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ABSTRACT:

As we digital communication offers several important advantages as compared to analog

communication .However to handle the transmission of analog message signals by digital means

the signal has to undergo an analog to digital conversion PCM is most common technique for

that. In PCM we first sample the signal then quantize the sampled signal and then encode andthen transmit. But in PCM we transmit all the bits which are used to code a sample .Hence

signaling rate and transmission channel bandwidth are quite large in PCM. To overcome this

problem Delta Modulation is used.In this project we are going to do Delta Modulation and

Demodulatiomn.We use commsim software for that.

INTRODUCTION:

Delta Modulation:

(DM or -modulation) is an analog-to-digital and digital-to-analog signal conversion techniqueused for transmission of voice information where quality is not of primary importance. DM is the

simplest form of differential pulse-code modulation (DPCM) where the difference betweensuccessive samples is encoded into n-bit data streams. In delta modulation, the transmitted data is

reduced to a 1-bit data stream.

Its main features are:

y the analog signal is approximated with a series of segmentsy each segment of the approximated signal is compared to the original analog wave todetermine the increase or decrease in relative amplitude

y the decision process for establishing the state of successive bits is determined by thiscomparison

y only the change of information is sent, that is, only an increase or decrease of the signalamplitude from the previous sample is sent whereas a no-change condition causes the

modulated signal to remain at the same 0 or 1 state of the previous sample.

To achieve high signal-to-noise ratio, delta modulation must use oversampling techniques, that

is, the analog signal is sampled at a rate several times higher than the Nyquist rate.

Derived forms of delta modulation are continuously variable slope delta modulation, delta-sigmamodulation, and differential modulation. The Differential Pulse Code Modulation is the super set

of DM.

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Principle:

Rather than quantizing the absolute value of the input analog waveform, delta modulation

quantizes the difference between the current and the previous step.

Modulator circuit:

Demodulator circuit:

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SIMULATON RESULT