ABSTRACT
As system bandwidths have increased, an accurate estimate of the noise contribution
for each element in the signal channel has become increasingly important. Many
designers are not, however, particularly comfortable with the calculations required to
predict the total noise for an op amp, or in the conversions between the different
descriptions of noise. Considerable inconsistency between manufacturers in describing
noise and, in some cases, incomplete specifications, have contributed to this confusion.
A thorough description of the op amp noise model will be developed here with a
detailed discussion of the key differences between current and voltage feedback
amplifiers. The conversions between several different measures for noise used in the
industry will also be described. Broadband effects will be covered for both low
frequencies (the 1/f region) and high frequencies (noise power bandwidth).