In Mechanics the slew rate is given in dimensions 1 / T and is associated with the change in position of an object over time which is orbiting around the observer.

In Electronics, the slew rate is a nonlinear effect in operational amplifiers. It represents the inability of the amplifier output to keep up with rapid changes in input.

Definition

The slew-rate of an op-amp is defined as the maximum rate of change of the output voltage for all possible input signals.

Slew rate is typically expressed in units of V/μs.

Origin of slewing

There are slight differences between different op-amp designs in how the slewing phenomenon occurs. However, the general principles are the same as in this illustration.

The input stage of an op-amp is a differential amplifier with a transconductance characteristic. This means the input stage takes a differential input voltage and produces an output current into the second stage. The transconductance is typically very high - this is where the large gain of the op-amp arises. This also means that a fairly small input voltage can cause the input stage to saturate. In saturation, the stage produces a nearly constant output current.

The second stage of an op amp is, among other things, where frequency compensation is accomplished. The low pass characteristic of this stage approximates an integrator. A constant current input will therefore produce a linearly increasing output. If the second stage has an input capacitance C and gain A₂, then slew rate in this example can be expressed as:

SR = I_o1,satCA₂

where I_o1,sat is the output current of the first stage in saturation.