This paper presents a power- and area-efficient approach to digitizing the echo signals received by piezoelectric transducer elements, commonly used for ultrasound imaging. This technique utilizes such elements not only as sensors but also as the loop filter of an element-level δσ analog to digital converter (ADC). The receiver chain is thus greatly simplified, yielding savings in area and power. Every ADC becomes small enough to fit underneath a 150 μm × 150 μm transducer element, enabling simultaneous acquisition and digitization from all the elements in a 2-D array. This is especially valuable for miniature 3-D probes. Experimental results are reported for a prototype receiver chip with an array of 5×4 element-matched ADCs and a transducer array fabricated on top of the chip. Each ADC consumes 800 μW from a 1.8 V supply and achieves a SNR of 47 dB in a 75% bandwidth around a center frequency of 5 MHz.@en

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.@en