14.1 Introduction

In Chapter 7, a technique for sampling, holding, and making practically identical copies of a current was described. A number of research groups ^{[1 4]} developed the idea independently, giving the class of circuits names that often reflect the application that the inventors envisioned. The term used by Eric Vittoz in Chapter 7, "dynamic current mirror" is suggestive of the historical continuity of the principle within his body of research in dynamic techniques; thus, the emphasis here is on the general utility of the circuit in any design situation to which improvement of performance through dynamic techniques may apply (some examples of these are given in Chapter 7). The term "current copier" was first used [5] by one of us, for whom analog signal processing was the main focus. In this case, the name arose from the system-level requirement for a circuit capable of distributing multiple copies of an input, output, or state variable in current form within a current-mode discrete-time analog filter. Groeneveld et al. use the term "calibration circuit", indicative of the function performed by the cell in their monolithic current-mode D/A converter. The algorthmic A/D converter reported by Nairn and Salama employs a "current matching" circuit as its essential feature, ideally eliminating dependence on the matching or ratioing of any circuit components.

These multiple geneses suggest that the time has come for this circuit, for reasons of both technological feasibility and usefulness of function. Further, the variety of names...