A High Voltage CMOS Transceiver for Low-Field NMR with a Maximum Output Current of 1.4 A<sub>pp</sub>
H. -P. Bürkle, Kevin Schmid, Tobias Klotz, Reiner Krapf, Jens Anders
Abstract
In this paper, we present a fully integrated transceiver ASIC for low field NMR spectroscopy. The chip integrates a conventional low intermediate frequency (low-IF) receiver together with a high-voltage (HV) H-bridge power amplifier (PA) and a PLL frequency synthesizer. The receiver consists of a low noise amplifier (LNA), a quadrature down-conversion mixer and a baseband amplifier. It achieves a measured input-referred voltage noise density of 1.1 nV/√Hz;. The integrated PLL frequency synthesizer supports operating frequencies between 4 MHz and 100 MHz, covering all relevant Larmor frequencies of benchtop and portable NMR. The on-chip PA can drive up to 1.4 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> into a 1Ω resistor and 1.6 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> into a 3mm, parallel-tuned NMR coil. When operating with a 3mm NMR coil inside a 1.45T unshimmed NMR magnet, the system achieves a spin sensitivity of 9.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> spins/√Hz and a concentration sensitivity of 1.79 mM/√Hz.