Feedback Biasing Based Adjustable Gain Ultrasound Preamplifier for CMUTs in 45nm CMOS

As CMOS technology is scaled down, supply voltages are decreasing and intrinsic gain of the nanoscale CMOS transistors is dropping while the threshold voltages of transistors are remaining relatively constant. In such scaled down nanoscale CMOS technologies, conventional vertical stacking architectures (for example. cascode architectures) for high-gain becomes no more attractive. In this paper we present the analysis and design of a feedback biasing based adjustable gain ultrasound preamplifier which is capable of amplifying signals from 15 MHz to 45 MHz from Capacitive Micromachined Ultrasound Transducers (CMUTs) in 45nm CMOS technology for medical ultrasound imaging applications. From the simulations, the proposed preamplifier achieves a voltage gain 27.47 dB at 30 MHz from the CMUT signal source to the output and this transfer gain can easily be varied from 27.47 dB to 3.21 dB by varying the control voltage without altering the power consumption. It exhibits an output noise power spectral density of 4.8 muV/SQR (Hz) at frequency of 30 MHz at maximum transfer gain. It consumes only 107 muA from a 900 mV power supply excluding bias currents.