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In this paper, limitations of two-phases lock-in amplifiers (LIAs) in variable frequency applications are reported. Given those limitations, an alternative LIA architecture is described: the heterodyne LIA. Design strategies for improving general performance of heterodyne LIA without sacrificing power consumption have been described. Comparative simulations of both architectures have been carried...
A power-efficient wideband zero-crossing phase angle detector for bioelectrical impedance measurement is described. The detector consists of a pair of instrumentation amplifiers, two identical limiting amplifiers, and digital circuitry that compensates for offset errors introduced by the analog blocks. Designed in a 0.35-µm CMOS process and at a 2-V supply, the proposed phase detector measures the...
In most bioelectrical acquisition systems, there is the need for amplifying small differential voltages. This paper describes a CMOS instrumentation amplifier (IA) based on the principle of current feedback for use in biological tissue characterization by bioelectrical impedance measurement. The constraints on the design of IA's for wideband operation are addressed. An approach that can be exploited...
A power-efficient CMOS limiting amplifier to be used as a basic building block for bioelectrical impedance phase angle measuring devices is presented. The limiting amplifier is intended for use in a wearable device for malnutrition status assessment. A high-sensitivity limiting amplifier tolerant of process spreads and mismatches was fabricated in 0.35-µm CMOS technology. The circuit was designed...
In this paper, a circuit technique—common-mode (CM) response overlapping—for maintaining the small-signal behavior of rail-to-rail amplifiers nearly constant over the whole input CM range, is introduced. This technique modifies the CM response of the rail-to-rail input stage adequately by means of two constant input floating voltage sources, which are adjusted by using a static tuning section. Its...
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