A Balanced T/R Switch for Wideband NMR Front-End

The transmit/receive (T/R) switch is crucial for the front-end of multi-nuclei nuclear magnetic resonance (NMR) spectrometers. However, the common designs of T/R switch nowadays are either inherently narrowband and/or have relatively long dead time, which significantly limits the overall system performance. To address this issue, we developed a PIN-diode-based T/R switch which features an active balanced receive path and a passive transmit path. A prototype of the T/R switch was constructed and experimentally characterized. The measurement results demonstrate that the switch has a bandwidth ranging from 10 to 330 MHz, maintaining an insertion loss from 0.09 to 0.18 dB and isolation from 54.1 to 83 dB. Moreover, the switch exhibits a very short turn-on dead time of 661.1 ns with a transient voltage of 3.3 mV and a turn-off dead time of 313.3 ns. The proposed design offers significant improvements in performance compared to existing T/R switch designs for multi-nuclei NMR spectrometers.