# Linear Integrated Circuit Questions and Answers – Thermal Drift

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Thermal Drift”.

1. Which factor affect the input offset voltage, bias current and input offset current in an op-amp
a) Change in temperature
b) Change in supply voltage
c) Change in time
d) All of the mentioned

Explanation: Any change in the mentioned parameters affect the values of input offset voltage, bias current and input offset current from remaining constant.

2. Thermal voltage drift is defined as
a) △Vio/△T
b) △VF/△T
c) △Iio/△T
d) △IB/△T

Explanation: The average rate of change of input offset voltage per unit change in temperature is called thermal voltage drift, i.e. △Vio/△T.

3. A completely compensated inverting amplifier is nulled at room temperature 25oC, determine the temperature at which the total output offset voltage will be zero?
a) 50oC
b) 25oC
c) 75oC
d) 125oC

Explanation: When amplifier is nulled at room temperature, the effect of input offset voltage and current is reduced to zero. Change in the total output offset voltage occurs only, if there is any change in the value of Vio and Iio. Therefore, the total output offset voltage will be zero at room temperature.

4. How the effect of voltage and current drift on the performance of an amplifier is determined?
a) △VooT/△T = {[1-RF/R1)]×(△Vio/△T)} + RF×(△Iio/△t)
b) △VooT/△T = {(-RF/R1)×(△Vio/△T)} + RF×(△Iio/△t)
c) △VooT/△T = {[1+(RF/R1)]×(△Vio/△T)} + RF×(△Iio/△t)
d) None of the mentioned

Explanation: As the amplifier is used in inverting configuration, the effect of voltage and current drift is given as, the average change in total output offset voltage per unit change in temperature.
△VooT/△T = {[1+(RF/R1)]×(△Vio/△T)} + RF×(△Iio/△t).

5. The error voltage in a compensating inverting amplifier is obtained by
a) Multiplying △T to total output offset voltage
b) Multiplying △T to input offset voltage
c) Multiplying △T to input offset current
d) All of the mentioned

Explanation: The maximum possible change in the total output offset voltage △VooT results from a change in temperature △t. Therefore, error voltage is obtained by multiplying △T in the average total output offset voltage.
Ev =( △VooT/△T)×△T = [1+(RF/R1)]×(△Vio/△T)×△T + RF×(△Iio/△T)×△T.
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6. A 7.5kΩ internal resistor and a 12kΩ feedback resistor are connected to an inverting amplifier. Find the error voltage, if the output voltage is 3.99mv for an input of 1.33mv.
a) ±0.6v
b) ±0.6mv
c) ± 60mv
d) ±6mv

Explanation: The output voltage of inverting amplifier is Vo= -(RF/R1)×Vin±Ev
=> Ev= ± Vo+(RF/R1)×Vin = 3.99mv+(12kΩ/7.5kΩ)×1.33mv = ±6.118 ≅ ±6mv.

7. Consider the amplifier is nulled at 27oC. Calculate the output voltage , if the input voltage is 6.21mv dc at 50oC. Assume LM307 op-amp with specification: △Vio/△T=30µV/oC ; △Iio/△T = 300pA/oC; VS =±15v. a) +0.53v or -0.68v
b) +0.52v or -0.78v
c) +0.54v or -0.90v
d) +0.51v or -0.86v

Explanation: Change in temperature △T = 50oC-27oC = 23oC.
=> Error voltage, Ev =[1+(RF/R1)]×(△Vio/△T)×△T + RF×(△Iio/△T)×△T = [1+(100kΩ/1kΩ)]×(30µv/1oC)× 23oC + 100kΩ×(300pA/1oC)× 23oC = 0.06969+ 6.9×10-9
=> Ev= 0.0704 = 70.4mv.
For an input voltage of 6.21mv dc, the output voltage,
Vo=-(RF/R1)×Vin±Ev = -(100kΩ/1kΩ)×6.21mv±70.4mv = +0.69v or -0.55v.

8. The error voltage for the above circuit is 0.93v. Compute the output voltage?
a) +15v to +17v
b) +17v or -15v
c) -17v or +15v
d) None of the mentioned

Explanation: The output voltage for the non-inverting amplifier is
Vo=[1+(RF/R1+R2)]×Vin±Ev
= [1+(50kΩ/3kΩ+10kΩ)]×3.3±0.93v = 15.99±0.93
=> Vo = +16.92v or -15.06v ≅ +17v or -15v.

Sanfoundry Global Education & Learning Series – Linear Integrated Circuits. 