The wireless and high speed data communications industry is driven by the ability to achieve high levels of integration in electronics. The ever increasing circuit complexity and demands to reduce power consumption have pushed available technology to its limits. These limits have been acceptable in the case of the circuitry needed to realize the digital signal processing functions, but these same limits are not at the threshold of compromising the performance of the necessary analog signal processing circuitry which must be exist at the front end of most systems. The research here involves the development of a new concept in the design of this analog circuitry that allows very low voltage operation of high frequency circuits. The "Log Domain" filters studied here permit the development of next generation electronics that will operate using less power, which translates, for example, to fewer batteries in portable equipment. Log Domain, and more generically Exponential State Space (ESS), filters are the result of a new paradigm in linear filter synthesis. Specifically, the nonlinearity of the transistors which comprise the active circuitry is designed explicitly into the circuit formulation. The investigators are studying the mathematics of this design approach more fully so as to improve our understanding of these circuits. This research effort explores the effects of transistor parasitics, such a finite beta, Early effect, and bulk resistance, on Log Domain filter performance. In addition, the state space mappings used to generate the design equations for these filters are being studied to generalize the formulation to include both class A and class AB filters. Results on noise and distortion performance of these filters is also being examined. Finally, the practical performance of these filters is being investigated using a test IC fabricated by Analog Devices, Inc.
