Write a short notes (any three) a) Schmitt trigger circuits b) BCD adders c) CMOS logic family d) Half adder

a) Schmitt Trigger Circuits:

A Schmitt trigger is a bistable multivibrator circuit that exhibits hysteresis, meaning it has two different thresholds for switching between its two states: an upper threshold for switching from the low state to the high state, and a lower threshold for switching from the high state to the low state. This hysteresis makes the Schmitt trigger circuit immune to noise and input signal variations, making it useful in applications such as signal conditioning, level detection, and pulse shaping.

The Schmitt trigger circuit consists of two cross-coupled transistors, one NPN and one PNP, along with a positive feedback loop and external resistors. The positive feedback loop creates the hysteresis by providing a regenerative effect, which amplifies the input signal and causes the circuit to switch states abruptly once the input signal reaches the threshold levels.

The upper threshold voltage (VUT) and lower threshold voltage (VLT) of a Schmitt trigger circuit can be calculated using the following equations:

VUT = VCC - VBE(Q1) - VBE(Q2)
VLT = VBE(Q1) + VBE(Q2)

where VCC is the supply voltage, VBE(Q1) and VBE(Q2) are the base-emitter voltages of transistors Q1 and Q2, respectively.

b) BCD Adders:

A BCD adder is a combinational logic circuit designed to perform addition operations on binary-coded decimal (BCD) numbers. BCD is a way of representing decimal numbers using four bits per digit, with each bit representing one of the digits 0 to 9.

A BCD adder consists of multiple stages, each stage responsible for adding two BCD digits. Each stage includes a full adder, which performs the addition of three bits (two input bits and a carry-in), and a logic circuit for handling any correction required due to the BCD representation. The correction logic ensures that the sum is represented in valid BCD format, preventing invalid digit combinations like "1001" (which would represent "11").

BCD adders are widely used in electronic calculators, digital clocks, and other devices that require arithmetic operations on decimal numbers. They offer a simple and efficient way to perform BCD addition without the need for complex conversion algorithms.

c) CMOS Logic Family:

CMOS (Complementary Metal-Oxide-Semiconductor) is a widely used logic family in digital integrated circuits (ICs). It is characterized by its low power consumption, high speed, and high noise immunity. CMOS logic circuits are constructed using complementary pairs of N-channel and P-channel MOSFETs.

In a CMOS inverter, the basic building block of CMOS logic, the N-channel and P-channel MOSFETs are connected in parallel. When the input is high, the N-channel MOSFET conducts, pulling the output low, while the P-channel MOSFET is turned off. Conversely, when the input is low, the P-channel MOSFET conducts, pulling the output high, while the N-channel MOSFET is turned off.

CMOS logic circuits offer several advantages over other logic families, including:

• Low power consumption: CMOS circuits consume significantly less power than other logic families, especially in static conditions.
• High speed: CMOS circuits can operate at high speeds, making them suitable for high-performance applications.
• High noise immunity: CMOS circuits have a high tolerance to noise and input signal variations due to their symmetrical structure.
• Scalability: CMOS technology can be easily scaled down to smaller feature sizes, enabling the development of high-density integrated circuits.

d) Half Adder:

A half adder is a combinational logic circuit that performs the addition of two binary digits (bits) and generates two outputs: a sum bit and a carry bit. The sum bit represents the result of the addition, while the carry bit indicates whether there is a carry-out from the addition.

A half adder consists of two XOR gates and an AND gate. The XOR gates are used to calculate the sum bit and the carry bit, while the AND gate is used to generate the carry-out. The truth table for a half adder is shown below:

| A | B | Sum | Carry |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 1 |

Half adders are often used as building blocks for constructing full adders, which can add three bits (two input bits and a carry-in) and generate a sum bit and a carry-out. Full adders are used in binary addition circuits, such as those found in arithmetic logic units (ALUs) of computers.