Method, sensing device and optical pointing device including a sensing device for comparing light intensity between pixels

In an optical pointing device, a method for comparing light intensity between pixels of a photodetector array, each of said pixels comprising a photosensitive element generating a sensed output signal in response to radiation, this method comprising the steps of:

• integrating said sensed output signals over time to provide an integrated signal for each of said photosensitive elements;
• integrating a first sensed output signal of a first pixel until, the end of a first time period and storing the resulting first integrated signal;
• continuing the integration of a second sensed output signal of a second pixel until the end of a second time period to provide a second integrated signal;
• and
• comparing said first and second integrated signals to provide an output signal representative of an edge condition between said first and second pixels,
• wherein integration of said second sensed output signal is continued until the end of said second time period or until the end of a third time period shorter than said second time period depending on a previous state of said output signal,
• wherein said output signal is at a first state, respectively second state, if said first integrated signal is greater, respectively lower, than said second integrated signal, and wherein:
• if said output signal is at said first state, integration of said second sensed output signal is continued until the end of said third time period;
• and
• if said output signal is at a said second state, integration of said second sensed output signal is continued until the end of said second time period.

A sensing device for an optical pointing device comprising a plurality of pixels including a first and a second pixel aligned along a first axis, each one of said pixels comprising:

• a photosensitive element for generating a sensed output signal in response to radiation;
• and
• an integrating circuit connected to said photosensitive element for integrating said sensed output signal over time and for outputting a resulting integrated signal,
• said sensing device further comprising first comparator means for comparing light intensity between said first and second pixels and for determining if a first edge condition exists between said first and second pixels,
• wherein said first comparator means comprise a first comparator circuit having one comparator input connected to the integrating circuit of said first pixel and another comparator input connected to the integrating circuit of said second pixel,
• said sensing device further comprising:
• means for resetting said integrating circuits during a resetting period and for releasing these integrating circuits during an integration period;
• means for disconnecting a first comparator input of said first comparator circuit from the corresponding integrating circuit at the end of a first time period;
• means for storing the resulting integrated signal on the disconnected first comparator input of said first comparator circuit;
• and
• means for latching said first comparator at the end of said integration period.