FET input voltage amplifier for low frequency noise measurements

Abstract

The paper presents a low noise voltage FET amplifier for low frequency noise measurements. It was built using two stages of an op amp transimpedance amplifier. To reduce voltage noise, eight-paralleled low noise discrete JFETs were used in the first stage. The designed amplifier was then compared to commercial ones. Its measured value of voltage noise spectral density is around 24 nV/√ Hz, 3 nV/√ Hz, 0.95 nV/√Hz and 0.6 nV/√ Hz at the frequency of 0.1, 1, 10 and 100 Hz, respectively. A −3 dB frequency response is from ∼ 20 mHz to ∼ 600 kHz.