UFC Solution for Gas & Water Meters
The AS6040 system is made of four major blocks: supervisor, frontend, post processing and interface. The supervisor manages all tasks and is the master of the whole system, making the AS6040 autonomous.The frontend integrates a high-voltage driver, an integrated PGA and an offset-stabilized comparator in the receive path, a precision TDC for the time-of-flight measurement, amplitude measurement as well as an RDC unit for temperature measurement. In flow meter mode, the 32-bit CPU in combination with 4k of ROM code and 4k of NVRAM does the post processing for flow calculation. In time conversion mode the CPU is not active and the chip sends the raw time-of-flight data. It communicates to an external microcontroller via SPI interface. By means of the integrated pulse interface the AS6040 can run also in stand-alone mode.
The analog front-end is supported by an integrated charge pump to provide a programmable fire voltage in the range from 6 V o 17 V with a frequency from 50 kHz up to 1 MHz. The integrated PGA gain factor can be adjusted from 2 to 250. The first hit level detection starts with a programmable offset up to 220mV. After this is set down to 0 mV, the AS6040 can measure up to 31 zero crossings within a single receive burst. The front end achieves in single shot less than 300 ps rms noise single shot with good 500kHz transducers. The first-hit pulse width information and the amplitude can be used to regulate the first hit level, but also to get information about situations with bubbles or empty tubes. It comes in a compact QFN48 package and allows compact designs thanks to a small number of external components.