Measurement of low-frequency noise of modern low-noise junction field effect transistors

A description of the low-noise measurement system designed for experimental investigation of low-frequency noise of modern low-noise junction field effect transistors (JFETs) at a frequency range from 0.5 Hz to 50 kHz is presented. The noise floor of the system in terms of noise voltage spectral density is about 1.3 nV/√Hz at frequency 0.5 Hz, 0.6 nV/√Hz at frequency 1 Hz, 0.08 nV/√Hz at frequency 10 Hz, and ≤0.04 nV/√Hz at frequencies 100 Hz-50 kHz. Such a system makes it possible to measure 1/f noise and channel thermal noise of modern very low noise n-channel JFETs. Specifically, discrete samples of JFETs, IF9030, IF1801, IF3601, and 2N4338, were investigated at the frequency range mentioned above. The system provided negligible contribution of all noise sources except intrinsic noise of measured JFETs which was a 1/f noise at frequencies f < 10 Hz and a channel thermal noise at frequencies f ≥ 10 Hz. The measured values of the equivalent input noise voltage spectral density e_n of the best samples from investigated JFETs IF9030, IF1801, IF3601, and 2N4338 were 2.7, 3.2, 3.4, and 22 nV/√Hz at frequency 0.5 Hz; 1.5, 2.1, 1.8, and 14 nV/√Hz at frequency 1 Hz; and 0.5, 0.4, 0.6, and 3.2 nV/√Hz at frequencies more than 1 kHz, correspondingly.