Tunable Elements

Abstract

Tunable elements are essential for any adaptive architecture to operate successfully. By definition, a tunable circuit is a circuit that enables the change of one or more of its key parameters using a voltage or a current control signal. Thus, the presence of such circuits provides a knob to tweak the performance of the whole system, and if implemented within an adaptive loop, then this tweaking could be achieved automatically as outlined in chapter 2. Examples of available tunable elements would be tunable resistors, capacitors, transconductors, amplifiers, and offset comparators. Chapter 2 gave an overview of the techniques available to implement tunable resistors, capacitors, and transconductors. Since voltage-controlled transconductors are particularly very popular, this chapter focuses on discussing circuit implementations that enable higher performance, wider control range, and more robust programmable performance. In addition to voltage-controlled transconductors, and since programmable comparators were not discussed in chapter 2, this chapter will also discuss the general characteristics of comparators with an emphasis on available techniques for implementing a specific class of them, i.e. Offset Comparators. It then proceeds with presenting a circuit design technique for implementing highspeed voltage-controlled offset comparators, where higher performance and more accurate control over the offset could be achieved in a robust fashion.