Inverter-based 1 V analog front-end amplifiers in 90 nm CMOS for medical ultrasound imaging

Abstract

In this paper, we present the design and experimental evaluation of 1 V analog front-end amplifiers designed in 90 nm CMOS technology for capacitive micromachined ultrasound transducers (CMUTs) for medical ultrasound imaging systems. We propose two front-end amplifier topologies based on an inverter-based cascode amplifier; the first is a continuous time amplifier and the second is a charge sampling amplifier (CSA). The proposed front-end amplifiers are designed to amplify the signals from CMUTs in the frequency bandwidth from 15 to 45 MHz with a centre frequency of 30 MHz. From the measurements, the continuous time single-ended transimpedance amplifier achieves a voltage gain of 19 dB, an output noise power spectral density of 0.042 (lV)/ SQRT(Hz) at a centre-frequency of 30 MHz, and a total harmonic distortion of -23 dB at 450 mV p-p output voltage at 30 MHz input signal frequency. It draws only 598 lA per amplifier from a 1 V power supply. Its area measured only about 32 lm 9 32 lm per amplifier. On the other hand, a sampling based front-end amplifier [CSA] achieves a transfer gain of 17.4 dB at an input signal frequency of 30 MHz and an upper 3 dB cut-off frequency of 46 MHz at a sampling clock frequency of 100 MHz. It consumes 586 lA per amplifier from a 1 V power supply and achieves a signal-to-noise (SNR) ratio of 45.7 dB with a peak-to-peak output signal amplitude of 500 mV at a sampling frequency of 100 MHz. It occupies an area of 1470.2 lm 2 (which is equivalent to 38 lm 9 38 lm), which also includes the area of the switches for the CSA that will be used for the single CMUT element.