The design of an optically powered low voltage CMOS receiver for magnetic resonance imaging

This study proposes the design and layout of a fully differential, low-voltage CMOS low noise amplifier (LNA) and a mixer as a receiver for the radio frequency (RF) coils of magnetic resonance imaging (MRI) devices. The ultimate goal of the low-voltage design is to use an on-chip photodiode array as the power supply, which is expected to produce at least 0.9V supply voltage. The primary focus of the study is to achieve a sub-1 dB noise figure while maintaining sufficient gain and linearity, which are critical specifications due to the wide dynamic range of the MRI coils. The design constraints are interdependent, with gain, voltage swing, linearity, noise figure, and dynamic range being all related to each other. Consequently, achieving an optimal balance among these factors is a challenging but necessary task to ensure the system's effectiveness. The MRI coil is modeled as a voltage source with $50\Omega$ impedance. The LNA is noise-matched with the coil. The post-layout simulation of the LNA achieved a 26 dB voltage gain and a 0.71 dB noise figure. The downconversion mixer is designed in a folded structure to efficiently utilize the supply voltage. The mixer demonstrated a conversion gain of 10.6 dB, a third-order input intercept point (IIP3) of around 1.8 dBm, and an input-referred 1 dB compression point at approximately -13.4 dBm. The designs were implemented using 65nm technology. The overall system consumes 2.7 mW and achieves a noise figure of less than 1 dB, a voltage gain of 36 dB, an input-referred 1 dB compression point of -45 dBm, and a third-order input intercept point of -30 dBm.