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Rapid high power transmit-receive switching using a timed cascade of PIN diodes
Christoph Michael Schildknecht1, Markus Weiger1, Romain Froidevaux1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zürich, Switzerland
For imaging of short-T2 samples often very short excitation pulses are desired, which requires high peak RF power. In this work, a transmit-receive switch is presented that can handle 18kW peak RF power and switches its state in less than 1µs.

Left: Illustration of the RF topology of the high-power T/R switch. The antiparallel PIN diode pairs are driven in a cascaded way. Towards the RX port, PIN diodes with shorter carrier lifetime are deployed.

Right: Implementation of such an RF topology. In addition, auxiliary circuits and low noise amplifier (LNA) can be seen.

Top row: transient switch behavior when switching from the TX to the RX state. The reverse bias is built up in a cascade, which reduces the transient voltage peaks.

Bottom row: Snippet out of the passive self-triggered PIN diode driver. As long as a PIN diode is still in its low impedance state, it has a forward voltage present, despite bulling a reverse current out of it. When the PIN diode changes to its high impedance state, current is drawn out of the next stage.