A fully differential amplifier with CMOS feedback biasing for sensing CMUT signals

The paper illustrates design of a fully differential amplifier to sense current signals generated by CMUT for ultrasound imaging. Detection of reflected ultrasonic waves from body tissues requires low noise amplifier with wide input dynamic range. The transducer, being capacitive, isolates dc voltage from the input of the amplifier necessitating additional biasing circuit. In this work, a differential amplifier topology is chosen for its ability to reject common mode interference. Biasing is done by low frequency feedback using CMOS transistors which do not add significant noise to the system. The amplifier is designed in 0.18 μm CMOS process. Its input referred noise is 24.3 μV rms in the band 1-15 MHz. At 10 MHz it provides a gain of 25.5 dB with an input dynamic range of 62.5 dB. The amplifier consumes 314 μW of power with 1.8V-GND supply.