Fast Adders Essay

INTRODUCTION

Addition operation is the most important function of digital system. Adder is only not used for the arithmetic operation but also necessary to all modern computers. Adders occupies critical path in key areas of microprocessor, fast adders are prime requirement for the design of fast processing system. Many fast adders are available but the design of high speed with low power and less area adders are still challenging. In modern computers, multiple ALU’S with wide adders and multiple execution core units on the same chip creates thermal hotspots and large temperature gradients. This affects the circuit and increasing the cooling cost of the system. Adders should have highest performance with least amount of power dissipation and

Shannon expansion is a very useful technique for pre-computation based on low power design in sequential logic circuits, due to its multiplexing properties [6]. GDI cells can be successfully used for low power design for combinational digital circuit, while combining two approaches, Shannon expansion and combinational logic where transitions of logic input values are prevented from propagating through the circuit.

Using GDI functions Ripple-carry (RCA) and Carry look ahead adders are presented in [4]. A Ripple Carry Adder (RCA) is an optimized area-efficient adder design [1]. The layout of ripple carry adder is simple, which allows fast design time but it is relatively slow, since for each full adder must wait for carry output bit, is to be calculated by previous adder. The maximum delay in RCA is computed from the Cin to Cout of carry, passing through each full adder circuit along the way.

III NOVEL FULL

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