Pixel sensors using nonlinear capacitance with logarithmic characteristics

Abstract

Disclosed herein is an active pixel sensor having a first transistor amplifying voltage generated in response to light at an integration node; a second transistor selects a specific pixel from a pixel array; a third transistor resets voltage of the integration node to voltage supplied from VDD during a reset period; a fourth transistor connects a photogate capacitance to the integration node increasing a dynamic range when the voltage of the integration node is VDD-Vth; a fifth transistor generates a signal voltage in a logarithmic response to light when the voltage of the integration node is logarithmic bias voltage-Vth; and a photodiode to convert photons into electron pairs in a depletion layer, causing signal charges to be accumulated when light is incident from outside.