FPN Attenuation by Reset-Drain Actuation in the Linear-Logarithmic Active Pixel Sensor

The three FET CMOS active pixel sensors (APS) operating in the linear-logarithmic mode is one of the most efficient wide-dynamic-range imagers. However, the quality of the image generated at the focal-plane array is often compromised by fixed-pattern noise (FPN) between pixels. The classical correlated double sampling (CDS) technique is used to reduce FPN in imagers operating in the linear mode. But in the complementary linear-logarithmic mode CDS does not work properly and alternative techniques must be applied to reduce FPN. The ordinary alternative techniques increase either the complexity of the pixel or its external circuitry. In order to avoid these problems a new technique was devised to reduce FPN that can be applied to the basic three FET APS architecture. With the purpose to assert the efficacy of the proposed technique a small array was fabricated in a standard 0.35 μm CMOS technology. Experimental results show that the proposed technique is able to reduce FPN quite steadily within the whole illumination range used to test the array. And therefore, the signal-to-noise-and-distortion ratio (SNDR) of the array is also improved within the whole range of operation.