New MOSFET-Based Expander for High Frequency Ultrasound Systems

Diode-based expanders (expanders with single-crossed diodes) are widely used for pulse-echo measurements and in imaging systems. The function of the diode-based expander is to obstruct the noise from the transmitted output signals of the pulser and block the returned signals from the ultrasonic transducers to the pulser. It may also degrade the performance of the transducer and electronic components on the imaging side of the system because of non-linearity and attenuation at higher voltages. A new type of expander using power MOSFETs for high frequency ultrasound systems is proposed and studied. Compared to diode-based expander, this device is shown to yield lower insertion loss and total harmonic distortion, and faster reverse recovery time.