PS-15 Floating-Gate Based CMUT Sensing Circuit Using Capacitive Feedback Charge Amplifier

This paper describes the use of a floating-gate based capacitive feedback charge amplifier as a receive circuit for CMUT and investigates the charging effects. Detailed analysis of the capacitive sensing charge amplifier along with a floating-node charge adaptation circuit is presented. Compared with conventional approaches, using a charge amplifier, instead of a transimpedance amplifier, to detect capacitance variation avoids the dilemma of sensitivity-bandwidth trade-off. A version of the capacitive sensing charge amplifier is fabricated in a 0.5 mum CMOS process. The chip contains a 8-to-1 multiplexer and is interfaced with a CMUT annular-ring array, which is designed for forward-looking intravascular ultrasound imaging applications. Pulse-echo experiment is performed in an oil bath using a planar target 3 mm away from the array and the measurement result shows the signal-to-noise ratio of 16.65 dB with 122 muW power consumption around 3 MHz. In another implementation, channel hot electron (CHE) injection and Fowler-Nordheim tunneling currents are used to adjust the charge on the floating node and stabilize the output voltage. By using open-loop configuration, the leakage current of a CMUT device is characterized