University of Pennsylvania

Zheng Yang

Jan Van Der Spiegel

Viktor Gruev

A CMOS image sensor that is capable of both voltage- and current-mode operations selects the mode based on the position of mode switches. Each pixel on the imager has a single transistor acting as either source follower for voltage readout, or transconductor for current readout. The two modes share the same readout lines, but have their own correlated double sampling (CDS) units for noise suppression. A current-mode readout technique using a velocity-saturated short-channel transistor may be used to achieve high linearity. An image array may be formed as a mixture of 3 types of pixels with identical photodiodes and access switches. The readout transistors are optimally sized for their designated mode of operation. Alternatively, two readout transistors are provided per pixel, each individually optimized for the desired mode of operation.

CMOS linear voltage/current dual-mode imager

A voltage and current mode active pixel sensor for high resolution imaging is presented. The photo pixel is composed of a photodiode and two transistors: reset and transconductance amplifier transistor. The switch transistor is moved outside the pixel, allowing for lower pixel pitch and increased linearity of the output photocurrent. The reset and amplifier (readout) transistors may also be shared among adjacent pixels by the introduction of transfer switches between the photodiodes and the source of the reset transistor and the gate of the readout transistor. The switch transistor outside the pixels provides biasing voltages or currents to the readout transistors to selectively turn them on when readout of the corresponding photodiode is desired and turns the readout transistor off when the corresponding photodiode is not to be read out. The increased linearity of the image sensor has greatly reduced spatial variations across the image after correlated double sampling and the column fix pattern noise is greatly improved.

Growing community of inventors

Philadelphia, PA, United States of America

Zheng Yang