1 Answers
Option 4 : PAM
The main difference between analog and digital modulation is that analog modulation is a continuous signal which implies the signal changes with time. On the other hand, digital modulation is a discrete signal which means it will carry only binary information.
There are three types of analog pulse modulation techniques:
1. PAM( Pulse Amplitude Modulation): An analog modulation scheme in which the amplitude of the pulse carrier varies which is proportional to the instantaneous amplitude of the message signal.
2. PWM(Pulse width modulation): An analog modulation scheme in which the width or the duration of the time of the pulse carrier varies which is proportional to the instantaneous amplitude of the message signal.
3. PPM ( Pulse position modulation): An analog modulation scheme in which the position of the reference pulse varies according to the instantaneous sampled value of the message signal.
Digital Modulation techniques:
1. DPCM( Differential pulse code modulation): DPCM is a technique of analog to digital signal conversion which samples an analog signal and then quantizes the difference between the sampled value and its predicted value, then encodes the signal to form a digital value.
2. DM( Delta Modulation): DM is an easy way of DPCM in which the data which is to be transmitted is minimized to a 1-bit data stream.
3. ADPCM( Adaptive differential pulse code modulation): ADPCM is a technique used to convert analog signals to binary signals by taking frequent samples of the sound and expressing the value of the sampled modulation in binary form.
Thus from the above definitions, we can conclude that PAM doesn't come under a digital scheme.
Conclusion: option 4 is correct.