# Linear Integrated Circuit Questions and Answers – Very High Input Impedance Circuit

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Very High Input Impedance Circuit”.

1. Which among the following circuit has the highest input resistance?
a) Voltage follower
b) Inverting amplifier
c) Differential amplifier
d) None of the mentioned

Explanation: Voltage follower has the highest positive input resistance of any op-amp circuit. For this reason it is used to reduce voltage error caused by source loading.

2. Find the bias current from the given circuit a) 30mA
b) 3mA
c) 0.30mA
d) 0.03mA

Explanation: The bias current is given as Iin =Vin/Rin = 3v/10kΩ.
Where, Iin= Ib =0.3mA.

3. How to choose an op-amp when working with high input source resistance?
a) Op-amp with low bias current
b) Op-amp with higher slew rate
c) Buffer or voltage follower
d) All of the mentioned

Explanation: When the op-amp is driven by a high input source resistance, the output and input voltage will not be equal due to error at the input. A remedy to this problem is an op-amp with low input bias current and high slew rate should be chosen as a voltage follower.

4. What must be done to block the ac input voltage riding on a dc level?
a) Use RC network
b) Use coupling capacitor
c) Use resistive transducer
d) None of the mentioned

Explanation: In order to block the dc level a coupling capacitor must be used in series with the input of the voltage follower.

5. To get higher input resistance in AC coupled voltage follower,
a) The output resistance is bootstrapped
b) The input resistance is bootstrapped
c) The bias resistance is bootstrapped
d) The feedback resistance is bootstrapped

Explanation: Bias resistor connected to ground to provide path in an AC coupled voltage follower, drastically reduces the input resistance of the circuit. Therefore, to get high input resistance, the bias resistance is bootstrapped.

6. Find out AC-coupled voltage follower?
a) b) c) d) None of the mentioned

Explanation: An AC coupled voltage follower consists of coupling capacitor at the input of non-inverting terminal.

7. Voltage follower circuit are used in
a) Active filter
b) All of the mentioned
c) Sample and hold circuit
d) Bridge circuit with transducer

Explanation: Voltage followers are useful for all the above mentioned applications, because they involve working with high-input source resistance.

8. Compute the reference voltage for a fundamental log-amp, if it’s internal resistance=5MΩ.
a) 0.5µv
b) 0.05µv
c) 5µv
d) None of the mentioned

Explanation: Reference voltage, Vref = R1 × Is
Where, Is~10-13A (for an emitter saturation current).
∴ Vref = 10-13 × 5MΩ = 5×10-7 = 0.5µv.

Sanfoundry Global Education & Learning Series – Linear Integrated Circuits. 