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What is MAC Architecture


MAC is the composition of adders, multipliers and accumulators. Multiplier and adder delays play an important role for the design of MAC. For the enrichment of the speed operation Sklansky adders is used. One implementation of the multiplier could be as a parallel array multiplier. The inputs of the MAC are fetched from the memory location and fed to the multiplier block of the MAC, which will perform the multiplication and give the results to the adder. The function of the adder block is performing the accumulation of the results, and then the results are stored in the memory locations. The function of the conventional MAC unit is given by the following equation


Fig. 1 indicates the functional block diagram of the MAC. Fig. 2 indicating the architecture of the MAC diagram which has been designed in this paper. The design consists of one 4 bit parallel adder based Wallace tree multiplier , one 10 bit accumulator register, one control logic/DeMUX block, one 8 bit register. The two 4 bit numbers are multiplied and stored in 8bit registers. In first clock pulse the numbers are multiplied and the result is added with zero.

Demux are used to determine whether the generation of convolution sum operation is over. If ctrl signal of demux 0 then the operation is over else eight bit results are again fed to the accumulator registers. The two new numbers are multiplied in the second clock pulse and the product is added with first eight bit results. The process is repeated for four times until the multiplication over. The ctrl signal generation circuit has been shown in Fig.3. This circuit counts the number of clock pulses. The mentioned circuit is a down counter which is set at 410. For each clock pulse the down counter is decremented by one. When the forth clock pulse is reached the ctrl signal is 0 and it remains 0 until a new operation is executed and sets the MAC output results.




Table 1: Power delay analysis of MAC


Pre layout Simulation

Post Layout Simulation

Conventional MAC





Average power(w)




Lkg. Power (w)












Fig.10. layout of 4 point MAC