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Digital Design of Signal Processing Systems: A Practical Approach by Shoab Ahmed Khan

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9

Designs based on Finite State Machines

9.1 Introduction

This chapter looks at digital designs in which hardware computational units are shared or time-multiplexed to execute different operations of the algorithm. To highlight the difference between time-shared and fully dedicated architecture (FDA), the chapter first examines examples while assuming that the circuit clock is at least twice as fast as the sampling clock. It is explained that, if instances of these applications are mapped on a dedicated fully parallel architecture, they will not utilize the HW in every clock cycle. Time sharing is the logical design decision for mapping these applications in HW. These designs use the minimum required HW computational resources and then share them for multiple computations of the algorithm in different clock cycles. The examples pave the way to generalize the discussion to time-shared architecture.

A synchronous digital design that shares HW building blocks for computations in different cycles requires a controller. The controller implements a scheduler that directs the use of resources in a time-multiplexed way. There are several options for the controller, but this chapter covers a hardwired state machine-based controller that cannot be reprogrammed.

The chapter describes both Mealy and Moore state machines. With the Mealy machine the output and next state are functions of the input and current state, whereas with the Moore machine the input and current state only compute the ...

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