What are the challenges in AFE design?
Signal attenuation is one of the toughest aspects of AFE design. At 5 cm, a 10-MHz ultrasound signal is attenuated by 100 dB. Add an instantaneous dynamic range of about 60 dB, and the total dynamic range required is 160 dB. That’s why ultrasound uses so many channels. It takes a combination of time-gain control, channel summation, and filtering to produce good images. Also, Boltzman noise arises from the transducer and the human body, and it’s complicated by cable capacitance. Several generations of ADCs have been optimized for ultrasound. Generation one used a ladder attenuator and an external LNA. Generation two integrated the LNA, but needed dual supplies for noise performance. Generation-three ADCs use single +5-V supplies (with differential inputs to optimize dynamic range), integrate the LNA, and cut power use almost by half. They’re also designed for fast recovery from T/R-switch overload. What are the data-conversion design challenges? Beamforming is the function in which ADC
