Front-end processor using BBD distributed delay-sum architecture for micromachined ultrasonic sensor array

Micromachined technology makes it possible to integrate the ultrasonic sensor with the front-end processing circuit together, and make an ultrasonic system smart, compact and low cost. An ultrasonic sensor array with resonant frequency of about 60 kHz is fabricated for airborne applications, using sol-gel derived Pb(Zr,Ti)O₃ thin film and Si-based micromachining technique. The distributed delay-sum architecture based on a bucket brigade device (BBD) is employed for the beamforming of the sensor array in order to reduce chip area, simplify system design, improve power efficient and achieve monolithic integration. A charge attenuator is proposed to increase the dynamic range of the input signal and overcome the charge overflowing in bucket capacitors. A charge amplifier based preamplifier is used to interface the sensor array and beamformer. A prototype front-end processor shows good SNR with the dynamic range larger than 50 dB, and a beamforming performance consistent to the theoretical calculation very well.