Nt1310 Unit 8 Lab Report

On the right in Figure 27 shown the power density spectral of noise measurements at low frequencies, from 1 Hz to 14 Hz and used commercial resistance of 1 kΩ to compare 2 different current generators. The curves in red color correspond KEITHLEY 2400 series and the curves in black color correspond to the ADRET current generator. The KEITHLEY generator slightly lower noise than ADRET generator. However, theoretically the differential measure with correct polarization can suppress this kind of noise origin from the current generator.
The result of power density spectral result from the PXI-4461 based on the scheme shown in Figure 26 without pre amplifier, S_V (f) is the sum of all component of noise in the device as following;

S_V (f)=〖S_vn〗_sp (f)+S_vn1 (t) +S_vn2 (t) +〖2 S〗_(vn1/f) (f) (IV.1.2.1)
where 〖S_vn〗_sp (f) is the signal processing, S_vn1 (t) and S_vn2 (t) are the thermal-electrical noise from nanogauge1 and nanogauge2, and 〖 S〗_(vn1/f) (f) is the flicker or 1/f noise for both nanogauges (multiplied by 2).
The thermal-electrical noise is constant in all frequencies, however at low frequencies the 1/f is dominated by the 1/f noise and by consequently, S_vn1 (t) and S_vn2 (t) are suppress from the Equation IV.1.2.1. Supposed 〖S_vn〗_sp (f), the signal noise from the PXI-4461 is negligible, and with a current source Ib with gain resistance is much less than the resistance of nanogauge ( R>>RG), the power density spectral is;
√(S_v (f) )=I_b √(2 S_(〖Rn〗_(1/f) ) (f) ) (IV.1.2.2)

and to obtain the 1/f noise from a single nanogauge, must be to divide by
√2;