What is the slew rate and Gain-Bandwidth product ?

slew rate op amp

Can someone explain to me in a little more detail what the slew rate and Gain-Bandwidth product is, in regard to op-amps?

op amp slew rate gain bandwidth

Slew rate is basically how fast an opamp can swing its output. It turns out that when you apply a very fast large-signal transient (like a step voltage) the opamp can't "keep up". The limiting factor is often an internal capacitance that is charged by a constant current (when we turn a differential pair completely on, it acts like a constant current, and the internal capacitance is often the compensation capacitor). The rate of change is dV/dT = I/C, where I is the constant current, and C is the capacitance. On the scope, if you apply a large step input, you will see the output changing linearly at first, then taking on a "RC" type waveform. The linear portion is the op-amp slewing (and the slew rate is the slope of that line).

You can read a lot more about it in any number of books: grey & meyer, razavi, horrowitz & hill, sedra & smith, etc...

The gain bandwidth concept works like this: your average opamp has a specification for DC gain (Av0), and also for unity-gain bandwith. Unity-gain bandwidth is the 3dB bandwidth of the opamp when configured with a gain of 1. If you work through a couple bode plot problems, you will see how bandwidth and gain trade off. It turns out that if you multiply the gain by the bandwidth, it's approximately constant. So the unity-gain bandwidth * DC gain = gain bandwidth product (GBW). Now if we want to operate at a lower gain (say, 10), we can make a good guess as to the bandwidth of the resulting system by simply dividing the GBW by our desired gain -- 10. This is another topic that should be treated by any of the basic texts.

Hope this helps!

slew rate: op-amps

for slew rate ,plz refer