Low-noise preamplifier with input and feedback transformers for low source resistance sensors
Jacques Lepaisant, Marc Lam Chok Sing, D. Bloyet · Review of Scientific Instruments · 1992
We describe the design, schematics, and performances of a very-low-noise, low-frequency preamplifier. It operates in the 5 Hz–100 kHz range and offers an input equivalent voltage noise density as low as 65 pV/√Hz; the current noise increases with frequency and settles to about 1.5 pA/√Hz at 100 kHz. The amplifier uses input and feedback signal transformers and operates in full differential mode; a −163 dB common-mode rejection ratio is achieved at line frequency. Design methodology is applicable to other ranges of frequencies.