Thesis submitted to WARF


Interconnect Dominant Design Methodology

for DSP architectures

- A Mixed Number System based Approach



With deep submicron (DSM), the gates have become smaller and faster, whereas the amount of interconnect on a chip used to connect these small and fast gates has grown exponentially. The ratio of interconnect delay to gate delay continues to increase in favor of interconnect delay as DSM designs continue to get smaller. The result is a shift in the design paradigm based on interconnect delay dominance.


Buffer insertion techniques have been successful in reducing interconnect delay. This consumes power and occupies a large amount of the chip area. The power consumed by these delay optimal devices and wires will increase as we go into the DSM era. This thesis investigates the DSM issues in the design of DSP algorithms and architectures. The DSM issues have been analyzed in great depth with respect to interconnect dominance in FFT algorithms and architectures, as well as in DFT. One of the main findings of the thesis is that the FFT architectures suffer from high degree of interconnect dominance making them unsuitable for DSM technology when compared with DFT.


High performance, accuracy and low power are the most important design parameters of DSP architectures. In DSM based technology, while high performance can be achieved, power becomes a critical factor, which needs either a new architecture or even a new number representation. The computational complexity of DSP algorithms leads to high power consumption particularly in high performance applications. An architecture for Arithmetic Processor based on a mixed number representation is presented. Here, the sign/log number system is embedded into the residue number system. It is shown

that this mixed number representation called Logarithmic Residue Number System (LRNS) achieves low power and high performance over the Binary, Residue and sign/log number systems. It is further shown that unlike the sign/log number system, LRNS maintains an accuracy of within 1 percent of the binary number system. A special purpose power efficient instruction set for the processor is proposed.


The work presented in this thesis is expected to help in developing high performance low power DSP systems. As a case study, LRNS is shown to reduce the computational complexity in time frequency transforms like the Gabor.



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