A novel design technique for input differential pairs in single-ended operational amplifiers

The input differential pair (IDP) is usually a major source of nonlinear distortion in any op-amp. This is specially true if the input signal has a large common-mode component, as is the case when an op-amp functions as a unity-gain buffer, or as a single-ended sample-and-hold (S/H) circuit. The authors have already reported a novel design technique which enhances linearity of IDPs. Based on that concept they have designed and fabricated two op-amps, which differ only in their IDPs. The direct measurement results, given here, show drastic improvement in THD of up to 15 dB.