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

Abstract

Digital focal plane arrays (DFPAs) with multiple counters per unit cell can be used to convert analog signals to digital data and to filter the digital data. Exemplary DFPAs include two-dimensional arrays of unit cells, where each unit cell is coupled to a corresponding photodetector in a photodetector array. Each unit cell converts photocurrent from its photodetector to a digital pulse train that is coupled to multiple counters in the unit cell. Each counter in each unit cell can be independently controlled to filter the pulse train by counting up or down and/or by transferring data as desired. For example, a unit cell may perform in-phase/quadrature filtering of homodyne- or heterodyne-detected photocurrent with two counters: a first counter toggled between increment and decrement modes with an in-phase signal and a second counter toggled between increment and decrement modes with a quadrature signal.