# Input Bias Current of Op-Amp MCQ [Free PDF] – Objective Question Answer for Input Bias Current of Op-Amp Quiz

1. Input bias current is defined as

A. Average of two input bias current
B. Summing of two input bias current
C. Difference of two input bias current
D. Product of two input bias current

Input bias current is the average of two input bias currents flowing into the non-inverting and inverting input of an op-amp.

2. Although the value of input bias current is very small, it causes

A. Output voltage
B. Input offset voltage
C. Output offset voltage
D. All of the mentioned

Even a very small value of input bias current can cause a significant output offset voltage in circuits using relatively large feedback resistors.

3. The formula for output offset voltage of an op-amp due to input bias current

A. VOIB= RF*IB
B. VOIB= (RF+R1)/IB
C. VOIB= (1+RF)*IB
D. VOIB= [1+(RF/R1)]*IB

The output offset voltage due to input bias current is VOIB = RF*IB.

4. Find the input bias current for the circuit given below

A. 10mA
B. 2mA
C. 5mA
D. None of the mentioned

Input bias current

IB=(IB1+ IB2)/2

=> IB =(4mA+6mA/2 = 5mA.

5. Mention a step to reduce the output offset voltage caused due to input bias current?

A. Use small feedback resistor and resistance at the input terminal
B. Use small feedback resistors
C. Reduce the value of load resistors
D. None of the mentioned

Since the output offset voltage is proportional to the feedback resistor and input bias current. The amount of VOIB can be reduced by reducing the value of the feedback resistor.

6. Given below is a differential amplifier in which V1=V2. What happens to VOIB at this condition?

A. VOIB= 0
B. VOIB= VOIB×10-10
C. VOIB= VOIB/2
D. VOIB= -1

The voltage Vand Vare caused by the current IB1 and IB2. Although this bias current is very small, if they are made equal, then there will be no output voltage VOIB.

7. Name the resistor that is connected in the non-inverting terminal of the op-amp which is in a parallel combination of the resistor connected in inverting terminal and feedback resistor.

A. Random minimizing resistor
B. Offset minimizing resistor
C. Offset reducing resistors
D. Output minimizing resistors

The voltage is a product of resistors and input bias current. Therefore, the value of the resistors is adjusted such that the resistors are connected at the inverting input terminal and are made equal to the resistor connected in the non-inverting input terminal.

The use of these resistors minimizes the amount of output offset voltage and therefore, they are referred to as offset minimizing resistors.

8. Calculate ROM, if the value of IB1 = IB2 in the given circuit.

A. 1173.11Ω
B. 171.31Ω
C. 1171.43Ω
D. 1071.43Ω

Offset minimizing resistor

ROM =(R1* RF)/( R1+RF).

=> ROM = (1.2kΩ*10kΩ)/(1.2kΩ+10Ω) = 1071.43Ω.

9. Calculate the output voltage for the given circuit using the specification: R1 = 820Ω; ROM=811.882Ω; Vin=10mVpp; VOIB≅0.

A. 1.025Vpp
B. 1.8Vpp
C. 1Vpp
D. 2Vpp

Offset minimizing resistor

ROM = (R1*RF)/(R1+ RF)

=> RF = (ROM* R1)/( R1– ROM)

= (812Ω*811.882Ω)/(820Ω-811.882Ω) = 82kΩ.

∴ Vo = -(RF/ R1)* Vin

= -(82kΩ/820Ω)*10mVpp = 1Vpp.

10. Analyse the given circuit and determine the correct option

A. Voo ≥ VIOB
B. Voo = VIOB
C. Voo >> VIOB
D. VooIOB

741op-amp has Vio = 6mvdc and IB =500nA.

The output offset voltage due to input offset voltage is given as

Voo =[1+(RF/R1)]*Vio

= [1+(4.7kΩ/47Ω)]*6mv = 0.606v.

The output offset voltage due to input bias current is given as

VIOB = RF*IB =4.7kΩ*500nA = 2.35mv.

=>∴ Voo >> VIOB.

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