written 5.5 years ago by | modified 5.5 years ago by |
Subject: Priniciples of Communication Engineering
Difficulty : Medium
Marks : 10
written 5.5 years ago by | modified 5.5 years ago by |
Subject: Priniciples of Communication Engineering
Difficulty : Medium
Marks : 10
written 5.5 years ago by | modified 5.4 years ago by |
Pulse Width Modulation (PWM) :
As its name suggests this method of modulating the carrier signal alters the width of the digital pulses in accordance with the modulating signal. The width of the pulse is proportional to the instantaneous amplitude of the modulating signal. For a positive modulating signal the width of the pulse increases proportionally, and for a negative modulating signal the width of the pulse decreases proportionally.
Generation:
The simplest analog form of generating fixed frequency PWM is by comparison with a linear slope waveform such as a sawtooth. As seen in the figure below the output signal goes high when the sine wave is higher than the sawtooth. This is implemented using a comparator whose outputvoltage goes to a logic HIGH when ne input is greater than the other.
Demodulation:
Waveforms: