Breast cancer is one of the most common diseases affecting women and the mortality rate is very high in Bangladesh, mainly due to the lack of early diagnosis. X-ray mammography is not available widely in Bangladesh, besides it has an associated biological hazard. Multi-frequency bio-impedance measurement or bio-impedance spectroscopy has a great potential in many biomedical applications including breast cancer screening which involves tissue characterization. In Bio-impedance spectroscopy a range of frequencies of low level current is injected to the human body and corresponding bio-impedance is measured. In a typical bio-impedance measurement system an ac source with a constant current amplitude is an essential part in which the current amplitude should not change with frequency or load, the latter being typically of the order of a few kilo ohms in the human body. The constant current source is usually obtained from a voltage-to-current converter and several standard designs are available, for example a floating current source, a Howland current source and an enhanced Howland current source. The present work was taken up to perform a comparative study of these three types of current sources based on a commonly available low cost operational amplifier, 741. It was found that the enhanced Howland current source gave the best performance, the current being almost constant up to a frequency of about 10kHz for a load of 10k?. This work gives an understanding of this fundamental circuit segment that is essential for the development of a Bioimpedance Spectroscopy system. DOI: http://dx.doi.org/10.3329/bjmp.v5i1.14671 Bangladesh Journal of Medical Physics Vol.5 No.1 2012 71-76

Recent advancements in sensor technology, wireless networks and consequently wireless sensor networks and the increase of their applications in different fields have led to their great importance. One of the most important challenges is the management of huge amount of data produced by sensors in network in order to reduce data traffic in network and minimize the energy consumption. This paper gives a survey on different data fusion techniques dividing them into two main groups: structured and structure-free. The main properties of structured approaches are discussed and the motivations to introduce structure-free approaches are emphasized via describing the shortcomings of structured approaches.

In this paper, a low-voltage low-power CMOS operational amplifier using the composite cascode technique is presented. This technique has been employed in the differential input pair and output transistors to enhance the gain of op-amp. Also, indirect compensation is used to improve the frequency response of the op-amp and avoids instability when a large capacitive load at the output of the op-amp must be handled. Two-stage op-amp is designed and simulated in a TSMC 0.18 μm CMOS technology, to evaluate the proposed technique. The sub-threshold region is employed in the design to use the low supply voltage and reduce power consumption effectively. The op-amp operates at a 0.7 V power supply with 891 nW power consumption. The open-loop gain is 90.1 dB, the unity gain-bandwidth (UGBW) is 309 kHz, and the phase margin is 57.6 degree under 15 pF load.

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