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preferred value of Rf and R1 resistances for inverting OPAMP buffer

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This question was asked by my friend's prof.:
While designing an opamp inverting buffer what must be the preferred value of Rf and R1 resistors:
Rf=R1 = 1R
OR
Rf=R1 = 1k
OR
Rf=R1 = 1M ?
 

Hi,

in detail it depends on your OPAMP, your circuit and on your specifications.

1R is not usefull,because the OPAMP may not dirve thos low impedance.

1k is most useful for standard applications.

1M you rarely need for low power and/or for high input impedance.

Klaus
 

It also depends on whether this is a voltage or current feedback amplifier. In general, a current feedback amplifier will use lower value resistors. So the real answer it depends on which type it is and what it's application is. There is no right and wrong answer although it would be unusual to see a resistor as low as 1 Ohm being used.

Brian.
 

betwixt said:
It also depends on whether this is a voltage or current feedback amplifier. In general, a current feedback amplifier will use lower value resistors.
.
Click to expand...

... however, there is a lower limit specified by the manufacturer (usually in the range of several hundreds of ohms). Feedback resistors below this limit cause instabilities.
 

The lowest value is usually determined by the maximum output current from the op amp.
The highest value is usually determined by the input bias current of the op amp (which increases output offset), and any noise considerations for low noise applications.
 

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