Thursday 28 May 2015

Digital Electronics

Digital electronics or digital (electronic) circuits is related with digital signals.digital signal are those whose represented by discrete interval of times rather then continous time of intervals.
E&l instruments 325-1455 digital electronics board 5
In most cases the number of these states is two, and they are represented by two voltage bands: one near a reference value (typically termed as "ground" or zero volts), and the other a value near the supply voltage. These correspond to the "false" ("0") and "true" ("1") values of the Boolean domain i.e.binary code.
In a digital system, a more precise representation of a signal can be obtained by using more binary digits to represent it While this requires more digital circuits to process the
signals, each digit is handled by the same kind of hardware, resulting in an easily scalable system.Computer-controlled digital systems can be controlled by software, allowing new functions to be added without changing hardware.Information storage can be easier in digital systems than in analog ones. The noise-immunity of digital systems permits data to be stored and retrieved without degradation.
the digital circuit are much faster , Modern electronic digital logic routinely switches at five gigahertz (5×109 hertz), and some laboratory systems switch at more than a terahertz (1×1012 hertz).

Digital circuit Design started with relays. Relay logic was relatively inexpensive and reliable, but slow.
Later, vacuum tubes were used.These were very fast, but generated heat, and were unreliable because the filaments would burn out.In the 1950s, special "computer tubes" were developed with filaments that omitted volatile elements like silicon. These ran for hundreds of thousands of hours.
The first semiconductor logic family was resistor–transistor logic. This was a thousand times more reliable than tubes, ran cooler, and used less power, but had a very low fan-in of three. Diode–transistor logic improved the fanout up to about seven, and reduced the power.
Transistor–transistor logic (TTL) was a great improvement over these. In early devices, fanout improved to ten, and later variations reliably achieved twenty. TTL was also fast, with some variations achieving switching times as low as twenty nanoseconds. TTL is still used in some designs.

Emitter coupled logic is very fast but uses a lot of power. It was extensively used for high-performance computers made up of many medium-scale components.
 the most common digital integrated circuits built today use CMOS logic, which is fast, offers high circuit density and low-power per gate. This is used even in large, fast computers, such as the IBM System z.
In 2009, researchers discovered that memristors can implement a boolean state storage (similar to a flip flop, implication and logical inversion), providing a complete logic family with very small amounts of space and power, using familiar CMOS semiconductor processes.
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