Question

Find the output offset voltage of an 741 op-amp; If the gain of the non-inverting amplifier is 8.5 and feedback resistor = 15kΩ? (IB=200nA for 741 op-amp)

(a) 1µv

(b) 4 µv

(c) 3 µv

(d) 2 µv

This question was posed to me by my school teacher while I was bunking the class.

My doubt stems from Input Offset Current and Total Output Offset Voltage topic in chapter Operational Amplifier Fundamentals of Linear Integrated Circuits

Answer 1

To find the output offset voltage of a 741 op-amp in a non-inverting amplifier configuration, we can use the following relationship between the input offset current (IBI_BIB​) and the output offset voltage:

Formula:

Voffset=(IB)×Rf×GainV_{\text{offset}} = (I_B) \times R_f \times \text{Gain}Voffset​=(IB​)×Rf​×Gain

Where:

• IBI_BIB​ is the input bias current (given as 200 nA for the 741 op-amp),
• RfR_fRf​ is the feedback resistor (given as 15kΩ),
• Gain is the gain of the amplifier (given as 8.5).

Step-by-Step Calculation:

1. Input Bias Current: IB=200 nA=200×10−9 AI_B = 200 \, \text{nA} = 200 \times 10^{-9} \, \text{A}IB​=200nA=200×10−9A
2. Feedback Resistor: Rf=15 kΩ=15×103 ΩR_f = 15 \, \text{kΩ} = 15 \times 10^3 \, \text{Ω}Rf​=15kΩ=15×103Ω
3. Amplifier Gain: $\text{Gain}=8.5$

Now, we substitute these values into the formula:

Voffset=(200×10−9)×(15×103)×8.5V_{\text{offset}} = (200 \times 10^{-9}) \times (15 \times 10^3) \times 8.5Voffset​=(200×10−9)×(15×103)×8.5 Voffset=200×10−9×15×103×8.5V_{\text{offset}} = 200 \times 10^{-9} \times 15 \times 10^3 \times 8.5Voffset​=200×10−9×15×103×8.5 Voffset=2550×10−6 V=2.55 μVV_{\text{offset}} = 2550 \times 10^{-6} \, \text{V} = 2.55 \, \mu \text{V}Voffset​=2550×10−6V=2.55μV

The output offset voltage is approximately 2.55 µV.

Closest Answer:

The closest available answer to 2.55 µV is:

(d) 2 µV

So, the correct choice is (d) 2 µV.