Metrology and Measurement Systems

Achtenberg, Krzysztof; Mikołajczyk, Janusz; Bielecki, Zbigniew

doi:10.24425/mms.2020.132785

Cited by 9 publications

References 32 publications

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A hybrid amplifier topology for low‐noise direct‐coupled front ends

Spinelli,

Haberman,

Guerrero

2024

Circuit Theory & Apps

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SummaryHybrid amplifiers combine discrete transistors with operational amplifiers (OAs) achieving superior characteristics compared with commercially available OAs, while keeping simple structures and a reduced number of parts. A single‐ended amplifier topology based on a junction field‐effect transistor (JFET) is proposed as a means of achieving very low input noise levels, both in current and voltage. It is direct‐coupled and allows to place a high‐pass filter at its input to preserve input range, or at its output to optimize noise. The proposed topology results in a low input capacitance and low input‐current noise, making it suitable for applications where multiple amplifiers are connected in parallel to achieve ultra‐low noise levels. The amplifier's gain is set by a resistor ratio, being suitable for instrumentation front ends. The circuit analysis and design equations are provided to adapt it for different applications and, as an example, an amplifier with a gain of 40 dB and a bandwidth from DC to 1 MHz was designed, built, and tested. The dominant noise contribution of the amplifier was the JFET (a JFE2140 device), featuring an input noise voltage of , that is reduced to when two amplifiers are connected in parallel.

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