How to get constant values of the Rin?

[lucky8]

Rin

Guyz,

i'm trying to measure the input resistance, Rin.
Basically, Rin = Vio/Iio (ohms law). unfortunately, the values that i get is non-constant. it varies from 0.002Mohm ~ hundreds Mohms.
so, is there anyway to get a constant values?

tq

 

[sunking]

Rin

for high impedence input device, it is difficult to get a constant values.
normally, it is have a min value

 

[lucky8]

Re: Rin

Sunking,

May i know the min value for the Rin or the typical value for Rin. the op amp is the general purpose op amp.

 

[ignosi]

Re: Rin

So Rin is not constant

 

[lucky8]

Re: Rin

Does the non-constant Rin values affected by the doping or anything during the fabrication?