How to calculate the slew rate and settling time of an opamp?

[avinash]

how to calculate the slew rate and settling time of an opamp if it is in unity gain configuration.i mean what should be the input given to positive i/p of opamp.
thanks and regards

 

[edajason]

calculate slew rate

Slew rate corresponds to the larger signal response, while setting time is in terms of small signal. Keep this in mind, you can determine the time and rate.

 

[moda]

measure slew rate

If you know the BW of your opamp, then its very simple to calculate the Slew Rate.

First calc the Rise Time from the formula:

BW=0.35/RT

For example:
BW=100MHz
SR=0.35/100MHz=3.5nsec

Now all you need to know is the voltage swing, then you will get SR.



Moda

 

[avinash]

slew rate 0.35

dear moda can you explain it again.

moreover i want to simulate and check the SR and settling time.how can i do it .

 

[Belsugului]

op amp slew rate 1.5

Slew rate is the maximum speed of changing the output signal when the input signal has changed. The slew rate most probably is given by the manufaturer's data sheet as V/us or V/ns. The settling time depends on your application, namely for a given step input how much time it takes the output to have the corresponding voltage level. Thus, the settling time can be calculated as the (slewrate) * (output voltage level required).

 

[|IAngel|]

Re: slew rate of opamp

On a simple note:

IF you designed the opamp yourself - The slewrate is approximately the current being sourced/sunk at the diff pair divided by the load capacitance. It's a rough calculation, but I've found it useful.

 

[avinash]

Re: slew rate of opamp

but how can we simulate for the SR and settling time in hspice.should i use the unity gain opamp and provide a step input at the i/p.if my supply is +2.5 to -2.5,what should be the i/p given to the unity gain opamp.what should i check at the o/p.

 

[moda]

Re: slew rate of opamp

Dear avinash,

Yes, you can simulate with a step pulse at the input, and measure the output, for my opinion you have/must simulate it in small signal, mv range and large signal V range.

That is to see if you have any instability in your system.

For settling time I think that 1-10% from the output signal will be good enough for you.

If your opamp is rail to rail output and input then you can get close to the +-vcc if not then you will lose 1-1.5v from the Vcc, that mean you will get only +-1v output voltage range.

Regards

Moda

 

[watersky]

slew rate of opamp

I ever used several steps to test sr of amp. you can use steps that change between voltages of your need. you can find this from allen's book.