Integrated Circuit CMOS Driver stage for Piezoelectric Ultrasound Imaging
One activity within the HE4T project has been the development of a driver stage for piezoelectric crystals that generate ultrasonic signals. This work can in energy harvesting context be used to facilitate the power supply of e.g. bio-implantable sensors that are implanted under the skin. In such application, ultrasound is used for both communication with and power supply to the sensor. An external transmitter communicates with a receiver with very small dimensions which is built into the sensor, and the energy to run the sensor is harvested from the receiver side. For increased power transfer capacity, especially in cases where a sensor has a certain implanted depth, it is advantageous to build the transmitter as an array of small piezoelectric devices, which allows to focus the transmitted energy to a single point. In such scenario, each transmitter device must be able to be excited and configured for signal reception independently of other devices. This enables control of the energy from the transmitter, as well as reception of the echoes that return from the sensor inside the body. Another area of use is in ultrasound imaging. The work with the driver stage investigated and made the design of transmitters/receivers for the piezoelectric units that make up the external transmitter array. The goal was to create the basis to be able to build this transmitter/receiver as a dedicated integrated circuit on a chip. Circuit level implementation as well as layout was done in a CMOS high voltage process. The proposed driver stage has a voltage swing of 100 Volts, at a DAC resolution of four bits with a rise time of 23 ns. The integrated circuits layout takes up an area of 228.6x235.44 μm2.
Complete layout of
the driver stage on an integrated circuit