op amp resistance

[jimmylovesni]

so this should be a simple question.
the gain of a op amp in inverting configuation is -rf/ri.

There are many different values of rf and ri can be used set the same gain. How does one practically pick the values.
Im assuming the ri value has to match input or output impedance of the source of the input voltage?

thanks

 

[ScottyUK]

At the bottom end of the range you need to consider the currents which will flow and the limitations of the op-amp, and obviously that the input impedance of the circuit is Ri which determines the loading on the source. At the top end of the range you need to consider the effects of bias currents which will cause offset voltages to exist. Higher resistances make this effect worse.


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If we learn from our mistakes I'm getting a great education!

 

[jimmylovesni]

thanks