Jun 30 2011
Opamp Psrr
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Opamp Psrr
How do i know the change in voltage supply for LM107 and LF411 OpAmp?
Basing from the datasheet of LM107:
http://cache.national.com/ds/LM/LM107.pdf
and of LF411: http://www.national.com/ds/LF/LF411.pdf
For the case of LF411
The PSRR or the Supply Voltage Rejection Ratio is 70dB (minimum value).
20log(1 / PSRR) = 70dB
1 / PSRR = 10 ^ (70/20)
PSRR = 316.227766uV / V
Computing the ∆Voo due to voltage supply variation ∆Vsupp,
∆Voo = (1 + Rf/Ri) * (∆Vio / ∆Vsupp) * (∆Vsupp)
∆Voo = (2.0) * (316.227766uV / V) * (∆Vsupp)
∆Voo = ___
I couldnt have the ∆Voo since i dont know (∆Vsupp). Also what should be the supply voltage? is 20V okay? what should be my basis?
The lower the ∆Voo, the better right???
Please help me all. THANK YOU AGAIN!!!!!!
*bows*
You are trying to calculate the power supply sensitivity. So it depends on the power supply, not the op amp. So get the data sheet for whatever regulator you are using, and see how much voltage fluctuation you get over the operating temperature range. A supply of +15V +- 0.1V would be reasonable.
Usually you get a lot more drift from the input offset voltage than from power supply sensitivity. So just assume +-0.1V, and if the other sources of drift are a lot larger, then you can neglect this particular source of drift. I have been designing amplifiers for 30years, and have never had to worry about power supply fluctuations even one time.
To decide on your power supply voltage, first see how much output voltage you need. Then add enough "overhead" to keep the op amp happy. The required overhead comes from the op amp data sheet.
You need to actually build and test a few op amp circuits to get the hang of this - you can't do it from data sheets only because the data sheets do not give you a feel for the practicalities of the situation.
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