Digital Signal Processor: Architecture and Performance

Digital signal processing has become more and more important in telecommunications. As new products and services are offered, the amount of required signal processing continues to increase. In addition, signals are becoming digital, especially in applications where the superior stability and accuracy of these signals is either necessary or more attractive. Digital signal processing is also prompted by the introduction of digital switching offices and digital transmission systems. It is made possible by the continuous, rapid growth of the silicon LSI and VLSI capabilities. The latter have made it inexpensive to build complex processors--so inexpensive that it is cost-effective even to use A/D conversion and digital signal processing in some analog systems. We indeed visualize the extension of the digital network all the way to the subscriber phone! 1449 In this paper, we describe a single-chip, digital signal processor recently developed for Bell System use. The device, known as Digital Signal Processor (DSP) is a general-purpose building block which can be programmed to perform a variety of digital signal processing functions. Examples of these are filtering, equalization, modulation, tone detection, speech coding, and Fast Fourier Transform. The DSP is fabricated in depletion-load NMOS and packaged in a 40-pin DIP. It is customized to perform specific signal processing functions by means of an on-chip read only memory (ROM) containing the program and fixed data. The device also contains a random access memory (RAM) for writing and reading variable data, a Control Unit, an Arithmetic Unit (AU), an Address Arithmetic Unit (AAU), and appropriate Input/Output (i/o) circuitry.