GHz Ultrasonic Digital to Analog Converter for Wavefront Signal Processing

In this paper a Digital to Analog Converter (DAC) based on the propagation of ultrasonic waves in silicon is presented. AlN piezoelectric transducers on a silicon substrate are used to launch the ultrasonic pulses that propagate through the silicon and add coherently at a receiver transducer. The AlN transducer is actuated in the the thickness mode resonance frequency of 1.08GHz. The transmit transducer is formed into concentric rings which are binary weighted in area. The far field pressure magnitude is proportional to the transducer area. As a result, the sensed pressure from the binary-weighted rings is also binary weighted. A 4-bit version of the ultrasonic DAC is tested. The DAC has a resolution of 2.7mV., a range of 43 mV., DNL of 0.5 and INL of 0.4. The proposed DAC allows for controlling the ultrasonic wave amplitude without the need for large area., high power CMOS DAC. This device is useful for signal processing applications like computing 2D Fourier transform using ultrasonic wave propagation.