Desing and Implementation of a CMOS Interface for Non-Invasive Optical Biosensors-Edición Única
Eduardo Andrés Barredo Ochoa
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In this thesis, I propose an optoelectronic interface as those required in non-invasive micro sensors. The interface was implemented on a 0.35u.m CMOS technology and consists of a photodiode to capture and transform light into a current, and an amplifier to convert this current into a voltage level. I have designed three different photodiodes. Because of their structures, they are called p+/nwell, n+/p-substrate, nwell/p-substrate photodiodes. Additionally, I have implemented the spatially modulated technique in order to increase the photodiodes bandwidth. The required ring to avoid interference and to protect the input pads had also been incorporated in the layout. I have reviewed mathematical approximations that describe the photocurrent in the frequency domain. These approximations could be used in later studies aimed to characterize photodiode. Finally, the amplifier consists on a current to voltage conversion, a bandwidth expansion module and a voltage amplifier. The amplifier has showed a transimpedance of 47 ^/mj[, a frequency bandwidth of 852MHz and a gain-bandwidth of 2GHz.