Research for Mixed Signal Electronic Technologies: A Joint Initiative Between NSF and SRC: Inter-Pulse-Interval Based Mixed Signal Representations

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ABSTRACTAlthough digital signal representation has become almost universal, there are still many areas where an analog representation is required to interface with an analog world or to meet various other objectives such as power dissipation, frequency, or cost. In these domains analog signal representation is essential for many input modalities such as instrumentation, sensor interfaces, and communications. Likewise, there are related output applications, such as biomedical actuation and industrial control. In addition, the needs of wireless and fiber-optical communication have reinvigorated analog design. However, there are serious problems concerning how to keep these analog components on a reasonable scaling curve as Moore's law continues unabated in the digital domain, and in integrating analog representations into large, complex digital systems ("system on a chip"). The purpose of this proposal is to study a new approach to representing analog signals that we believe will integrate more cleanly into these deep submicron, single-chip systems. Today analog signals are almost exclusively represented by current or voltage quantities. Our proposal is to borrow a page from neuroscience and to use the Inter-Pulse-Interval (IPI) between single-bit, asynchronous pulses to represent analog quantities. We are proposing to develop a mixed-mode analog/digital cell library and design methodology based on IPI representation and the associated computation elements, and to engineer a case study to illustrate the outcomes. As we move to deep submicron and then on to the nanometer/molecular devices, the problems that digital encounters with scaling, such as threshold inconsistency, subthreshold currents, hot-electron effects, doping variability, substrate coupling, and transmission line and complex cross-talk effects, are even more serious for analog circuitry. IPI representations will provide significantly better immunity to these effects, as well as to the more traditional process, temperature, and reference voltage variations. For most applications, pulse based analog systems will require less power. There are numerous advantages to using pulses or pulses to communicate. They are significantly more immune to noise. An approximate analogy would be that of AM versus FM radio signal representation. The outcomes of the proposed research are Create a library of basic communication, computation (arithmetic and logic) and conversion building blocks;Design, implementation and testing of a case study using the derived building blocks and methodology;Document an IPI-based design methodology