A precision noise spectral density comparator

Th e theo r y is given for a prccisio n comparator t h at m eas urcs t he r atio of t wo noise s pectra l d ensit ies. The relative erro r of a single m eas urem ent is also derived. The co mp m'ator d escrib ed remo \'cs or all eviates m any of t h e probl em s i n high-sp eed s, a nd sin ce t h e in strum ent operates under null con di tio ns, the null position is cssent iall y indep ende nt of a mplifi er noise a nd gain ins tabili t ies.