Logarithmic Analog-to-Digital Converters: A Survey

Analog-to-digital converters (ADC) with logarithmic law are receiving particular attention from system and circuit designers. They can be applied to solve many problems of data acquisition and encoding found in almost all the fields of experimental physics and instrumentation dealing with analog variables with several decades of dynamic range, where a constarnt relative accuracy, rather than a constant absolute accuracy, is required. Spme proposals and realizations of logarithmic ADC (LADC) already presented in the literature are discussed as well as some new ideas organized according to three classes of schemes. The first can be viewed as the cascade connection of an analog logarithmic information converter and a conventional ADC; while in the second, the LADC is entirely digital and follows the ADC; and in the third, the logarithmic conversion and the A/D conversion are performed by the same structure and cannot be easily distinguished. An analysis is made of the performances of the various possible realizations as well as of their complexity.