The infrared imaging system has been developed for more than 50 years, from the early stage the scanned imaging
system using single unit detector to imaging system using focal plane detector arrays. For focal plane array detectors, the
readout circuit is used to read the photon detector signal out. Charge coupled device had been used for the readout of the
focal plane array detectors and currently CMOS technology is used. In this paper, readout circuit design using CMOS
technology for infrared focal plane array detectors is reviewed. As an interface between the detector and the image signal
processing circuits, readout circuit is a critical component in the infrared imaging system. With the development of the
CMOS technology, the readout circuit is now moving into the CMOS technology. With the feature size scaling down,
the readout cell size is reduced, which enable us to integrate more complex circuits into the readout cell. From the system
point of view, different requirements and specifications for the CMOS readout circuit are analyzed and discussed.
Different readout circuit parameters such as injection efficiency, dynamic range, noise, detector biasing control, power
consumption, unit cell area, etc are discussed in details. Performance specifications of different readout cell structures
are summarized and compared. Based on the current mirroring integration readout cell, a fully differential readout cell is
proposed. The injection efficiency of this proposed readout cell is very close to unity and the detector biasing voltage is
close to zero. Moreover, the dynamic range of the proposed readout cell is increased and the rejection on interference is
improved because of the fully differential structure. All these are achieved without much power consumption increasing.
Finally, a full digital readout circuit concept is introduced. By employing a current controlled oscillator, the photocurrent
is converted to frequency and integrated in digital domain and the final output is digital signal.