Noise reduction in AC-coupled amplifiers

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dc.contributor	Universitat Politècnica de Catalunya. Departament d'Enginyeria Electrònica
dc.contributor	Universitat Politècnica de Catalunya. GRUP ISI - Grup d'Instrumentació, Sensors i Interfícies
dc.contributor.author	Serrano Finetti, Roberto Ernesto
dc.contributor.author	Pallàs Areny, Ramon
dc.date	2014-07-01
dc.identifier.citation	Serrano, R.; Pallas, R. Noise reduction in AC-coupled amplifiers. "IEEE transactions on instrumentation and measurement", 01 Juliol 2014, vol. 63, núm. 7, p. 1834-1841.
dc.identifier.citation	0018-9456
dc.identifier.citation	10.1109/TIM.2014.2299525
dc.identifier.uri	http://hdl.handle.net/2117/26329
dc.description.abstract	AC-coupled amplifiers are noisier than dc-coupled amplifiers because of the thermal noise of the resistor(s) in the ac-coupling network and the increased contribution of the amplifier input noise current i(n). Both contributions, however, diminish if the corner frequency f(c) of the high-pass filter observed by the signal is lowered, the cost being a longer transient response. At the same time, the presence of large resistors in the ac-coupling network suggests that the use of FET-input amplifiers will be advantageous because i(n) is smaller than in bipolar amplifiers. However, the noise floor, defined as that for a dc-coupled amplifier, can be larger for FET-input amplifiers because of their higher input voltage noise. Therefore, there is no clear criterion to decide which amplifier type is quieter. In this paper, we propose the quotient between the high-pass frequency of the signal bandwidth (f(L)) and f(c) (K = f(L)/f(c)) as quantitative design parameter to reduce the additional noise contributed by a first-order ac-coupling network as compared with dc coupling. Using this parameter noise is greatly reduced without unnecessarily lengthening the transient response that results from the use of common qualitative design criteria. We demonstrate that relatively large K values yield total noise closer to the noise floor, hence it is better not to determine f(L) at the front amplifier stage but later on in the signal chain. Furthermore, a large K value permits bipolar op-amps to achieve lower noise than FET amplifiers even for capacitive signal sources, provided amplifier biasing is guaranteed.
dc.language.iso	eng
dc.relation	http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6728674
dc.rights	info:eu-repo/semantics/openAccess
dc.subject	Àrees temàtiques de la UPC::Enginyeria electrònica::Instrumentació i mesura
dc.subject	Amplifiers (Electronics)
dc.subject	AC coupling
dc.subject	AC-coupling networks
dc.subject	capacitance output sensors
dc.subject	fast Fourier transform noise measurement
dc.subject	high-pass filters
dc.subject	noise reduction
dc.subject	op-amp noise
dc.subject	resistive sensors
dc.subject	voltage amplifiers
dc.subject	Amplificadors
dc.subject	Elèctrodes
dc.subject	Soroll -- Mesurament
dc.title	Noise reduction in AC-coupled amplifiers
dc.type	info:eu-repo/semantics/publishedVersion
dc.type	info:eu-repo/semantics/article

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