Every action of the computer takes place in tiny steps, each a billionth of a second long. A simple transfer of data may take only one step; complex calculations may take many steps. All operations, however, must begin and end according to the clock's timing signals.
The use of a central clock also creates problems. As speeds have increased, distributing the timing signals has become more and more difficult. Present-day transistors can process data so quickly that they can accomplish several steps in the time that it takes a wire to carry a signal from one side of the chip to the other. Keeping the rhythm identical in all parts of a large chip requires careful design and a great deal of electrical power. Wouldn't it be nice to have an alternative?
Clock less approach, which uses a technique known as asynchronous logic, differs from conventional computer circuit design in that the switching on and off of digital circuits is controlled individually by specific pieces of data rather than by a tyrannical clock that forces all of the millions of the circuits on a chip to march in unison. It overcomes all the disadvantages of a clocked circuit such as slow speed, high power consumption, high electromagnetic noise etc.
For these reasons the clock less technology is considered as the technology which is going to drive majority of electronic chips in the coming years.
1.2 Clock Concept
The clock is a tiny crystal oscillator that resides in the heart of every microprocessor chip. The clock is what which sets the basic rhythm used throughout the machine. The clock orchestrates the synchronous dance of electrons that course through the hundreds of millions of wires and transistors of a modern computer.
Such crystals which tick up to 2 billion times each second in the fastest of today's desktop personal computers, dictate the timing of every circuit in every one of the chips that add, subtract, divide, multiply and move the ones and zeros that are the basic stuff of the information age.
Conventional chips (synchronous) operate under the control of a central clock, which samples data in the registers at precisely timed intervals. Computer chips of today are synchronous: they contain a main clock which controls the timing of the entire chips.
One advantage of a clock is that, the clock signals to the devices of the chip when to input or output. This functionality of synchronous design makes designing the chip much easier. The circuit which uses global clock can allow data to flow in the circuit in any manner of sequence and order does not matter.
Figure 1.1: Global Clock
The diagram above shows the global clock is governing all components in the system that need timing signals. All components operate exactly once per clock tick and their outputs need to be ready and next clock tick.
1.3 Synchronous Circuits
The clock is a tiny crystal oscillator that resides in the heart of every microprocessor r chip. It synchronizes the motion of electrons throughout the millions of wires and transistors of a digital computer. Such crystals, which generate frequencies of about 4 GHz in the fastest of today’s desktop personal computers, dictate the timing of operation of every circuit in every chip, that perform a wide range of functions ranging from moving binary data to performing complex mathematical calculations. These conventional synchronous chips, which operate under the control of a central clock, process the data in the registers at precise time intervals.
Figure 1.2: Synchronous Logic
Figure 1.2 shows the working model of a synchronous circuit. In this example, the circuit performs all actions on the leading edge of the...