Towards High-Throughput High-Frequency CMOS Nuclear Magnetic Resonance Spectroscopy

Driven by the many of Nuclear Magnetic Resonance (NMR) spectroscopy applications, there is an ever-increasing demand for high-throughput NMR receivers to accelerate the speed and reduce the cost of the NMR spectroscopy. The envisaged solution by the industry is to employ significantly stronger static magnetic fields to achieve higher signal-to-noise ratio (SNR). However, this demands for the system to operate at proportionally-higher frequencies to satisfy the Larmor equation and to be able to shrink the receiver coil size (hence, fit higher number of parallel receivers in the same space) without the loss of SNR. Despite the benefits, a higher frequency of operation introduces several challenges in the design of the receiver's transducer (i.e., coil) and the readout circuitry (i.e., tuning, matching, and amplification circuits). We present the design and optimization of an electromagnetic Radio Frequency (RF) coil along with the readout circuitry both integrated on the same silicon-based platform for fabrication in a standard 0.35-m complementary metal-oxide-semiconductor (CMOS) technology. In the design of the coil, all the important electrical and physical parameters that could affect the NMR spectroscopy's overall performance are analytically identified and taken into account. Additionally, the readout integrated circuit is designed to be compatible with a wide range of on-chip and off-chip coils. The circuit architecture and the design procedure proposed for the readout circuit are adaptable to any frequency of operation. The presented integrated system consists of two channels enabling simultaneous NMR spectroscopy, and has no practical limitations for channel scaling. To the best of our knowledge, this design is the first CMOS-based NMR receiver operating at 500 MHz. While all components are designed and optimized for this frequency, the presented design procedures for both the coil and the readout circuits are applicable to higher frequencies.