A CMUT read-out circuit with improved receive sensitivity using an adaptive biasing technique

In ultrasound imaging, capacitive micromachined ultrasonic transducer (CMUT) technology has been considered as a promising alternative for the conventional piezoelectric-based technology. Its advantages include better image quality, higher operational frequency and ease of fabrication and integration with CMOS read-out circuitry. This paper presents the design of an on-chip adaptive biasing unit which improves the sensitivity of the CMUT elements during the receive mode. This unit consists of a DC-DC converter to generate a range of bias voltage levels and a digital control unit to select the desired voltage. It is shown that by applying a different bias voltage during the transmit and receive modes, the receive sensitivity of the system is increased significantly, resulting in a better SNR and higher image quality.