CMOS based Q-switch for low-power pulsed14N quadruple resonance

Abstract

In order to reduce the recovery time of the nuclear quadrupole resonance probe (which implies the insertion of a dead time between the end of the pulse and the beginning of signal acquisition), several strategies have been proposed in the case of high-power radio frequency (rf) pulses. In fact, these strategies rely on a common principle, which is to lower, for an appropriate duration, the probe quality factor immediately after the transmit pulse. The quality factor is then restored for the receive period. In the case of a low-power rf pulses, we propose a very simple circuit that can alleviate the ringing following the rf pulse just by controlling a rf complementary metal-oxide-semiconductor (CMOS) switch inside the probe circuit. Such a technology features a low insertion loss and a low consumption, the switch being driven by a single-pin low voltage CMOS or transistor-transistor logic (TTL) control input. These properties are quite suitable for portable applications. Moreover, we have found that, for simple one-pulse experiments, this technology provides undistorted 14N quadrupole resonance spectra along with a significant improvement of the signal-to-noise ratio in the case of relatively broad lines involving a fine structure. © 2014 Wiley Periodicals, Inc.