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- Title
A hybrid amplifier topology for low‐noise direct‐coupled front ends.
- Authors
Spinelli, Enrique M.; Haberman, Marcelo A.; Guerrero, Federico N.
- Abstract
Summary: Hybrid 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 0.95nV/Hz@1kHz, that is reduced to 0.70nV/Hz@1kHz when two amplifiers are connected in parallel.
- Subjects
TRANSISTORS; JUNCTION transistors; OPERATIONAL amplifiers; NOISE; ELECTRIC capacity
- Publication
International Journal of Circuit Theory & Applications, 2024, Vol 52, Issue 9, p4783
- ISSN
0098-9886
- Publication type
Article
- DOI
10.1002/cta.3989