Why do data sheets sometimes define short term and long term settling characteristics?
A. The traditional definition of settling time is the time from the input transition to the time when the amplifier output enters the specified error zone and does not leave again. This concept is relatively uncomplicated and straightforward. However, there are some cases where the initial settling is fast, followed by an extended period of settling to the final value. Single-supply amplifiers may exhibit this characteristic in the vicinity of the lower rail. Of greater prevalence for large transients, a “thermal tail” is a slow drift that continues for a relatively long time after rapid settling to apparently excellent initial accuracy. Thermal tails are produced when voltage level changes within the op amp caused by a step transition create temperature gradients among the transistors. Matched transistors will not track well while they are at temporarily different temperatures. The thermal time constant of the chip determines how long it takes for equilibrium to return. Op amps are de
