comprises:

a correlation circuit for measuring correlation of successive image frames of the picture signal; and

a motion estimation circuit for providing a motion signal based upon measured correlation of the successive image frames of the picture signal.