Method for performing a tri-state comparison of two input signals in a window comparator circuit, and window comparator circuit for implementing the method

Abstract

A method performs a comparison of input signals in a window comparator circuit. In a first phase, input, ground and offset voltages are stored on capacitors. A comparison is performed between a first adapted input voltage and a second adapted input voltage added to an adapted offset voltage, to provide a first output signal. In a second phase, the voltages are stored on the capacitors in a different manner. A comparison is performed between the first adapted input voltage added to the adapted offset voltage and the second adapted input voltage, to provide a second output signal. Finally, a control of the state of the output signals is performed to determine if the comparison is in a low or high state if the output signals have a same low or high output level, or in an intermediate state if the output signals have a different output level.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method for performing a tri-state comparison of two input signals in a window comparator circuit. In particular said method can be applied for processing motion of a light detection circuit of an optical pointing device.[0002]The present invention concerns also the window comparator circuit for implementing the method for performing a tri-state comparison of two input signals. Said input signals can be signals from a pixel array, which picks up light reflected on a work surface.BACKGROUND OF THE INVENTION[0003]In the field of light detection in particular for a computer mouse with optical sensing device, it is actually necessary to improve the processing of the motion detection of said computer mouse on a work surface. The light reflected on the work surface has to be picked up by a pixel or photo-detector array in order to be processed in a motion detection processing circuit. A comparator array is placed between the pi...

AI Technical Summary

Benefits of technology

This approach enables efficient tri-state signal comparison with minimal components, easy programming of window voltage changes, and integration into a two-phase auto-zeroing comparator circuit, improving motion detection in optical pointing devices.

Problems solved by technology

For that it is generally not possible to conceive said window comparator circuit only with a simple comparator as usually in the light detection devices of the prior art.

Furthermore due to the number of signals to be compared in the comparator array, it is not feasible to implement 2-bit A / D converters or two simple comparators, in order to perform a window function for a window comparator circuit.

Given that two comparators are necessary to perform a comparison, said window comparator circuit is made with too many electronic components, which is a drawback.

Furthermore it is difficult to match accurately the two comparators to well define a tri-state comparison function, which is another drawback.

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