Tomohisa Ishida

4.1-megapixel JFET imaging sensor LBCAST

A new type of imaging sensor suitable for digital SLR cameras has been developed. Each pixel in the sensor comprises a buried photodiode, a junction field-effect transistor (JFET), a transfer gate, two reset gates, and a reset drain. The JFET receives signal charge directly from the buried photodiode through the transfer gate and outputs the converted voltage signal, while the reset gate together with the reset drain controls both resetting and selecting operations of the JFET. The pixel does not have a floating diffusion nor a row select gate, resulting in a simplified structure, an increased fill factor and a better production yield. Another feature of the sensor is the parallel readout scheme. Signals from green pixels arrayed in a checker pattern are read out from one output terminal, while those from red and blue pixels are read out, row-by-row, from the other output terminal. This enables high-speed readout without introducing fixed pattern noise. Total and effective pixel numbers are 4.26 and 4.08 mega respectively. A pixel size is 9.4um square with a fill factor of 36%. Power consumption is 600mW under consecutive operation mode of 9.3 frames/sec. Saturation output voltage is 700mV with a noise floor of 0.20mVrms, having a dynamic range of about 70dB including the camera system.