One of the most important directions for the research in analog integrated circuit is the design of low-voltage low-power structures working in battery-operated portable systems, hearing equipment and, in particular, in sensor applications. A low-voltage input and output rail-to-rail integrated CMOS Operational Transconductance Amplifier (OTA) has been here considered. Its topology has been optimized for the lowest supply voltage compatible with the used technology (threshold voltages of about 0.75 V). The input and output full swing characteristic is important when the amplifier is used in a follower configuration or in front-end circuits, where the signal comes directly from the sensor. In our case, the range of the sensor response is not absolutely limited by the amplifier. This OTA differs from others appeared in literature (working at least at 1.8 V of supply voltage) for its constant-g_m input stage which ensures a constant gain-bandwidth product over the input common mode voltage and, consequently, a simple frequency compensation. This work will consider an application of the CMOS OTA oriented towards capacitive sensors whose use is rather spread in many sensing systems.
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