31. 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
Answer: A
The voltage V1 and V2 are 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.
32. 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
Answer: B
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.
33. Calculate ROM, if the value of IB1 = IB2 in the given circuit.
A. 1173.11Ω
B. 171.31Ω
C. 1171.43Ω
D. 1071.43Ω
Answer: D
Offset minimizing resistor
ROM =(R1* RF)/( R1+RF).
=> ROM = (1.2kΩ*10kΩ)/(1.2kΩ+10Ω) = 1071.43Ω.
34. 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
Answer: C
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.
35. Analyse the given circuit and determine the correct option
A. Voo ≥ VIOB
B. Voo = VIOB
C. Voo >> VIOB
D. VooIOB
Answer: C
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.
36. The specification for LM101A op-amp is given as IB =75nA. Determine the value of VIOB– V1.
A. 0.112v
B. 0.750v
C. 0.374v
D. 0.634v
Answer: A
The voltage at non-inverting terminal is given as
V1 = ROM*IB1 = 148Ω*7.5nA = 1.11µv.
=> ∵ ROM = (R1*RF)/(R1+ RF) = (15kΩ*150Ω)/(15kΩ+150Ω) =148Ω
The output offset voltage is given as VIOB = RF*IB
=> VIOB = 15kΩ*7.5nA = 112.5mv
=> ∴ VIOB– V1 = 0.112v.
37. The maximum amount by which the two input bias current may differ is known as
A. Input null current
B. Average input bias current
C. Input offset current
D. None of the mentioned
Answer: C
The maximum amount by which the two input bias current may differ is known as Input offset current.
The input offset current is defined as the algebraic difference between two input bias current.
38. A 741 type op-amp has a maximum input offset current of 200nA dc. What conclusion can be derived from this statement?
{ IB1 – Input bias current at inverting input terminal and IB2 – Input bias current at non-inverting input terminal}
A. IB1 may be larger than IB2 by 200nA
B. IB2 may be larger than IB1 by 200nA
C. Iio and IB2 may be equal to 200nA
D. All of the mentioned
Answer: D
A 741 type op-amp has a maximum input offset current of 200nA dc. The conclusion that can be derived from this statement is
IB1 may be larger than IB2 by 200nA
IB2 may be larger than IB1 by 200nA
Iio and IB2 may be equal to 200nA
In a 741 op-amp, Iio = 200nA dc, which means that the maximum difference between IB1 and IB2 can be as large as 200nA.
39. The maximum magnitude of the output offset voltage is
A. VOIio = RF*Iio
B. VOIio = RF*( IB1+IB2)
C. VOIio = RF*IB1
D. VOIio = RF*( IB1-IB2)
Answer: A
The output offset voltage due to the input offset current is given as VOIio = RF*Iio.
40. Find the output offset voltage of a 741 op-amp; If the gain of the non-inverting amplifier is 8.5 and the feedback resistor = 15kΩ? (IB=200nA for 741 op-amp)
