25-08-2017, 09:32 PM

LINEAR WAVESHAPING

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Introduction:

If a circuit is designed with components like R ,L and C then it is called linear circuit.

When sinusoidal signal is applied ,the shape of the signal is preserved at the output with

or without change in the amplitude and shape. But a non-sinusoidal signal alters the

output when it is transmitted through a linear circuit.

The process whereby the form of non-sinusoidal signals such as step, pulse,

square wave, ramp and exponential is altered by transmission through a linear network

is called linear wave shaping.

HIGHPASS RC CIRCUIT

Consider high pass RC circuit as shown in fig.1 below.

The capacitor offers high reactance at low frequency and low reactance at high

frequency. Hence low frequency components are not transmitted ,but high frequencies are with

less attenuation. Therefore the output is large and the circuit is called a high pass circuit.

Let us see now is, what will be the response if different types of inputs, such as,

sinusoidal ,step, pulse, square wave, exponential and ramp are applied to a highpass circuit., like?

MULTIVIBRATORS

Multivibrators are cross-coupled two-stage regenerative amplifiers acting as switching

circuits . Multivibrators are broadly classified as

1. Bistable multi or binary or Flip-Flop

2. Monostable multi or One shot multi or univibrator

3. Astble multi or Freerunning multi

Multivibrators are extensively used in digital and switching applications. A bistable

multivibrator remains in one of the stable states until we are asked to change. Hence this

circuit is essentially used as a memory element in digital circuits..

A monostable multi has only one stable state and one quasi-stable state. Initially the multi

is in stable state. After the application of a trigger, the multi goes into the quasistable

state and stays there for a finite time and will return back to the initial stable state. Such a

circuit is used as a gate.

Other type of multivibrator is an Astable multi which has two quasistable states. This

means that change of state occurs in the multi simultaneously. So, the output of this multi

is a squarewave. The output of an astable multi is normally used as a clock signal in

digital circuits.

Methods of triggering a binary:

To change the binary from one stable state to the other, a pulse of short duration

with sufficient amplitude (called trigger) of proper polarity should be applied at the

input(output) of an active device the circuit. The trigger can be a dc trigger or it can be a

pulse trigger. There are two triggering methods to change the state of multivibrator.

1. Unsymmetrical triggering

2. Symmetrical triggering.

ASTABLE MULTIVIBRATOR

Introduction:

Two cross-coupled switching circuits are connected in this arrangement. The

devices in this Multivibrator will not remain in one state (either ON or OFF) forever.

Change of state in the devices occurs continuously after a finite time interval depending

on the circuit components used. Hence this circuit has two quasistable states.

Let Q1 and Q2 be two transistors used. If Q1 is ON, then Q2 is OFF. These will

remain in this state only for a fixed time duration after which Q1 switches into the OFF

state and Q2 into the ON state without applying triggering pulse and this process is

repeated. Therefore it is also called Free running multivibrator. The output of the circuit

is a squarewave, having two time periods,T1 and T2. If T1 = T2=T/2 , then the circuit is a

symmetric astable multivibrator. If T1¹ T2, then it is called an unsymmetrical astable

multi-vibrator. The astable multivibrator is essentially a squarewave generator