Systems for analog and mixed signal processing in integrated technology based on network theory

Despite the overwhelming trend of digitization of electronic systems, and many indisputable advantages of having digital signal processing compared to analog, hardware towards the real, outside world, is a part of the overall mixed system and remains mostly analog. This analog part, in most IC-system chips is well known as “analog-front-end” (AFE). Therefore, the analog electronic circuits as part of an AFE, not only will remain an important part of most integrated systems, but often represent one of the bottlenecks in achieving low power consumption and small area on an integrated circuit. This explains why the development and design of new and improved (from the standpoint of IC design) analog electrical circuits still plays an important role — and will likely continue to play an important role — in the development of new and advanced systems-on-chip. One of the types of analog circuits that have traditionally lagged behind the others in the process of designing in integrated-circuit form is frequency-selective filters. Filters on the chip, may not have inductances; in the time-continued domain they are the so-called ‘active RC filters’, which means they combine resistors and capacitors with voltage or current amplifiers. Reasons for the delay in the design of integrated active-RC filters are manifold, but one of the most important are theirs large components tolerances (as a consequence there is a need for circuit tuning), voltage noise within the circuit, limited dynamic range and the size of the chip. The new and innovative ideas arise in the design of time-continuous filters from the application of network and transmission line theory. Some special situations in communication systems require novel topologies in filter design, and solve different problems that are important in modern analog IC design. The new approaches are: (i) savings in chip area in elliptical filters in the integrated design using signal-flow graphs, (ii) reducing the sensitivity to variations in the component values by application of negative feedback, (iii) filter partitioning for efficient onchip filter tuning, and (iv) the new structure of the active-RC filter that is used to build ADSL splitter; a stability problem to be solved with different telephone-line terminations in different countries. All four systems are suitable to be designed in the analog filter IC design.