(SEM V) THEORY EXAMINATION 2019-20 INTEGRATED CIRCUITS

INTEGRATED CIRCUITS (REC-501A)

B.Tech (SEM-V) – AKTU

SECTION A

(Attempt all questions – 2 × 7 = 14 marks)

Q1 (a) What is a Current Mirror circuit? Give its need.

A current mirror is a circuit that copies a reference current and produces an output current that is equal or proportional to it. It is widely used in ICs to provide constant current sources, biasing of amplifiers, and active loads. The need for current mirrors arises because resistors occupy large chip area and are not accurate in IC fabrication.

Q1 (b) What do you mean by DC analysis of a circuit?

DC analysis of a circuit involves determining the operating point or quiescent point of active devices by considering only DC sources. Capacitors are treated as open circuits and inductors as short circuits during DC analysis.

Q1 (c) Describe the need of voltage limiter circuits.

Voltage limiter circuits are used to protect electronic components from excessive voltage levels. They prevent output signals from exceeding a specified limit and are commonly used in signal conditioning and protection circuits.

Q1 (d) Differentiate wideband and narrowband pass filters.

Wideband pass filters allow a large range of frequencies to pass and are used in audio and communication systems. Narrowband pass filters allow only a small frequency range and are used in tuned amplifiers and radio receivers.

Q1 (e) Draw the basic structure of CMOS inverter.

A CMOS inverter consists of a PMOS transistor connected to VDD and an NMOS transistor connected to ground. Both gates are connected together as input, and the output is taken from the junction of the two transistors. It provides low power consumption and high noise margin.

Q1 (f) Differentiate between Comparator and Schmitt Trigger.

A comparator compares two input voltages and gives a high or low output based on which input is greater. A Schmitt Trigger is a comparator with hysteresis, meaning it has two different threshold voltages to reduce noise sensitivity.

Q1 (g) The basic step of an 8-bit DAC is 20 mV. If 00000000 represents 0 V, what is represented by input 10110111?

Binary number 10110111 = 183 (decimal).
Output voltage = 183 × 20 mV = 3.66 V

SECTION B

(Attempt any three – 7 × 3 = 21 marks)

Q2 (a) Find the overall gain of op-amp IC 741 using its cascaded stages. Also derive relation between ft and slew rate.

The IC 741 consists of input differential amplifier, intermediate gain stage, and output stage. The overall gain is the product of gains of individual stages.
The gain-bandwidth product relates unity gain frequency ft with closed-loop gain. Slew rate defines the maximum rate of change of output voltage and limits high-frequency performance.

Q2 (b) Draw generalized impedance converter and derive its impedance equation. Also simulate an inductor.

A generalized impedance converter (GIC) uses two op-amps and five impedances to simulate inductance using resistors and capacitors. The equivalent impedance can be derived using circuit analysis. By choosing proper components, an inductive behavior is obtained without using physical inductors.

Q2 (c) Discuss the features of CMOS circuits. Realize one AOI and one OAI logic gate.

CMOS circuits offer low power consumption, high noise immunity, and high packing density.
An AND-OR-INVERT (AOI) gate performs AND operation followed by OR and inversion.
An OR-AND-INVERT (OAI) gate performs OR operation followed by AND and inversion. These gates reduce transistor count and improve speed.

SECTION C

(Attempt any one part from each unit – 7 × 2 = 14 marks)

Q5 (a) Realize 2-input NOR and 2-input NAND gates using CMOS and explain operation.

A 2-input NOR gate uses parallel PMOS transistors and series NMOS transistors. The output is high only when both inputs are low.
A 2-input NAND gate uses series PMOS transistors and parallel NMOS transistors. The output is low only when both inputs are high.

Q6 (a) What do you mean by quadrant operation of multiplier? Draw and explain Gilbert cell multiplier.

Quadrant operation refers to multiplication of signals with positive and negative polarities.
The Gilbert cell is a four-quadrant analog multiplier using differential pairs. It provides accurate multiplication and is widely used in mixers and modulators.

Q7 (a) Explain block diagram of IC 555 and derive time delay for monostable multivibrator.

IC 555 consists of comparators, flip-flop, discharge transistor, and voltage divider.
In monostable mode, the output pulse width is given by
T = 1.1 RC
where R is resistance and C is capacitance.