# VTU Old Exam Papers BE EC 4th Semester

# Linear ICs and Application July 2009

**Note: 1. Answer any FIVE full questions selecting at least TWO from each part**

**PART-A**

1 a. With a neat circuit diagramed explain basic operational amplifier circuit.

b. Explain potential divider bias for an op-amp input, with the necessary design steps.

c. i) With a neat circuit diagram, explain direct-coupled inverting amplifier.

ii) Also, design an inverting amplifier using a 741 op-amp, for which voltage gain is to be 66 and the output voltage amplitude is to be 3 V. Given : lB(max)^{=} 500 nA.

2 a. Explain the operation of a high input impedance capacitor-coupled voltage follower, with a neat circuit diagram. Obtain the expression for input impedance of the circuit.

b. Briefly discuss the upper cutoff frequency of an op-amp circuit. Show how the cutoff frequency can be set for inverting and noninverting amplifiers.

c. Design a capacitor-coupled inverting amplifier to operate with a + 20V supply. The minimum input signal level is 50mV, the voltage gain is to be 68, the load resistance is 500Q, and the lower cutoff frequency is to be 200Hz. Use 741 op-amp.

3 a. Define and briefly explain:

i) Loop gain

ii) Loop phase shift

iii) Phase margin

iv) Unity gain bandwidth.

b. With a neat circuit diagram, explain Zin Mod method of frequency compensation. Write the equation for the feedback factor.

c. Calculate the slew rate-limited cutoff frequency for a voltage follower circuit using a 741 op-amp, if the peak of sine wave output is to be 6V. Determine the maximum peak value of the sinusoidal output voltage that will allow the 741-voltage follower. Circuit to operate at the 800 kHz. Unity – gain cutoff frequency. Given : S = 0.5 v/|as.

4 a. With a neat circuit diagram, explain the operation of high input impedance full-wave precision rectifier. Draw the voltage waveforms at various points and write the appropriate equations to show that full-wave rectification is performed.

b. Design an instrumentation amplifier to have an overall voltage gain of 625. The input signal amplitude is lOmV, 741 op-amps are to be used, and the supply is ± 20V.

**PART-B**

4 a. With a neat circuit diagram and waveforms, explain the operation of

triangular/rectangular wave generator.

b. Explain working of an Wein bridge oscillator with the help of circuit diagram, waveforms and equations.

c. Using a 741 op-amp with a supply of ±15V, design a phase-shift oscillator to have an output frequency of 5.5KHz. Given : Av – 29.

6 a.With a neat circuit diagram and waveforms, explain the operation of inverting Schmitt trigger.

b. Using a 741 op-amp, design a second order high-pass filter to have a cutoff frequency of 15KHz.

(C)A capacitor-coupled zero crossing detector is to handle a 2KHz square wave with a peak-to- peak amplitude of 10V. Design a circuit using a 741 op-amp with a ±15V supply. Estimate the minimum op-amp slew rate to give a reasonably undistorted output. Also, calculate th<^ lowest sine wave input frequency that can be applied without the phase shift error exceeding 3°. Given : Vb = 0.1 V, lB(max) — 500 nA.

7 a. With a neat schematic, explain the salient features of a 723 regulator.

b. Explain the terms line regulation, load regulation and ripple rejection for a dc voltage regulator.)

c. What is the principle of switch-mode power supplies? Discuss its advantages and disadvantages.)

8 Explain the following with neat diagrams and waveforms:

a. 555 timer as a stable multivibrator

b. 566 voltage controlled oscillator

c. R-2R ladder DAC

d. Dual-slope ADC.