Low-Noise Low-Power Ultrasound AFE With Continuous TGC Built in Both TIA and Beamformer

This article presents a low-noise high-power-efficiency analog front-end (AFE) for capacitive-micromachined-ultrasonic transducers (CMUT). Implemented in 28-nm CMOS technology, the proposed AFE features three-stage continuous time-gain compensation (TGC) embedded in both trans-impedance amplifiers (TIAs) and an analog beamformer to provide a large compensation range with no extra power-consumption cost. The use of noise cancellation and capacitive feedback optimizes the noise performance of TIAs. The first stage of the TGC is built in the TIA by adjusting the positive and negative resistance loads, which are composed of voltage-controlled transistor arrays. An all-pass passive network is used as the delay unit of the analog beamformer, meanwhile achieving the second TGC stage. Phase shift for all frequency components in the ultrasound pass-band is manifested as a delay to the echoes. The third stage of the TGC is merged with a summing unit, which is a closed-loop amplifier with variable resistance feedback. The design takes into account the ability to handle large signals and power consumption, with TIA and beamforming operating at voltages of 2.5 V and 0.9 V, respectively. Experimental results show that the proposed AFE achieves a 2.11 pA/√Hz input-referred noise (IRN) at the 5 MHz center frequency of the echoes while consuming only 1.02 mW/channel. A total exponential TGC range of 60 dB with continuous ranges of 12 dB, 24 dB, and 24 dB assigned to three stages has been verified for this work.