# Linear ICs and Applications December 2010

PART-A

1  a. What is an op-amp? Explain the working of its basic circuit.

b. Define CMRR of an op-amp. If a non-inverting amplifier is designed for a gain of 100, using an op-amp with 95 dB CMRR, calculate the common mode output (V0cm) for’a common mode input (Vicm) of 2 V.

2a.  Design a non-inverting amplifier to provide a gain of 50 for an input of 100 mV. Compute its input and output impedances. Given, Rj – 2 MQ, R<, – 75 Q, IBmax = 500 nA, and M – 200,000 for the op-amp (741).

b. How do you provide compensation for the bias current for the amplifier of Q1 (c) above?

C.  Explain the operation of a high Z-m voltage follower based AC amplifier. Prove that its Z\n is very large, ideally.

3 a. Design a C-coupled inverting amplifier for a pass-band gain of 100, fj =120 Hz and f2 = 5 kHz. Assume RL – 2 kQ and use the LF353BIFET op-amp. Explain how exactly the circuit of a non-inverting ac amplifier is modified to be used with single-supply op-amps.

b. With the help of frequency and phase response curves of a typical op-amp, discuss the concept of circuit stability for high gain and low gain amplifiers.

C. Explain the frequency compensation technique, using a phase-lead network. (04 Marks) Define the slew rate and determine the slew rate limited cut-off frequency for a 741 based voltage follower. The peak sine wave output should be 10 V. Given ; slew rate of 741 is 0.5 V/jxsec.

4 a. Explain the operation of a low resistance voltage source and design the same to provide a constant Vout of 10 V. The load varies from 100 Q to 1 KQ and the available supply is ± 15 V. Use 1N758 zener of V2 = 10V and design the various circuit elements.

b. Draw the circuit of an instrumentation amplifier and derive and expression for the gain.

c. With a circuit diagram and waveforms, explain the operation of a non-saturating precision half-wave rectifier.

PART-B

5 a. Design a V/I converter to drive a floating load of 1 KQ± 10% with a constant current of 2 mA.

b.  Explain how sustained oscillations are obtained in a Weinbridge oscillator. Draw the circuit diagram.

C. Design a RC phase-shift oscillator for a output frequency of 5 kHz. Use LM741 with ± 15V power supply.

d.  With a suitable derivation, explain a logarithmic amplifier.

6  a. Explain the operation of an op-amp based astable multivibrator. Use relevant waveforms.

b.  With waveforms, explain the working of: i) Zero-crossing detector, and

ii) Voltage-level detector.

c.   Design a 2nd order LPF using 741 for a cut-off frequency of 5 kHz. Draw its frequency response and comment on the same.

7 a. Explain the working of a series vo ltage regulator, with current limit protection.

b.   Design a 723 based voltage regulator to provide constant V0 – 20 V and Iomax =250 mA. Given Vi{1_umeg = 30V + 10%.

c.   Briefly explain the standard representation / configuration of 78XX type regulators.

8 a. Design a monostable multivibrator using 555 timer to obtain a pulse of width 10 msec.

b.   Briefly explain the working of a 4-bit binary weighted resistor DAC.

c.   Explain the operation of a successive approximation ADC using a simplified block-diagram.

d.   Define lock-in range and capture range with reference to PLLS.