Analog Integrated Circuits and Signal Processing, 38, 83–101, 2004 c © 2004 Kluwer Academic Publishers. Manufactured in The Netherlands. Current Mode, Voltage Mode, or Free Mode? A Few Sage Suggestions

Abstract. Many claims have been made about the benefits of a current-mode (CM) approach to IC design. The term is used to draw attention to some kind of special dependence on currents as signals, often without a clear orientation to the broader field, referring instead to recent CM papers. Its use suggests a significant and valuable distinction over “conventional ” solutions, perhaps in the hope that this perspective, with an element of novelty at the cell level, will influence circuit design in the stringent context of IC production. This paper asks: What factors unambiguously define a current-mode circuit, and formally differentiate it from standard realizations of some function? Can one point to any compelling, and in the most favorable cases unique, advantages? Are these cells clearly of general value, capable of widespread utility? These issues are examined from the critical viewpoint that no circuits carry the entire functional burden by the exclusive use of either currents or voltages, and very few fully exploit the specific, but narrow, benefits of CM concepts. Real-world product development invariably demands the vigilant and full embrace of what might be called the Free Mode perspective, but merely as a mnemonic, not a classification. Key Words: current mode; analog design techniques 1