# Digital Electronics

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Digital electronics notes, lectures for engineering and diploma students

## Magnetic Bubble Memories

Magnetic bubble memories use small magnetized areas, called bubbles to represent data bits. An alternating electric field causes the bubbles to shift down the register

## SEMICONDUCTOR MEMORY

The main requirements of semiconductor memories are that they occupy a small area, have a fast access time and operate with low power consumption. In addition they are non-volatile.

## MEMORIES

The memory unit in a digital computer performs the storage function. It must provide means of access for the retrieval or readout, and alteration or write-in, of selected portions of the stored information

## CHOPPER AMPLIFIER

Let us assume that we are required to amplify a small signal say of the order of millivolt and that the signal v(t) is one in which change in volt with respect to time i.e. dv/dt is very small

## De Morgan's Theorem

De Morgan's theorem stats that "The complement of the sum of two or more variables is equal to the product of the complement of the variables."

## BOOLEAN ALGEBRA

Boolean algebra permits only two values or states for a variable. In logic, these two states represent 'true' and 'false' and in circuits they represent 'on' and 'off' or the 'cutoff' and 'saturation' state of Boolean of an electronic device.

## DELAY LINES

In many pulse circuit applications, it is necessary to delay a signal ba a certain amount of time called delay time.

## Bistable Multivibrator

The bistable multivibrator has two absolutely stable states. It will remain in whichever state it happens to be until a trigger pulse causes it to switch to the other state.

## ASTABLE MULTIVIBRATOR

A multivibrator which generates square waves of its own (i.e without any external trigger pulse) is known as astable multivibrator. It is also called free ramming multivibrator. It has no stable state but only two quasi-stable (half-stable) makes oscillating continuosly between these states.

## Monostable Multivibrators

In a monostable multivibrator, one of the state is absolutely permanent i.e, stable and the other one is temporary i.e, quasi-stable. collector coupled,emitter coupled, OP-AMP, and 555 timer IC Monostable multivibrators

## LC feedback Oscillator

These are resonant circuit or tank circuit oscillators. They are commonly use to produced high frequencies as ranging from I MHz to 500 MHz Hence they are also known as RF oscillators

## RC FEEDBACK OSCILLATORS

RC oscillators employ resistors and capacitors and are used to generate low or audio-frequency signals. Hence they are also known as audio-frequency (A.F) oscillators.

## Oscillators

An oscillator is an electronic device for generating an AC signal voltage. Oscillators generate sinusoidal or non-sinusoidal waveform from very low frequencies up to very high frequencies.

## 555 timer IC as a-stable Multivibrator

A 555 timer IC is used a a-stable multivibrator as shown in the given figure (A). The threshold input is now connected to the trigger input (Pin 2), the resister R1, R2 and capacitor C1 for timing network which set the frequency of the oscillator.

## CLAMPING CIRCUITS

Certain applications in electronics require that the upper or lower extremity of a wave be fixed at a specific value In such applications ,a clamping/clamper circuits are  used.