A Floating-Point A/D Converter for Smart Sensors

A binary scaled programmable current source has been designed for use in a non-linear A/D converter for smart sensors applications. The non-linear conversion is achieved by using accurate binary-weighted current sources with emitter scaling and analog current switches. The A/D converter implements two programmable current sources, the first is used to determine the exponent, while the second is used to determine the mantissa in a floating point representation number. The current source and the required electronics are implemented using a bipolar process in silicon which makes it compatible with silicon sensors. A special layout has been implemented in the design to compensate for mismatch gradients over the chip.