An Element-Matched Band-Pass Delta-Sigma ADC for Ultrasound Imaging

Abstract

This work presents a compact ADC architecture capable of digitizing the
signals received by every individual element of a 2D ultrasound
transducer array. An element-matched layout of 150 μm × 150 μm is
realized by exploiting each piezo-electric transducer element not only
as the signal source, but also as the electro-mechanical loop-filter of a
continuoustime band-pass ΔΣ ADC, thus minimizing the required circuit
blocks. The transducer's frequency response, which is inherently matched
with the signal bandwidth of interest, provides noise shaping to the
ADC. A prototype chip has been fabricated in a 0.18 μm CMOS technology,
featuring 20 ADCs located directly underneath a 150 μm-pitch
piezo-electric transducer array fabricated on top of the chip. Each ADC,
clocked at 200 MHz, consumes 800 μψ from a 1.8 V supply, and achieves
an SNR of 47 dB in a 75% bandwidth around a center frequency of 5 MHz.
Acoustic measurements show that the ADC successfully digitizes incoming
echo signals.