A transimpedance amplifier design for capacitive micromachined ultrasonic transducers operating at 7.5MHz
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Capacitive Micromachined Ultrasonic Transducers (CMUTs) are MEMS devices used in ultrasound imaging, e.g. ultrasound mammography. CMUT proved to be a viable transducer solution in ultrasound mammography without the hazardous effects of conventional X-ray mammography. The CMUTs have a very high electrical impedance, where a transimpedance amplifier (TIA) is most appropriate for preamplification during reception. A TIA with 25MHz bandwidth and 120kΩ transimpedance gain is designed on Cadence Virtuoso using XFAB XC06M3 process. The CMUT small signal model is used for 50μm radius and 7.5MHz operating frequency. This model is incorporated into TIA circuit simulations. Two design options are proposed for the TIA, one with the passive feedback resistor and the other with a MOSFET feedback resistor. The latter enabled us to save space in layout design compare to the former. Transient and noise simulations are conducted and compared for schematic and layout views. The input referred current noise of the TIA is simulated to be 0.5pA/√Hz and the power consumption is simulated to be approximately 3.3mW for both designs.