Mani Raj Paul

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Delta Modulation modulatin, in which the sampling rate is much higher and in which the stepsize after quantization is of a smaller value Δ , such a modulation is termed as delta modulation . Features of Delta Modulation Following are some of the features of delta modulation. An over-sampled input is taken to make full use of the signal correlation. The quantization design is simple. The input sequence is much higher than the Nyquist rate. The quality is moderate. Delta Modulator The Delta Modulator comprises of a 1-bit quantizer and a delay circuit along with two summer circuits. Following is the block diagram of a delta modulator.  

 Sr. No.              Parameter PAM PWM PPM 1 Type of Carrier Train of Pulses Train of Pulses Train of Pulses 2 Variable Characteristic of the Pulsed Carrier Amplitude Width Position 3 Bandwidth Requirement Low High High 4 Noise Immunity Low High High 5 Information Contained in Amplitude Variations Width Variations Position Variations 6 Power efficiency (SNR) Low Moderate High 7 Transmitted Power Varies with amplitude of pulses Varies with variation in width Remains Constant 8 Need to transmit synchronizing pulses Not needed Not needed Necessary 9 Bandwidth depends on Bandwidth depends on the width of the pulse Bandwidth depends on the rise time of the pulse Bandwidth depends on the rise time of the pulse 10 Transmitter power Instantaneous transmitter power varies with the amplitude of the pulses Instantaneous transmitter power varies with t...

In Differential Phase Shift Keying DPSK the phase of the modulated signal is shifted. No reference signal is considered here. , if the data bit is Low i.e., 0, then the phase of the signal is not reversed . If we observe the above waveform, we can say that the High state represents an M in the modulating signal and the Low state represents a W in the modulating signal.   DPSK Modulator DPSK is a technique of BPSK, in which there is no reference phase signal. Here, the transmitted signal itself can be used as a reference signal. DPSK encodes two distinct signals, i.e., the carrier and the modulating signal with 180° phase shift each. The serial data input is given to the XNOR gate and the output is again fed back to the other input through 1-bit delay. The output of the XNOR gate along with the carrier signal is given to the balance modulator, to produce the DPSK modulated signal. DPSK Demodulator In DPSK demodulator, the phase of the reversed bit ...