Calculate the total output offset voltage. The input offset voltage and current are 2 m V and 150 nA.

This question was previously asked in

PTCUL AE E&M 2017 Official Paper (Set B)

Option 3 : 277 mV

__Input offset voltage:__

- Whenever both the input terminals of the op-amp are grounded, ideally the output voltage must be zero. However, in this condition, the practical op-amp always shows a small non-zero output voltage.
- The input offset voltage depends upon the temperature and given as:

Vid = V1 – V2

__Input Bias current:__

- For ideal op-amp, no current flows into the input terminals but in a practical case, op-amp does have some very small input currents of the order 10-16 to 10
^{-14 }A. - Therefore input bias current is defined as the current flowing into each of the two input terminals when they are biased to the same voltage level i.e. when the op-amp is balanced.
- Input bias current is given by \({I_b} = \frac{{\left| {{I_{{b_1}}}} \right| - \left| {{I_{{b_2}}}} \right|}}{2}\)

Output offset voltage (Vo)offset due to input offset voltage is given by

\({\left( {{V_o}} \right)_{offset}} = \left[ {1 + \frac{{{R_f}}}{{{R_1}}}} \right]{V_{id}}\)

Output offset voltage (Vo)offset due to input bias current is given by:

(Vo)offset = RfIB

Rf = Feedback resistor

R1 = Input resistance of the Op-Amp

**APPLICATION:**

Voff due to input offset voltage VIo is given by \( \left( {1 + \frac{{{R_f}}}{{{R_i}}}} \right){V_{{I_o}}}\)

\(= \left( {1 + \frac{{500\;k}}{{5\;k}}} \right){V_{Io}}= \left( {1 + \frac{{500\;k}}{{5\;k}}} \right){2\ mV}=202\ mV\)

Voff due to input offset current IIo is = Rf VIo

= 500 × 103 × 150× 10-9 V

= 75 mV

Total output offset voltage due to both input offset Voltage and current is

Voff = (202 +75) mV

= **277 mV**