Slew rate Vs GBW of opamp Confusion..

Hello Friends

I was studying for the OPAMP Basics.

I understand the Gain bandwidth Product as well.

When i reached to the Slew rate..
Slew rate=V/uS...

They specified out the There for the max operating frequency

Fmax=Slew rate/(2*pi*VPEAK)

Where as slew rate=v/uS=F*V

Now which criteria should take into considerations while designing..

Or both are the same

Marx

Hi,

The lower value of both.

Because the slew_rate_limit depends on magnitude of output signal:
* usually with small output signal...GBW is the limit
* usually with small output signal...slew_rate is the limit

For sure it also depends on signal waveform.
* because of the slew rate limit you can never reproduce a perfect square wave signal
* a triangle waveform is better to reproduce
* a sine is even better

Klaus

Also
i would like to understand the term.

db/octave..

it was showing in the graph that Falls off 6db/octave..

What exactly it means..
Graph is Gain vs Frequency..

Hi,

it falls 6db/octave means:
* falls = minus

* minus 6db = -6dB = 10 ^(-6/20) = 0.5 (as factor) = 50%

* one octave (like in music) is doube (or half) the frequency.

Now the formula 6db/octave means: with double the frequency you get half of the amplitude.
This is the behaviour of an integrator, or the behaviour of a first order low_pass_filter in stop band.

Example:

let´s say the amplitude at 440Hz is 1V (music: standard "A")
Then at double the frequency it is half the amplitude: 880Hz --> half of 1V = 0.5V (the next higher "A")
and further 1760Hz --> half of 0.5V = 0.25V (again the next higher "A")
and so on.

In general: multiply the frequency with x, then you get 1/x of the amplitude. (= you have to divide the amplitude by x)

Added: indeed 6dB is not exact: it should be -6.0206... but to ease this we simply say 6dB.

Klaus