This paper presents a pixel pitch-matched readout chip for 3-D photoacoustic (PA) imaging, featuring a dedicated signal conditioning and delta-sigma modulation integrated within a pixel area of 250 µm by 250 µm. The proof-of-concept receiver was implemented in an STMicroelectronics's 28-nm Fully Depleted Silicon On Insulator technology, and interfaces to a 4 × 4 subarray of capacitive micromachined ultrasound transducers (CMUTs). The front-end signal conditioning in each pixel employs a coarse/fine gain tuning architecture to fulfill the 90-dB dynamic range requirement of the application. The employed delta-sigma beamforming architecture obviates the need for area-consuming Nyquist ADCs and thereby enables an efficient in-pixel A/D conversion. The per-pixel switched-capacitor ΔΣ modulator leverages slewing-dominated and area-optimized inverter-based amplifiers. It occupies only 1/4th of the pixel, and its area compares favorably with state-of-the-art designs that offer the same SNR and bandwidth. The modulator's measured peak signal-to-noise-and-distortion ratio is 59.9 dB for a 10-MHz input bandwidth, and it consumes 6.65 mW from a 1-V supply. The overall subarray beamforming approach improves the area per channel by 7.4 times and the single-channel SNR by 8 dB compared to prior art with similar delay resolution and power dissipation. The functionality of the designed chip was evaluated within a PA imaging experiment, employing a flip-chip bonded 2-D CMUT array.
Keywords: 3-D photoacoustic (PA) imaging; CMOS; FDSOI; analog-to-digital conversion (ADC); capacitive micromachined ultrasound transducer (CMUT); delta-sigma modulation; matrix transducer array; subarray beamforming; ultrasound (US).