PHENO: a new concept of hybrid computing elements

PHENOs are based on the well-known fact that a digital-to-analog converter with variable reference (MDAC) can produce the product of an analog and a digital variable. While for multiplication and division this principle can be used directly, it has to be modified for function generation. In order to obtain a system of computing elements in which any input or output variable can exist in analog or digital form, optionally, DACs and ADCs (analog-to-digital converters) are combined. The straight-line-segment approximation of arbitrary functions is done by splitting the (digital) argument of the function in two parts. The first group of r bits defines the nearest preceding breakpoint, while the second group of (n-r) bits is used for linear interpolation (n being the digital word-length). In a second method of function generation, which is particularly suited for multivariable functions, digital table look-up is combined with analog interpolation. On the base of PHENOs, this procedure provides minimum table lookup execution time and avoids stability problems.