Development of the Area-Reducing Active "Coil-Enhancement" Principle, Practiced Onto an ADSL-POTS Splitter

This paper describes the theory behind the ``coil-enhancement{''} principle: The impedance of an inductor is made controllable as a function of the frequency by means of a transconductance function g(m) (s) that is located in the feedback loop. In order to show the potential of the coil-enhancement circuit, the effect of several basic transconductance functions onto the synthesized impedance is presented. The specific case of g(m) (s) similar to s(-1) produces the coil-enhancement situation and is discussed in detail. One drawback of the coil-enhancement circuit is found in the series resistance of a second inductor, also positioned in the feedback loop. The influence of this series resistance onto the synthesized impedance is addressed and a work-around is presented. A newly developed active ``plain old telephone service{''} (POTS) splitter, based upon the coil-enhancement principle, is derived from a fully passive POTS splitter in which two large inductors are merged together into one active inductor. The active POTS splitter is fully tested and is found compliant with the standard ``TS 101 952-1-1 V1.2.1 (option A){''} of the European Telecommunications Standards Institute. The area reduction that comes together with the passive-to-active conversion is 40%.