Amplitude Modulation

GENERATION OF AMPLITUDE MODULATION

Aim:  Generate different types of amplitude waveforms for various modulation index.  Plot the graphs of all sequences thus generated. SOFTWARE USED:  MULTISIM version 10.1 CIRCUIT DIAGRAM

DESCRIPTION OF THE IC The AD633 is a functionally complete, four-quadrant, analog multiplier. It includes high impedance, differential X and Y inputs and a high impedance summing input (Z). The low impedance output voltage is a nominal 10 V full scale provided by a buried Zener. The AD633 is the first product to offer these features in modestly priced 8-lead plastic DIP and SOIC packages. The AD633 is laser calibrated to a guaranteed total accuracy of2% of full scale. Nonlinearity for the Y-input is typically less than 0.1% and noise referred to the output is typically less than100 V rms in a 10 Hz to 10 kHz bandwidth. A 1 MHz bandwidth,20 V/s slew rate, and the ability to drive capacitive loads make the AD633 useful in a wide variety of applications where simplicity and cost are key concerns.

PROCEDURE: 1. The above circuit is implemented using the tools of MULTISIM software. 2. The function generator corresponding to the carrier and the message signal are connected at the right positions. 3. The CRO is connected at the output of the circuit. 4. The modulation indices for various types of modulation say, under modulation, 100% modulation and Over modulation using the measuring prompt.

% of modulation index

m

Emax  Emin  100 Emax  Emin

Find the values for m at

(50%) and

Design for m=

CASE -1: When m=

m

Emax  Emin  100 Emax  Emin

CASE-2: When m=

m

Emax  Emin  100 Emax  Emin

i.

0.5,0.9

ii.

0.4,0.8

iii.

0.3,0.7

iv.

0.2,0.6

(90%)

Output Waveforms when Am1(over modulation)

RESULT: The modulation indices, maximum and minimum values of the modulated wave are calculated and the respective graph is obtained.

GENERATION OF AMPLITUDE MODULATION

Aim:  Generate different types of amplitude waveforms for various modulation index.  Plot the graphs of all sequences thus generated. SOFTWARE USED:  MATLAB version 7.11.0(R2010b) MATLAB CODE: clear all; close all; t=0:.01:5; Am=input('enter the message amplitude'); Ac=1; m=Am*cos(2*pi*.5*t); c=Ac*cos(2*pi*10*t); y=((1+m).*c); subplot(3,1,1); plot(t,m); subplot(3,1,2); plot(t,c); subplot(3,1,3); plot(t,y);

THEORY: When represented in time domain: Let the modulating wave be m(t). m(t)=Amcos(2*pi*fm*t) Let the high frequency wave or the carrier wave be c(t) C(t)=Ac*cos(2*pi*fc*t) If the modulating signal is represented as s(t), then S(t)=Ac{1+Ka*m(t)}cos(2*pi*fc*t). Where Ka=amplitude sensitivity. PROCEDURE: 1. The code for the amplitude modulation is generated. 2. The generated code is executed in the MATLAB software. 3. The corresponding graphs for the various types of modulation techniques are plotted.

Find the values for m at

(50%) and

Design for m=

CASE -1: When m=

m

Emax  Emin  100 Emax  Emin

CASE-2: When m=

m

Emax  Emin  100 Emax  Emin

i.

0.5,0.9

ii.

0.4,0.8

iii.

0.3,0.7

iv.

0.2,0.6

(90%)

Output Waveforms when Am1(over modulation)

RESULT: The graphs for various types of modulation say under modulation, 100% modulation and Over modulation are plotted.