Question:
Here is the given solution:
Now, the datasheet gives:
Maximum offset voltage: 30mV
Maximum input bias current: 60pA
Maximum input offset current: 30pA
I calculated the offset at Vout due to the offset voltage as 30mV the same as what the solutions give.
I am a little confused about the offset voltage at Vout due to the input bias current however. I do not understand why he multiplied Ios_ by the parallel combination of the resistances.
What I did was:
Since the + terminal is grounded (superposition rule), we have a virtual ground at the node between the two resistors and since current cannot go into the opamp (golden rule).
(Vout - 0)/450k + Ib- = 0
Vout/450k = -Ib-
Therefore Vout = -27uV due to the maximum bias current
Whereas they seemed to use the total parallel resistance and get 2.7uV
Please explain?
Here is the given solution:
Now, the datasheet gives:
Maximum offset voltage: 30mV
Maximum input bias current: 60pA
Maximum input offset current: 30pA
I calculated the offset at Vout due to the offset voltage as 30mV the same as what the solutions give.
I am a little confused about the offset voltage at Vout due to the input bias current however. I do not understand why he multiplied Ios_ by the parallel combination of the resistances.
What I did was:
Since the + terminal is grounded (superposition rule), we have a virtual ground at the node between the two resistors and since current cannot go into the opamp (golden rule).
(Vout - 0)/450k + Ib- = 0
Vout/450k = -Ib-
Therefore Vout = -27uV due to the maximum bias current
Whereas they seemed to use the total parallel resistance and get 2.7uV
Please explain?