Solid-state image sensor with focal-plane digital photon-counting pixel array

A solid-state photon-counting imaging device for ultralow light level detection comprising:

• a layer of photosensitive material;
• a source of reference potential;
• a source of reference voltage charge;
• an N.times.V array of photodetector diodes arranged in rows and columns in said layer of photosensitive material where each separate number N represents an integral number of rows and columns of photodetector diodes in said array and the number N of rows is independent of the number N of columns, each photodetector diode having a first terminal and a second terminal, said first terminal of every photodetector diode being connected to said source of reference potential;
• control means for generating separately cyclical reset clock pulses and select clock pulses separated in time by a predetermined interval;
• an array of high gain, low noise unit cells, one unit cell for each photodetector diode in every row of said N.times.N array of photodetectors in a VLSI focal-plane array on said layer of photosensitive material, each unit cell having an input terminal, a high-gain voltage amplifying means, a select switch, and an output terminal connected in series, and in that order, said input terminal of each unit cell being connected to said second terminal of a respective one of said photodetector diodes, and each unit cell further having a reset switch responsive to said reset clock pulses for resetting a voltage charge of input capacitance at said input terminal to a reference voltage charge common to all of said unit cells;
• an array of digital counters, one digital counter for each photodetector diode in at least one row, each digital counter connected to said output terminal of a respective cell unit for counting voltage pulses occurring at said output terminal;
• whereby each unit cell is prepared by said reset pulse for a possible event of a photon incident on a respective one of said photodetector diodes producing a photoelectron increased voltage charge of said input capacitance, said increased voltage charge being automatically amplified by said voltage amplifying means in order for it to be sampled through said select switch in response to said select pulse closing said select switch, thereby producing at said output terminal of a unit cell connected to a respective photodetector diode a voltage pulse to be counted by a respective one of said digital counters.