Methods and apparatus for in-pixel filtering in focal plane arrays including apparatus and method for counting pulses representing an analog signal

A method for counting pulses representing an analog signal, the apparatus comprising:

• (A) producing a photocurrent, with at least one photodetector in a photodetector array, in response to detection of light;
• and
• (B) converting the photocurrent to a series of pulses with a converter in a unit cell in a plurality of unit cells operably coupled to the photodetector array;
• (C) counting first pulses in the series of pulses with a first counter in the unit cell in response to a first clock selection signal;
• and
• (D) counting second pulses in the series of pulses with a second counter in the unit cell in response to a second clock selection signal.

An apparatus for counting pulses representing an amplitude of optical radiation, the apparatus comprising:

• a plurality of photodetectors comprising at least one photodetector to produce an analog signal representing the amplitude of the optical radiation;
• and
• an integrated circuit operably coupled to the plurality of photodetectors, the integrated circuit comprising a plurality of unit cells, wherein at least one unit cell in the plurality of unit cells comprises:
• a converter to convert the analog signal from the at least one photodetector in the photodetector array to series of pulses;
• a plurality of counters comprising at least one counter, operably coupled to the converter, to count pulses in the series of pulses and to read-out a count representing the pulses in the series of pulses in response to a read-out clock;
• and
• a first multiplexer, operably coupled to the converter and to the at least one counter in the plurality of counters, to couple one of the series of pulses and the read-out clock to the plurality of counters in response to a clock selection signal.