A high isolation switching unit for MRI system

The magnetic resonance imaging (MRI) system mainly consists of a large powerful magnet, a high power frequency tunable RF source, several receivers, L-C parallel resonance circuits, timing control unit, signal processing unit and a T/R switching unit. In order to protect the receivers from overload, and to obtain clear images the switching unit should meet the several requirements: low insertion, high isolation and fast switching speed.Such a switching unit with 1.5 Kilowatts handling capability is presented employing PIN diodes as key elements. This paper consists of four parts. (1) how to specify a PIN diode; (2) how to drive a PIN diode, and then presents a new method to drive PIN diode. It is no need to utilize neither optocoupler nor isolated power; (3) how to design a switch employing PIN diodes. (4) A simulation for the switch was performed to analyze its approximately specifications in advance and some measured results of the actual switch are shown.