Integrating a Temperature Sensor into a CMOS Image Sensor

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Dark current noise in image sensors is highly sensitive to temperature, and a difference in temperature in image sensors can be seen in the image as a non-uniform noise source. Many CMOS image sensors are integrated in mobile devices and lack a physical shutter to generate dark frame subtraction to compensate for dark current noise. In this thesis, the design and implementation of a bandgap based temperature sensor into an image array is proposed. A single parasitic pnp BJT, together with a source follower and control switches, is integrated inside an image array and is biased from outside the array. By means of CDS in the column amplifier of the imager, the difference in base-emitter voltage of a single BJT, that is being biased by a known current ratio, can be measured to calculate temperature. A total of 542 temperature sensors are fully integrated in a 192x64 test array of 4T APS based pixels and share the same readout as the image pixels. At the moment of writing, the chip was still waiting for tape-out and no measurement results can be presented in this thesis.