DC Imperfections
Wednesday, 10 July 2019
7:29 PM
Consider an inverting amplifier where there is no input into either terminals
Ideally, would be zero, but this is not the case in real life.
There are DC imperfections within the op-amp which cause to be non-zero
The transistors within the op-amp draw some current - known as the input bias current ( and )
The mismatch of the transistors for the non-inverting and inverting terminals cause
The input offset current
There is also an input offset voltage, where the non-inverting and inverting terminals have different potentials
BJT | Base-Emitter Voltage
MOSFET | Gate-Source voltage
We need to consider the three causes of DC imperfection: input bias current, input offset current, and input offset voltage
We can calculate the maximum (worst case) output voltage offset with
So, then
Apply superposition
To calculate , disable and and apply golden rules
To calculate , disable and and apply golden rules
To calculate , disable and and apply golden rules
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