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An ultra-low noise fully-differential amplifier
  • Enrique M. Spinelli,
  • Marcelo A Haberman
Enrique M. Spinelli
Faculty of Engineering, Institute of Industrial Electronics, Control and Instrumentation (LEICI), GIBIC, La Plata National University

Corresponding Author:[email protected]

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Marcelo A Haberman
Faculty of Engineering, Institute of Industrial Electronics, Control and Instrumentation (LEICI), GIBIC, La Plata National University

Abstract

A general-purpose instrumentation amplifier must be dc-coupled and have a differential input to handle both differential and single-ended input signals. It also must exhibit low input noise in both voltage and current, to accommodate a wide range of signal source impedances. Additionally, having a differential output is desirable to allow direct connection to current high-resolution analog-to-digital converters (ADCs) which have differential inputs. There are commercially available devices with \(e_n\) voltage noise spectral densities as low as 1 nV √Hz ⁄ but present high \(e_n\) current noise spectral densities \(i_n\) of a few pA/√Hz. On the other hand, there are also devices with \(i_n\) as low as a few fA/√Hz but presenting  \(e_n\)   around 10 nV/√Hz. To obtain low values of both \(e_n\) and \(i_n\) , a fully differential circuit topology combining discrete Junction Field Transistors (JFET) and Operational Amplifiers (OA) is proposed. Design equations, stability analysis, and experimental results are presented. As an example, a fully differential instrumentation amplifier has been designed, built, and tested showing \(e_n\) <1 nV/√Hz @1 kHz and \(i_n\) <10 fA/√Hz @1 kHz. The proposed topology finds applications such as front ends for measuring and testing instruments, industrial instrumentation, and audio circuits.
27 May 2024Submitted to TechRxiv
03 Jun 2024Published in TechRxiv