Fully Differential Operational Amplifiers

As the supply and signal voltages go down to lower values from 30, 12, 5, 3, 2, and finally 1 V, the signal-to-noise-and-interference ratio becomes increasingly worse. An important way to cope with this problem is to use fully differential signal paths. The differential peak-to-peak signal then becomes maximally twice the total supply voltage V S = V SP − V SN . But even more important will be that the influence of substrate interference on the two balanced signals will largely cancel one another. All kinds of amplifiers, filters, sigma-delta converters, and other circuits using fully differential OpAmps may thus be designed in a fully balanced or differential way. In this chapter several practical design examples of fully differential operational amplifiers are presented.