A 36-Channel Auto-Calibrated Front-End ASIC for a pMUT-Based Miniaturized 3-D Ultrasound System

Abstract

We present an area-and power-efficient applicationspecific integrated circuit (ASIC) for a miniaturized 3-D ultrasound system. The ASIC is designed to transmit pulse and receive echo through a 36-channel 2-D piezoelectric Micromachined Ultrasound Transducer (pMUT) array. The 36-channel ASIC integrates a transmitter (TX), a receiver (RX), and an analog-todigital converter (ADC) within the 250-μm pitch channel while consuming low-power and supporting calibration to compensate for the process variation of the pMUT. The charge-recycling high-voltage TX (CRHV-TX) in standard CMOS generates up to 13.2-V PP pulse while reducing 42.2% peak TX power consumption. Also, each CRHV-TX automatically calibrates excitation voltage according to acoustic pressure of pMUT. The dynamic-bit-shared ADC (DBS-ADC) shares the most significant bits (MSBs) among four channels based on the signal similarity between adjacent channels. The analog front end (AFE) with a received signal sensitivity indicator (RSSI) changes its gain adaptively in real time depending on input signal strength. The ASIC consumes 1.14-mW/channel average power with 1-kHz pulse repetition frequency (PRF) and three TX pulses per cycle. The ASIC in 0.18-μm 1P6M Standard CMOS has been verified with both electrical and acoustic experiments with a 6 × 6 pMUT array.

Integrated Transceivers for Emerging Medical Ultrasound Imaging Devices: A Review

“…Adding extra digital buffers between the level-translators and the gates of HV transistors helps to speed up switching [26], but requires a floating ground at the voltage of HVDD-V GS , where V GS is the gate-source voltage of the HV transistor. Alternatively, some designs [29], [30] proposed to generate HV pulses using stacked LV transistors, but this is associated with increased circuit complexity and potential reliability concerns.…”

“…An alternative charge-recycling mechanism was proposed in [30], in which the two electrodes of a differential PMUT element are shorted to discharge the element, rather than switching both electrodes to ground. This helps to reduce the energy spent on charging and discharging parasitic capacitance to ground.…”

“…9d) [51] sense the current by establishing a low input impedance virtual ground. Therefore, in integrated systems, VA and TCA are usually used to interface with transducers with lower impedance (< 2 k ), such as PZTs [52], [53] and PMUTs [30], [46], while TIA and CA are commonly adopted for CMUTs and polyvinylidene fluorides (PVDF) transducers [54], [55] which often exhibit relatively higher impedance (> 10 k ) [56]. Note that the transducer impedance is a complex function of its physical dimension, material, fabrication process and acoustic load.…”

“…It has become increasingly clear that ADC techniques customized for ultrasound signal processing would be the key to enabling element-level digitization. Lee et al proposed a dynamic-bit-sharing technique based on the similarity of beamformed ultrasound signals, which allows adjacent element-level SAR ADCs in a 2×2 subarray to share the most-significant-bits, thus saving power [30]. Another hardware-sharing idea was proposed in [71], where a hybrid SAR/single-slope ADC shares its ramp generator with adjacent channels in a 2×2 subarray for area reduction.…”

Enhancing AlN PMUTs’ Acoustic Responsivity within a MEMS-on-CMOS Process

“…In addition, the CMOS process is limited to technologies that allow electrical contact from its last metal layer to the MEMS device within a specific post-process. Up until now, most of the reported PMUTs over CMOS are based on two-wafer bonding processes, in which the wafer with the PMUT (either AlN or PZT) is bonded to a CMOS wafer with analog front-end circuitry [10][11][12][13]. Despite the feasibility of this approach, the complexity of the bonding process and the limitations of the achievable fill factor impose some limitations.…”