NOISE EQUIVALENT TEMPERATURE DIFFERENCE PERFORMANCE OF AN IR DETECTOR IN A HYBRID FOCAL-PLANE ARRAY

Theoretical expressions to calculate the signal-to-noise ratio of an IR detector in a direct injection readout hybrid focal plane array (FPA) are developed in this paper. The theory takes into account the effect of shift of operating point of the pixel with small variations in scene temperature and contribution of shunt resistance due to surface leakage currents in the photodiode. These expressions are then used to calculate the noise equivalent temperature difference (NETD) performance of the IR detector in the FPA. The role of buffered direct injection (BDI) circuit in improving the NETD performance of hybrid pixels in a LWIR mercury cadmium telluride FPA array is analyzed. The results of our calculations show that the individual pixels in a LWIR HgCdTe FPA would not function to their ultimate performance and in certain conditions may even exhibit erratic behaviour in the absence of BDI interface.