A 20 b dynamic-range floating-point data acquisition system

The design and engineering of a floating-point data-acquisition system are described. The system has both automatic gain and software-programmable gain adjustment features. In automatic gain adjustment mode, the gain is set automatically dependent on the input amplitude so that the full conversion resolution is maintained irrespective of the signal dynamic range. A high-speed flash ADC with an approximately 35 ns conversion time is used to convert the signal quickly into 8 b data. A programmable array logic (PAL) then transfers this 8 b digital data into 12 b information for setting the gain of the variable-gain amplifier. The amplifier gain settings are all powers of two; thus, the normalization of the digitized data requires only a bit shifting operation and no complex software division. The gain information and the 12 b sampling ADC output increase the dynamic range to 20 b. The software package includes commands needed for the system initiation, automatic gain or software programmable gain selection, sampling and conversion, and data normalization