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A 33 µW Sub-3 dB Noise Figure Low Noise Amplifier for Medical Ultrasound Applications
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Electronics and Telecommunications.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]

The low noise amplifier is a critical part of most high performance ultrasound receivers, and is important for achieving high sensitivity and a wide dynamic range. By having a large gain in the low noise amplifier, the total noise of the receiver system will be dominated by that of the amplifier. For most low noise amplifier, there is a fundamental trade–off between accuracy and power consumption, which makes it difficult to design micro power front–end amplifiers with excellent noise performance. In some cases, however, lower accuracy can be tolerated if the source itself is noisy. This is the case for small, high impedance sources, where the noise level is in the region of 18 nV/sqrt{Hz}. This thesis presents the design and simulations of a low noise amplifier in standard 180 nm CMOS suitable for use with high impedance sources. In fact, high impedance sources pose challenges on the biasing of voltage amplifiers, where maintaining high input impedance is necessary. In addition, for differential amplifiers, implementing common–mode feedback will typically result in a significant increase in power consumption and area overhead. To alleviate this problem, a switched common–mode feedback scheme is implemented, that also provide high input impedance biasing of the input transistors. In order to cope with the large dynamic range requirement inherent in many ultrasound modalities, variable gain is often used to compress the dynamic range for the analog front–end. Methods for adding variable gain without resulting in a large increase in area and power consumption is therefore of huge interest in many ultrasound applications. Several methods of adding variable gain is investigated in this thesis, and a capacitive attenuator is proposed, which causes minimum increase in noise factor, while increasing the gain range by at least 20 dB. Large scale integration of several thousands analog front–ends in a single ultrasound probe handle requires low power consumption and minimum area overhead for all parts of the analog front–end, including the low noise amplifier. By using a figure–of–merit based optimization technique, the designed amplifier topology achieves an low power consumption of 17.3 μA, while maintaining a noise factor of less than 3 dB at resonance. In addition to performing a single–ended to differential conversion, this amplifier realizes a maximum voltage gain of 23.4 dB, with a 3 dB bandwidth of 21.5 MHz.

Place, publisher, year, edition, pages
Institutt for elektronikk og telekommunikasjon , 2011. , 107 p.
Keyword [no]
ntnudaim:5836, MTEL elektronikk, Analog og blandet design
URN: urn:nbn:no:ntnu:diva-14178Local ID: ntnudaim:5836OAI: diva2:448156
Available from: 2011-10-14 Created: 2011-10-14

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