Opamp slew rate measurment

hi
I've read somewhere that for measurement of slew-rate of an op-amp with simulation, we place the op-amp in negative feedback structure and for a square wave as input signal, the transient slope from 10% to 90% of output is regarded as slew-rate.
question 1: considering a supply voltage as VDD, and considering that the input swing and output swing of op-amp are different and considering that slew-rate is a small quantity,in below picture how must we determine the amplitude of VPULSE, namely whats it's value and from which value to which value?

question 2: in a two stage amplifier as below picture, with considering slew-rate definition namely slew-rate=I/C , how can we use this to calculate slew rate and how is calculated nagative and positive slew-rate?

thanks.

1, time should be much smaller than expected slewing, smallest as possible, however too small can cause convergence errors in the simulation. So if you expect a rising time for example 1us from 10% to 90% then if you use 1000 times smaller rising time, which is 1ns then it will be good for the simulator and won't cause high error in the measurement.

From/To values depend on the input common mode voltage range, and on the ouput headroom, you shouldn't go further than any of these limits. And if you want to get worst case rising time (very practical) you should use the highest available range, not small steps.

2, Google is your friend, see page 6. **broken link removed**

Hi,

I've read somewhere

Click to expand...

Instead of "somewhere" I recommend to look for such informations at the OPAMP manufacturers. They write the specifications and they can tell how to verify those specifications.

Also many OPAMP datasheets provide information about the test circuit and the test conditions.

Klaus

Added:
There are many test conditions. Inverting or non inverting, Gain of 1 or gain of 5, input extremely fast or also slew rate limited...

A limited input slew rate may have benefits. It may prevent the input stage from saturation and thus can vary the SR result and the delay result.

Slew rate depends a lot on inut overdrive, an A=100 setup
that only lets you impose 50mV will be a fair bit different
than an A=1 setup and smacking the front end with an
abrupt 5V of overdrive. How completely steered the input
pair is, determines a lot.

And you would like to test it how you apply it, not in the
way that lets the manufacturer brag the most.