Pulse-encoded modulation PCM
Pulse-encoded modulation is the ideal way to convert an analog signal into binary wards, as it is encoded in the appropriate way to be sent over transmission lines that is, the signal is an embedded pulse code to convert its analog information into zeros ones.
PCM embedding is a type of The original encoding or the so-called source codec. Source coding is a conversion from an analog signal to a digital. After converting to digital signal, it is easy to process the signal i.e. decode it, filter it and remove unwanted signals.
In addition, the quality of the digital signal is better than that of the analog signal. The reason for this is that the digital signal can be retrieved easier using a comparator, and the transmission rate in different applications reaches 1.5 MB/s, as it is in the American Tl-Carrier system.
The communication lines contain amplifiers and repeaters, the aim of which is to improve the signal level and reduce the noise to the least possible.
When the signal is received, the receiver returns it to the frequency range in which it was, and then processes this signal to get rid of the noise and distortion elements that entered it. PCM embedding is commonly used in telephony and voice communications.
Which is one of the most common types of modulation, due to its capabilities, including the ability to reconfigure the digital signal consisting of a group of pulses through repeaters, in addition to the simplicity of the circuits it uses and their low cost.
The main benefit of this embedding is that it only needs a cut-off frequency of 8 kHz, as the frequency of the telephone signal is 4 kHz (and therefore 8 kHz = 2 × 4 = Fs) in order to preserve the original sound quality. The simplest PCM modulation circuit consists of an LPF filter, and it is used to remove the noise from the audio signal (information), then the information signal will be sliced (Sampler) to obtain a series of slicing values, then the signal will pass to a quantizer to quantify the segmented values.
Then the signal is sent to an encoder to encode the quantized values so the signal will be converted into a digital signal. The quantization process can be accomplished simultaneously using A/D and it is worth noting that attention should be paid to the quantization levels, for example if the PCM modulation bits equal 3, then the quantization levels equal 3^2 = 8 quantization steps.
If the number of PCM symbols is 4, then the number of levels will be 4^2, that is, the number of quantization steps is equal to 16.
The increase in the number of symbols for PCM modulation will prevent the signal from being distorted and distorted, but the field width will also increase according to the increase in data capacity. The n output pin is used to set the bandwidth.
So we need to convert the parallel data to serial data, which is a way to fulfill the PCM embed conditions
PCM Embedding Phases
Sampling the analogue signal to obtain the PAM signal
Quantifying the pulse values and rounding them to the nearest value
Encoding the values that were adopted in the second stage into a binary word, depending on the values that were determined in the second stage.
PCM Features
Low cost of digital circuits used
The ability to transmit various analogue signals, audio, video, and video
In the case of long-range digital communications, there is the possibility of retrieving PCM signals from repeaters in the ideal situation with which they started
It has a higher tolerance to noise impact than analogue systems
Obtaining long distances between repeaters, and one of its disadvantages is the need for a wide bandwidth
PCM Apps
Digital Telephone Systems
Digital audio systems in computers
Digital Audio in Computers
CD-DVD audio systems
Digital Video Systems
Coders and decoders
Telemetry systems
Space Communication where satellite images and other data are sent using PCM.
Please Check:
Introduction to Signals Modulation Part 1
Modulating process role in communication systems Part 2
The types of Modulation: Analog Modulation
The types of Modulation: Digital Modulation
Thank you.
