Low power operation of differential image sensor pixels

A method for operating a sensor array including a plurality of differential pixels, the method comprising:

• operating a first differential pixel of the sensor array in a first, lower power mode;
• supplying a first clock signal to selectively activate a first collection terminal of the first differential pixel for a first duration;
• supplying a second clock signal to selectively activate a second collection terminal of the first differential pixel for a second duration;
• reading out a first amount of charge accumulated at the first collection terminal over the first duration;
• reading out a second amount of charge accumulated at the second collection terminal over the second duration;
• comparing the first amount of charge and the second amount of charge in an analog domain;
• and
• responsive to the first amount of charge being different from the second amount of charge by more than a threshold, operating the first differential pixel of the sensor array in a second, higher power mode,
• wherein the threshold is based on the first amount of char e and the second amount of charge.

An imaging system comprising:

• a sensor array including a plurality of rows of differential pixels;
• and
• a controller configured to:
• operate each active differential pixel of the sensor array in a first, lower power mode;
• supply a first clock signal to selectively activate a first collection terminal of each active differential pixel for a first integration duration;
• during a first read duration following the first integration duration, for a first subset of rows of differential pixels, readout a first amount of charge accumulated at the first collection terminal over the first integration duration, and for a second subset of rows of differential pixels, maintain the amount of charge accumulated at the first collection terminal over the first integration duration;
• supply a second clock signal to selectively activate a second collection terminal of each active differential pixel for a second integration duration, the second clock signal substantially complementary to the first clock signal;
• during a second read duration following the second integration duration, for the second subset of rows of differential pixels, readout the first amount of charge accumulated at the first collection terminal over the first integration duration, readout a second amount of charge accumulated at the second collection terminal over the second integration duration, and for the first subset of rows of differential pixels, maintain the amount of charge accumulated at the second collection terminal over the second integration duration;
• for each differential pixel, compare the first amount of charge and the second amount of charge in an analog domain;
• and
• for a first differential pixel, responsive to the first amount of charge being different from the second amount of charge by more than a threshold, operate the first differential pixel of the sensor array in a second, higher power mode.