Linear Integrated Circuit Questions and Answers – Square Wave Generator

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “Square Wave Generator”.

1. How are the square wave output generated in op-amp?
a) Op-amp is forced to operate in the positive saturation region
b) Op-amp is forced to operate in the negative saturation region
c) Op-amp is forced to operate between positive and negative saturation region
d) None of the mentioned
View Answer

Answer: c
Explanation: Square wave outputs are generated where the op-amp is forced to operate in saturated region, that is, the output of the op-amp is forced to swing repetitively between positive saturation, +Vsat and negative saturation, -Vsat.

2. The following circuit represents a square wave generator. Determine its output voltage
Determine the output voltage from the circuit which represents a square wave generator
a) -13 v
b) +13 v
c) ± 13 v
d) None of the mentioned
View Answer

Answer: a
Explanation: The differential output voltage Vid = Vin1 – Vin2= 3-7v = -4v.
The output of the op-amp in this circuit depends on polarity of differential voltage V0= -Vsat ≅ -Vee = -13 v.

3. Determine the expression for time period of a square wave generator
a) T= 2RC ln×[( R1+ R2) / ( R2)].
b) T= 2RC ln×[( 2R1+ R2) / ( R2)].
c) T= 2RC ln×[( R1+ 2R2) / ( R2)].
d) T= 2RC ln×[( R1+ R2) / (2 R2)].
View Answer

Answer: b
Explanation: The time period of the output waveform for a square wave generator is T= 2RC ln×[(2R1+ R2)/( R2)].
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4. Determine capacitor voltage waveform for the circuit
Determine capacitor voltage waveform for the circuit
a)
Find the negative saturation from the given diagram
b)
Find the positive saturation from the given diagram
c)
Find the time period of the output waveform from the given diagram
d)
Find the square wave generator from the given diagram
View Answer

Answer: c
Explanation: When the op-amp output voltage is at negative saturation, V1 = [(R1) / (R1+ R2 )] × (-Vsat) = [10kΩ / ( 10 kΩ +11.6 kΩ)] × (-15v) = -7v.
Similarly, when the op-amp’s output voltage is at positive saturation, V1 = [(R1) / (R1+ R2 )] × (+Vsat) = [10kΩ/ ( 10 kΩ +11.6 kΩ)] × (+15v) = +7v
The time period of the output waveform,T= 2RC ln ×[( 2R1+ R2) / ( R2)] = 2× 10kΩ × 0.05 µF× ln (2×10kΩ + 11.6kΩ) / 11.6kΩ] = 1×10-3 × ln2.724 = 1ms.
The voltage across the capacitor will be a triangular wave form.

5. What will be the frequency of output waveform of a square wave generator if R2 = 1.16 R1?
a) fo = (1/2RC)
b) fo = (ln/2RC)
c) fo = (ln /2 ×√RC)
d) fo = (ln/√(2 RC))
View Answer

Answer: b
Explanation: When R2= 1.16 R1, then fo = 1/2RC× ln[ (2R1+ R2) / R2] = 1/2RC ×ln [(2R1 + 1.161R1 )/ (1.161R1)] = 1/( 2RC×ln2.700)= 1/2RC.
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6. What could be the possible output waveform for a free running multivibrator whose op-amp has a supply voltage of ±5v operating at 5khz?
a)
Find the supply voltage of ±5v operating from the given diagram
b)
Find the differential current flow from the given diagram
c)
Free running multivibrator b/w positive & negative saturation to produce square wave output
d) None of the mentioned
View Answer

Answer: c
Explanation: In a free running multivibrator, the output is forced to swing repetitively between positive and negative saturation to produce square wave output. Therefore, +Vsat ≅ +Vcc =+5v and -Vsat ≅ -Vcc =-5v.
=> Frequency= 5khz , f =1/t = 0.2ms.

7. Determine the output frequency for the circuit given below
Determine the output frequency for the given circuit
a) 28.77 Hz
b) 31.97 Hz
c) 35.52 Hz
d) 39.47 Hz
View Answer

Answer: d
Explanation: The output frequency fo = 1/2RC×ln [ (2R1+ R2)/ R2] = 1 / {(2×33kΩ ×0.33µF)×ln[(2×33kΩ +30kΩ)/30kΩ]} = 1/ (0.02175×ln 32) = 39.47 Hz.
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8. The value of series resistance in the square wave generator should be 100kΩ or higher in order to
a) Prevent excessive differential current flow
b) Increase resistivity of the circuit
c) Reduce output offset voltage
d) All of the mentioned
View Answer

Answer: a
Explanation: In practice, each inverting and non-inverting terminal needs a series resistance to prevent excessive differential current flow because the inputs of the op-amp are subjected to large differential voltages.

9. Why zener diode is used at the output terminal of square wave generator?
a) To reduce both output and capacitor voltage swing
b) To reduce output voltage swing
c) To reduce input voltage swing
d) To reduce capacitor voltage swing
View Answer

Answer: b
Explanation: A reduced peak-peak output voltage swing can be obtained in the square wave generator by using back to back zener diodes at the output terminal.
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10. A square wave oscillator has fo =1khz. Assume the resistor value to be 10kΩ and find the capacitor value?
a) 3.9 µF
b) 0.3 µF
c) 2 µF
d) 0.05µF
View Answer

Answer: d
Explanation: Let’s take R2 = 1.16 R2, therefore the output frequency fo = 1/2RC
=> C = 1/2Rfo = 1/ (2×10kΩ×1khz) = 0.05µF.

Sanfoundry Global Education & Learning Series – Linear Integrated Circuits.

To practice all areas of Linear Integrated Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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