ASIC - Application Specific Integrated Circuit  
The first prototypes of ultrasonic flow meters used a large amount of electronics for the precise determination of the ultrasonic transit times. Only the development of a custom chip (ASIC) allowed ndd the inexpensive application of this technology.
The following two pictures show the ndd ASIC in detail:
ASIC chip open
ASIC chip packaged
Direct view on the silicon
The ndd ASIC is housed
in a 44 pin PLCC case