DIGITAL COMMUNICATION SYSTEM Basic

DIGITAL COMMUNICATION SYSTEM

Digital communication is a mode of communication. It occurs when the information or the thought is encoded digitally as discreet signals and then is electronically transferred to the receiver.

Input Transducer (Source): - it is a device which convert analog signal to digital signal.  Source also can be digital or analog.  e. g.  Audio signal,  vedio signal  Digital binary numbers or Data Base Information

Source Encoder(Data Compressor) : - The signal produced by source is converted into digital signal consists of 1′s and 0′s. Source Encoding or Data Compression The process of efficiently converting the output of analog or digital source into a sequence of binary digits is known as source encoding.

Channel encoder : - it is to introduce some redundancy, in control manner in the binary information sequence which can be transmit to receiver

Digital modulator: - Binary sequence is pass digital modulator which in terms convert the sequence into electrical signal which can be transmit on the channel

Comparison between Analog communication and digital communication

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Static RAM (SRAM) and Dynamic RAM (DRAM) (Part-2)

• Static Random Access Memory (SRAM)

SRAM (static RAM) is random access memory (RAM) that retains data bits in its memory as long as power is being supplied. Unlike dynamic RAM (DRAM), which stores bits in cells consisting of a capacitor and a transistor

• SRAM does not have to be periodically refreshed. 
• Static RAM provides faster access to data and is more expensive than DRAM. S
• RAM is used for a computer's cache memory and as part of the random access memory digital-to-analog converter on a video card.

• Dynamic Random Access Memory (DRAM)

Dynamic random access memory (DRAM) is a type of memory that is typically used for data or program code that a computer processor needs to function. DRAM is a common type of random access memory (RAM) used in personal computers (PCs), workstations and servers.

• Random access allows the PC processor to access any part of the memory directly rather than having to proceed sequentially from a starting place. 
• RAM is located close to a computer’s processor and enables faster access to data than storage media such as hard disk drives and solid-state drives. 

Expansion of word length and capacity (Part 3)

• Expansion of word length

Word length expansion connects memory devices in parallel, so that the address range is unchanged but the data is wider. The number of data units is unchanged, but the size of the data units increases.

Word length expansion usually requires external logic to implement, as the memory devices operate in unison and therefore share all address, data, and control lines.

• Expansion of word Capacity

Memory capacity expansion connects memory devices “end-to-end,” so that the data width is unchanged but the address range increases. The size of the data units is the same, but the number of data units increases.
Memory capacity expansion usually requires some external logic, as only one memory device is active at a time and the system must provide some means of distinguishing the two. Typically an inverter is used on the chip select line on one of the memory devices, so that selecting one will automatically de-select the other.