Harvard College

Nan Sun

Donhee Ham

The Rabi frequency of oscillation of the nuclear magnetization vector of a sample in an NMR system may be controlled by modifying only the duty cycle of RF pulses delivered to the sample, without modifying the amplitude of the RF pulses, until the energy delivered at the Larmor frequency is adjusted to a desired amount. An impedance matching network between an NMR transceiver and an NMR coil may perform both power matching and noise matching simultaneously. During a transmission mode, the impedance matching network is connected to a transmitter portion of the transceiver, and the impedance of the coil is matched to the driver resistance. During a receiver mode, the impedance matching network is disconnected from the transmitter portion so that the impedance matching network remains connected only to the receiver portion, and signal-to-noise ratio in received NMR signals is maximized.

Systems and methods for design and construction of NMR transceiver circuits

Digital background calibration in a pipelined ADC is performed by extracting a capacitor mismatch value &#x394; that represents a mismatch between a sampling capacitor Cand a feedback capacitor Cin the pipelined ADC, and using &#x394; to correct the capacitor mismatch error. &#x394; is extracted by performing commutated feedback capacitor switching (CFCS) in a background correlation loop. The error caused by the capacitor mismatch is calibrated out by subtracting the error from a digital output Dof the pipelined ADC. Convergence speed may be accelerated and convergence accuracy may be increased during digital background calibration of pipelined ADCs, by using a higher order LPF. A bandwidth switching scheme may be implemented by the LPF, i.e. a larger bandwidth may be utilized during calibration start-up to increase convergence speed during start-up and a smaller bandwidth may be utilized during steady state to increase convergence accuracy during steady state.

Digital background calibration in pipelined ADCS

Methods and systems are described relating to dual-mode based digital background calibration of pipelined ADCs, for gain variations and device mismatches. Errors caused by gain insufficiency, nonlinearity, and capacitor mismatches are corrected by operating one ADC in two circuit configurations. These two modes are so arranged that their digital outputs differ in the presence of gain nonlinearity, gain insufficiency, and capacitor mismatches. The output difference is measured by randomly choosing one of the two operation modes at each sampling clock and digitally correlating the resulting digital output sequence. The measured output difference, which represents ADC errors, is used to remove the errors.

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Nan Sun