Design of a Transimpedance Amplifier for a Dual Mode CMUT Based Transcranial Ultrasound System

Monitoring and controlling the micro-bubble dy-namics in the the brain using their acoustic emissions is critical for utilizing their potential for imaging and therapy of brain diseases. Microbubbles pressure response can have harmonics and ultra-harmonics components. An adaptive Capacitive Micromachined Ultrasonic Transducers (CMUTs) with the ability to tune their active surface and frequency of operation could provide the required Signal-to-Noise Ratio (SNR) and directivity to perform image registration of the skull to CT images and monitoring the microbubble (MB) activity. The emitted single MB pressure level signal through the human skull is as low as 0.5 Pa in the 0.4 - 2 MHz frequency range and thus; transcranial MB activity monitoring requires a very low noise system. Transimpedance amplifier (TIA) with a lower input current noise level than the transducer noise can increase the SNR of the imaging system and detect the MB's acoustic emissions through the human skull. In this study, a low noise TIA, a band-gap reference (BGR) circuit, and an output buffer stage have been designed for single MB detection. The TIA has a gain of 117.8 dBΩ, 70 dB dynamic range with -3 dB bandwidth of 12.8 MHz and 312
$fA/\sqrt{Hz}$
input referred current noise density at 2 MHz with RMS input current noise of 1.28 nA in comparison with the CMUT element RMS current noise of 2.21 nA making it suitable for MBs activity monitoring.