Supertex introduced the MD0107, a high-speed four channel auto damping device. The Supertex MD0107 is a high voltage device intended to improve the signal and image quality of ultrasound systems, and also the general signal quality with coaxial connections.
The MD0107 can be considered as a normally closed switch with a typical switch resistance of 35 ohms. In this state, the MD0107 ensures that any leakage currents are shunted to ground, while maintaining a low voltage drop. This low voltage level is beneficial as it ensures that the anti-parallel diodes in the transmit path remain off during the receive cycle of the system. Thus the anti-parallel diodes more effectively block the small signals and prevent transmitter noise from contaminating the receive signal.
During operation of the pulser, the MD0107 switch opens and thus presents high impedance to the transmitter pulse. The switch opens as soon as the voltage across it exceeds +/-2V and can withstand up to +/-130V. In this off-state, the MD0107 has very little effect on the transmit pulses or the power dissipated by the pulser.
The impedance of the MD0107, when the voltage across it is low, is suitable for terminating transmission lines. Where the line impedance is higher than the nominal 35 ohms of the MD0107, a series resistor can be added; for example terminating a ~75 ohm line can be effectively achieved by adding a 39 ohm resistor. Without correct line termination, reflections can cause higher signal loss and degrade image quality in ultrasound systems.