G.I. Athanasopoulos

A high voltage pulser ASIC for driving high frequency ultrasonic arrays

This paper presents a high voltage integrated circuit (IC) that has been designed for connection to a hybrid printed circuit board (PCB) in close proximity to a polyvinyldenefluoride (PVdF) high resolution transducer array. An array of 16 pulser channels has been fabricated on chip; each channel provides an output train of -100 V pulses of 25 ns width, and fall and rise times of 6.3 ns and 13 ns, respectively, with a capacitive load of 2 pF.

Circuit design and simulation of a transmit beamforming ASIC for high-frequency ultrasonic imaging systems

This paper describes the design of a programmable transmit beamformer application-specific integrated circuit (ASIC) with 8 channels for ultrasound imaging systems. The system uses a 20-MHz reference clock. A digital delay-locked loop (DLL) was designed with 50 variable delay elements, each of which provides a clock with different phase from a single reference. Two phase detectors compare the phase difference of the reference clock with the feedback clock, adjusting the delay of the delay elements to bring the feedback clock signal in phase with the reference clock signal. Two independent control voltages for the delay elements ensure that the mark space ratio of the pulses remain at 50%. By combining a 10- bit asynchronous counter with the delays from the DLL, each channel can be programmed to give a maximum time delay of 51 μs with 1 ns resolution. It can also give bursts of up to 64 pulses. Finally, for a single pulse, it can adjust the pulse width between 9 ns and 100 ns by controlling the current flowing through a capacitor in a one-shot circuit, for use with 40-MHz and 5-MHz transducers, respectively.

Influence of processing conditions on the thermoelectric properties of La1-xSrxCoO3 (x=0, 0.05)

La1-xSrxCoO3 (x=0, 0.05) powders were prepared using the citrate-gel (Pechini) process. Pellets formed from these powders were sintered at various temperatures. All samples were characterized by means of X-Ray Diffraction and Scanning Electron Microscopy in order to investigate their structural and morphological properties. The electrical resistivity, thermal conductivity and thermopower were measured in a wide range of temperatures (2-350K) in order to understand the influence of the different processing conditions on the thermoelectric properties of the compounds.