I have come across a datasheet of an instrumentation amplifier. I have a difficulty in understanding the signal response vs settling time graphs. Can someone please explain figure 28(page 10) of the provided datasheet in the link??
The top signal shows the large signal response, and that there is a time constant of roughly 50us, the amplifier takes roughly 80us to finally settle.
I'm not sure what the bottom signal is, but I'm guessing it is the same signal but with the scope in AC coupled mode, to show the settling time in finer detail. Upon closer examination it takes 120-150us to finally settle with a large signal response. It is a little responsible to not lable the signals or put a description on the graph.
I would use this graph instead to determine the frequency response.
Settling time, as opposed to frequency response, is a very complicated issue, and is best addressed experimentally.
The problem is that, in effect, every differential amplifier has a pair of transistors, one for each input. When you first apply a difference, the two transistors heat up to different temperatures. This causes them to have different leakage currents, which produces a voltage offset which is an error term, and the time required to equalize temperatures is a major component of settling times, particularly for very small target changes such as .01%. Since the die is very small and the separation of the two transistors even smaller, equalization takes place very quickly - but in tens of microseconds rather than nanoseconds.
For high-precision, high-stability analog ICs, layout of the circuit on the die which minimizes the effects of temperature gradients is critical, and some early IC designers were lauded for their clever solutions.
Settling times to something like 1% are much, much shorter, as the thermal effects on the die are much less significant.
ETA - Oops. As laptop2d mentioned, and I forgot, settling time is measured with a step input on one input, which obviously makes a worst-case situation for the effect I've described.