A new current mode APS in 0.18 μm standard CMOS process for smart image sensors

In this paper we present a new current mode structure for active pixel sensor (APS) which is an essential part in fast parallel processing Smart CMOS Image Sensors such as wireless capsule endoscopy. Using two diodes (N+/P-Well and P-Well/Deep-N-Well) in parallel like a pinned photo-diode (PD) improves sensing of optical signal and thus leads to higher sensitivity than a conventional PD. Also integrated signal amplification inside the collection area of the pixel increases the sensitivity of the device due to the amplification in the pixel. The proposed structure with regards to using Deep-N-Well/P-Substrate junction as a guard ring, suppresses the pixel cross-talk highly. In pixel delta reset sampling helps to make feasible on-chip parallel processing. A test structure, consist of 8 × 8 pixels of the proposed current mode APS has been simulated by standard 0.18 μm RF-CMOS technology of TSMC with a 21 × 23 μm2 pixel size. Fill factor of the pixel is 24 %.