Unit1 Pulse Mod

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Pulse Modulation



PULSE MODULATIONy A system of modulation in which pulses are altered

and controlled in order to represent the message to becommunicated.

y the modulation of the amplitude, a characteristic, etc.of a sequence of pulses in order to convey information:often used in codes

y The aim of pulse modulation methods is to transfer a

narrowband analog signal, for example a phone callover a wideband baseband channel or, in some of theschemes, as a bit stream over another digitaltransmission system.



Pulse Amplitude Modulation (PAM)y is the simplest form of pulse modulation. This

technique transmits data by varying the voltage or

power amplitudes of individual pulses in a timedsequence of electromagnetic pulses. In other words,the data to be transmitted is encoded in the amplitudeof a series of signal pulses. P A M can also be used forgenerating additional pulse modulations.





Bandwidthy is the difference between the upper and lower

frequencies in a contiguous set of frequencies. It is

typically measured in hertz, and may sometimes referto passband bandwidth, sometimes to baseband bandwidth, depending on context

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Q uantizationy is the process of approximating ("mapping") a

continuous range of values (or a very large set of

possible discrete values) by a relatively small ("finite")set of ("values which can still take on continuousrange") discrete symbols or integer values.



Pulse-code modulation (PCM)y is a method used to digitally represent sampled analog

signals, which was invented by A lec Reeves in 1937. It is

the standard form for digital audio in computers and various Blu-ray , Compact Disc and DVD formats, as well as other uses such as digital telephone systems.

y A PCM stream is a digital representation of an analog

signal, in which the magnitude of the analogue signalis sampled regularly at uniform intervals, with eachsample being quantized to the nearest value within arange of digital steps.



Pulse-code modulation (PCM)y PCM streams have two basic properties that determine

their fidelity to the original analog signal: the

sampling rate, which is the number of times persecond that samples are taken; and the bit depth, which determines the number of possible digital values that each sample can take.



Pulse-code modulation (PCM)

Sampling and quantization of a signal (red) for 4-bit PCM



Time-division multiplexingy is a type of digital or (rarely) analog multiplexing in

which two or more signals or bit streams are

transferred apparently simultaneously as sub-channelsin one communication channel, but are physically taking turns on the channel.

y The time domain is divided into several recurrent

timeslots of fixed length, one for each sub-channel. A

sample byte or data block of sub-channel 1 istransmitted during timeslot 1, sub-channel 2 duringtimeslot 2, etc.



Differential Pulse Code Modulationy is a procedure of converting an analog into a digital

signal in which an analog signal is sampled and then

the difference between the actual sample value and itspredicted value (predicted value is based on previoussample or samples) is quantized and then encodedforming a digital value.

y

DPCM code words represent differences betweensamples unlike PCM where code words represented asample value.



Delta modulationy is an analog-to-digital and digital-to-analog signal

conversion technique used for transmission of voice

information where quality is not of primary importance.

y DM is the simplest form of differential pulse-codemodulation (DPCM) where the difference between

successive samples is encoded into n-bit data streams.In delta modulation, the transmitted data is reducedto a 1-bit data stream.



Adaptive delta modulationy continuously variable slope delta modulation (CV SD)

is a modification of DM in which the step size is not

fixed. Rather, when several consecutive bits have thesame direction value, the encoder and decoder assumethat slope overload is occurring, and the step sizebecomes progressively larger.

y

Otherwise, the step size becomes gradually smallerover time. A DM reduces slope error,at the expense of increasing quantizing error.This error can be reducedby using a low pass filter.

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Unit1 Pulse Mod