A 16 /spl mu/A interface circuit for a capacitive-flow sensor

This mixed signal ASIC is for use with a fluidic oscillation element and differential capacitive pressure sensor. A chevron-shaped wall piece placed in the fluid vessel deflects the flow as described by the Coanda effect. Subject to design of the fluid passage, the flow changes over periodically, blocking itself from one side and forcing flow direction to the other. This changeover generates fluidic oscillation, proportional to flow rate. Two holes opened in the vessel above the turbulent areas transmit differential pressure to a capacitive pressure sensor. The ASIC converts the capacitive signal to a digital pulse train, filtering non-ideal components related to the mechanical structure. The pulse train is counted by a micropower host processor that makes the result available over telephone lines.