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Slew Rate for a Differential Amplifier (Read 97 times)
kanishxmas
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Slew Rate for a Differential Amplifier
Feb 12th, 2018, 9:34pm
 
Hello All,

I am wondering if you can suggest a test bench that will allow me to measure the slew rate of a differential amplifier with CMFB?

Thanks! Smiley Cheesy

-K
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Tako
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Re: Slew Rate for a Differential Amplifier
Reply #1 - Feb 13th, 2018, 2:40am
 
Wouldn't it be the case as proposed here (https://payhip.com/b/5Srt - the picture is in the paid version. For other stuff press Preview button) in Fig. 1.21 in chapter "1.4. Slew-rate": see the attached picture?



But in your case you just ramp two inputs in the opposite directions.

Sorry, for the proposed position, but I had it at hand. If the need is, for sure I will be able to find you something free and also in the differential configuration. Just write in case more explanations are necessary and if I have time I will try to look for it.
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slewrate2.png
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kanishxmas
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Re: Slew Rate for a Differential Amplifier
Reply #2 - Feb 13th, 2018, 7:57pm
 
Hello,

Thanks for the reply. I was reading online I could calculate the slew rate as you mentioned, by putting pulse inputs. I also found a test bench I may be able to use. My question is, what value of R seems appropriate on this test bench (10K?)? How do I measure the slew rate "output"? Is it with the calculator on the graph, (Vout+) - (Vout-)?

Thanks.
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Tako
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Re: Slew Rate for a Differential Amplifier
Reply #3 - Feb 14th, 2018, 9:37am
 
You should use resistors that you are using in your application. Your differential amplifier will work in a specific configuration, for example with the feedback path as you draw, is that right? If so, just use these value of resistors. As a results you will have a real value of slew-rate. Not the case where you have one value of SR in a SR testbench and another one in TOP simulation or somewhere else.

Resistors in the feedback paths would rather not affect SR value so much unless they have low value comparing to the current possibilities you have at the output.

You measure SR as you wrote. Using calculator. Remember as written here in a paid version https://payhip.com/b/5Srt, but also other books or in the internet that you have different SR values for rising and falling slopes. Depends on the opamp architecture.
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