Front-end IC Design for 2D cMUT Arrays: Modeling and Experimental Verification

In this paper, we present the modeling, design and test of a front-end IC for 2D cMUT arrays. In the modeling phase, present simulation results for a front-end circuit integrated with an array transducer element, and compare these with the experimental result for a front-end IC for 2D cMUT array. The pulse-echo model for the transducer is a modified version of the Mason Equivalent Circuit where the radiation impedance term has been replaced by an RLC network to include the effects of finite transducer size and diffraction loss. The model has been verified by running transient simulations using ANSYS. The circuit was composed of a high voltage (50 Volt) pulse driver, a NMOS protection switch and a trans impedance amplifier. The IC was manufactured by AustriaMicroSystems AG, Graz, Austria, in 0.35 μm high-voltage CMOS technology. We wire bonded the IC to a cMUT element to test the overall circuit performance. The cMUT elements that we used in the experiments had an operating frequency of 10 MHz and consisted of 49 CMUT cells with an overall transducer area of 200×200 µm2. The applied DC bias was 70 Volts. The cMUTs were driven by a 40 Volts unipolar pulse. We first performed hydrophone measurements to verify the functionality of the driver circuit. A droplet of vegetable oil was used as the propagation medium for pulse-echo measurements. The echo was observed from the air-oil interface. The results show that the performance of the circuit was consistent with the simulations. We were able to receive an echo from the surface of an oil layer of thickness less than 0.5 mm. (approximately 1 μs round-trip flight time.) The overall layout size of the manufactured circuit is 170×170 µm2 and it is suitable for integration to 3-5 MHz cMUT elements.