Скачать или смотреть Lecture No - 13 ( Demodulation of PWM )

To recover the original audio signal from a PWM signal, a decoder or demodulator is need in the receiver circuit.There are two common techniques used for pulse-width demodulation. One method is that the PWM signal must first be converted to a pulse-amplitude modulation (PAM) signal and then passed through a low-pass filter. The PWM signal is applied to an integrator and hold circuit. When the positive edge of pulse appears, the integrator generates ramp output whose magnitude is proportional to the pulse width. After the negative edge, the hold circuit maintains the peak ramp voltage for a given period and then forces the output voltage to zero. The waveform is the sum of a sequence of constant-amplitude and constant-width pulse generated by demodulator. This signal is then applied to the input of clipping circuit, which cuts off the portion of signal below the threshold voltage and outputs the reminder. Therefore the output of clipping circuit is a PAM signal whose amplitude is proportional to the width of PWM signal. Finally, the PAM signal passes through a simple low-pass filter and the original audio signal is obtained.

List of Previous Lectures
Lecture 12: -    • Lecture - 12 ( Quantization )  
Lecture 11: -    • Lecture No - 11 ( Pulse Position Modulation )  
Lecture 10: -    • Lecture No. -10 ( Pulse Width Modulation )  
Lecture 9: -    • Lecture No - 9 (Pulse Amplitude Modulation )  
Lecture 8: -    • Lecture No - 8 ( PULSE MODULATION)  
Lecture 7: -    • Lecture No - 7 (Type of Sampling  ((Part-I...  
Lecture 6: -    • Lecture No -6 ( Types of Sampling ) Part -(I)  
Lecture 5: -    • Lecture No 5 ( Numerical  of Band Pass Sam...  
Lecture 4: -    • Lecture No 4 ( Sampling Theorem for Band P...  
Lecture 3: -    • Lecture No 3 ( Sampling Theorem for Low Pa...  
Lecture 2: -    • Lecture No - 2 (Block Diagram of Digital C...  
Lecture 1:-    • Lecture No 1 ( Basics of Communication )