Design of CMOS transceiver for micro-NMR spectrometer

Abstract

Previously, the primary challenging issues in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) have been building coils with high quality factor (Q), or getting a strong magnetic field from the static magnet to increase the signal to noise ratio (SNR). Current techniques have enabled the development of palm-size to room-size of high-strength magnets magnetic field as well as high Q NMR coils. However, there still remains a strong effort to scale down NMR and MRI systems because RF transceivers built with discrete components leave the entire NMR system bulky. With the aid of modern RF CMOS technology, it is possible to integrate all RF blocks into one chip and significantly reduce the size of current NMR system.In this thesis, we will verify that miniaturization is possible with CMOS technologies and allows for the design of compact portable medical and chemical systems, and even implantable bio-sensors. To acquire NMR spectra from small objects, we will take advantage of the proximity between the sample and the sensor coil to make the system simpler. Three different chips were developed to show the possibilities of micro-NMR systems. In the first chip, a simple one-channel receiver was designed for sensing the $^{31}$P spectrum (around 86 MHz) from an adenosine triphosphate (ATP) sample at 5T. It uses a LNA-mixer hybrid circuit and a ring-type based frequency synthesizer with low power consumption. To do signal processing efficiently, a simple 2nd order Sigma-Delta analog-to-digital converter (ADC) for I and Q channels was added in the second chip. Like the first chip, we verified our design with the ATP sample. Based on experience gained from the first two designs, we extended the circuit and built an entire NMR transceiver to sense diverse NMR chemicals with a variety of frequencies. In the third chip. We designed a 5-300MHz multi-nuclei NMR transceiver designed with spectroscopy for drug discovery in mind. It includes a LNA, Mixer, VGA, fractional-N PLL, ADC and transmitter PA. Through these works, we will show the feasibility of micro NMR and MRI systems with low power and low cost CMOS integrated RF transceivers.