21-05-2013, 04:06 PM
PULSE AMPLITUDE MODULATION & DEMODULATION
Aim:
To generate the Pulse Amplitude modulated and demodulated signals
Theory:
PAM is the simplest form of data modulation. The amplitude of uniformly spaced pulses is varied in proportion to the corresponding sample values of a continuous message m (t).
A PAM waveform consists of a sequence of flat-topped pulses. The amplitude of each pulse corresponds to the value of the message signal x (t) at the leading edge of the pulse.
The pulse amplitude modulation is the process in which the amplitudes of regularity spaced rectangular pulses vary with the instantaneous sample values of a continuous message signal in a one-one fashion.
Procedure:
1. Connect the circuit as per the circuit diagram shown in the fig 3
2. Set the modulating frequency to 1KHz and sampling frequency to 12KHz.
3. Observe the o/p on CRO i.e. PAM wave.
4. Measure the levels of Emax & Emin
5. Feed the modulated wave to the low pass filter as in fig 4.
6. The output observed on CRO will be the demodulated wave.
7. Note down the amplitude (p-p) and time period of the demodulated wave. Vary the amplitude and frequency of modulating signal. Observe and note down the changes in output.
8. Plot the wave forms on graph sheet.