AC Negative Feedback OpAmp Circuits

Explain the effect that compensation capacitance has on an operational amplifier’s gain-bandwidth product (GBW). Does a larger compensation capacitance yield a greater GBW or a lesser GBW, and why?

An important AC performance parameter for operational amplifiers is slew rate. Explain what “slew rate” is, and what causes it to be less than optimal for an opamp.

It strikes some students as odd that opamps would have a constant slew rate. That is, when subjected to a step-change input voltage, an opamp’s output voltage would quickly ramp linearly over time, rather than ramp in some other way (such as the inverse exponential curve seen in RC and RL pulse circuits):

Yet, this effect has a definite cause, and it is found in the design of the opamp’s internal circuitry: the voltage multiplication stages within operational amplifier circuits often use active loading for increased voltage gain. An example of active loading may be seen in the following schematic diagram for the classic 741 opamp, where transistor Q₉ acts as an active load for transistor Q₁₀, and where transistor Q₁₃ provides an active load for transistor Q₁₇:

Explain how active loading creates the constant slew rate exhibited by operational amplifier circuits such as the 741. What factors account for the linear ramping of voltage over time?