A high-resolution reconfigurable sigma-delta Digital-to-Analog Converter for RF pulse transmission in MRI scanners

Abstract

In Magnetic Resonance Imaging (MRI) scanners Radio Frequency (RF) signals are important to accurately excite target tissues. RF signals depend on Digital-to-Analog Converter's (DAC) output which depends on sequence numbers issued from control room. This paper presents a sigma-delta modulator (SDM), followed by a DAC architecture that can be reconfigured while an MRI scanner is operating and pipelining is not required. The reconfigurable SDM is implemented in a 65nm CMOS technology and operates at an oversampling ratio (OSR) of 64 times. The modulator clocks at 2 GHz frequency with a 1.2-V supply voltage. The modulator occupies an area of 29 × 32 sq μm and consumes 319.1 mW. The proposed SDM-DAC is well-suited for the RF transmitter in the MRI scanner. The reconfigurability feature allows to select different resolutions for various types of RF pulses and can thereby target specific tissues more accurately. 1