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How do we measure slew rate of opamp in Cadence!!

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Anachip

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slew rate of op amp

Hi Guys,

I like to know, how do we measure slew rate of an opamp in cadence.

What is the relation of slew rate and settling time.

Thanks
 

slew rate cadence

Hi,

Measuring the slew rate in Cadence is similar to measuring it in other simulator. Close the feedback loop of the op-amp and apply a large step voltage to the input of the op amp, and measure the initial slope of the output.

There is not a close relation between slew rate and settling time of an op-amp. Some you can increase the slew rate of an op amp using a nonlinear circuit wile the circuit doesn’t have any effect on the settling time.

Following IEEE papers are helpful to read:

“Relationship between frequency response and settling time of operational amplifiers”
Kamath, BYT; Meyer, RG; Gray, PR.
IEEE JSSC’74

"Analysis of the settling behavior of an operational amplifier"
Chuang, C.T.;
IEEE JSSC’82
 
op amp slew rate

Hi Opamp,

Can u upload the paper you mentioned here.

Regards,
Suria
 
how to measure slew rate

OpAmp said:
Hi,

Measuring the slew rate in Cadence is similar to measuring it in other simulator. Close the feedback loop of the op-amp and apply a large step voltage to the input of the op amp, and measure the initial slope of the output.

There is not a close relation between slew rate and settling time of an op-amp. Some you can increase the slew rate of an op amp using a nonlinear circuit wile the circuit doesn’t have any effect on the settling time.

Following IEEE papers are helpful to read:

“Relationship between frequency response and settling time of operational amplifiers”
Kamath, BYT; Meyer, RG; Gray, PR.


IEEE JSSC’74

"Analysis of the settling behavior of an operational amplifier"
Chuang, C.T.;
IEEE JSSC’82
Click to expand...

hi opamp, this is the first time im measuring the slew rate in the eda tool like cadence. As you said, the opamp as close loop, now it is like a unity gain buffer. I dont get about the "large step voltage" and the slope u mentioned. Please explain me clearly.
 

measuring slew rate

run a transient analysis by giving a large voltage step at the input (rail to rail) to take the opamp in non linear mode of operation, measure the slope of the ouput waveform..that'll give you your slew rate.
 
measure slew rate

What is the relation of slew rate and settling time.
Click to expand...
Settling time is electrical parameter of opa under small signal, but the slew rate is electrical parameter of opa under large signal. I think they both have no relation.

When simulating in cadence, connect out of the opa to the inverter "-", make sure the opa is a follower. put a large pulse signal to the noninverter "+" terminal and do transient analysis, then plot the out wave(of course,under the load u defined). at last, measure the slope of out voltage linear ramp, it is slew rate.

Pls correct me if i am wrong!
 

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    Anachip

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slew rate measure

Hi guys,

Sorry for being late for your replying for questions, but, fortunately, huojinsi explained it very well. Just to add something to huojinsi, usually if we don’t use a nonlinear circuit for enhancing the SR of an opamp, a high SR opamp has also fast small signal responce. For example, when output load is small and the current in the opamp’s braches are high, the opamp has both fast small and large signal responses.

OpAmp
 

how to measure slew rate

A big thanks to Huojinsi and Opamp. i got the answer ready.
 

amp measure settling time

Make sure that you have only dc connection in the loop for biasing when you measure the slew rate. usually, you connect an Inductor in the feedback path to have a dc biasing and to exclude AC signal on this path.
 
how to measure the slew rate

dv/dt use calculator
 
cadence slew rate

good paper

any other papers about simulating op amp
 

Re: how to measure slew rate

brother plz plz plz tell me how to see slew rate of an op amp. if anyone has circuit which is working in cadence, plz give me link or upload it or mail me..
i am very week student, i hv final year project regarding slew rate enhancement.
help me
 

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