The unfiltered 1-kHz reference sign is utilized to the INA noninverting enter, whereas the identical sign is utilized to the DUT, whose output is related to the remaining INA enter. As a result of the instrumentation amplifier possesses good common-mode rejection at 1 kHz (sometimes >80 dB), the distortion elements widespread to the supply and the DUT output are attenuated accordingly.
As a result of a lot of the sign amplitude at 1 kHz is eliminated, the remaining distinction sign, due solely to the DUT, can now be gained as wanted (generally about 40 dB) and output to the spectrum analyzer. This raises the sign above the system’s noise flooring by the INA acquire of 40 dB.
Decision can also be enhanced by the identical 40-dB acquire. Furthermore, the outcomes aren’t affected by the reference sine-wave purity, as supply distortion elements are widespread to each inputs and rejected by the INA. On high of that, no filters are wanted.
This text was initially printed on June 21, 2004.
