| 摘要 |
In some embodiments, a nuclear magnetic resonance (NMR) receiver using digital downconversion and subsampling tracks transmit and/or receive signal phases according to time(s) elapsed since reference times (e.g. reset times) corresponding to known phases. Carrier-frequency (fc) NMR signals are digitized directly, using a sampling frequency (fs) lower than fc. Digital downconversion and carrier phase correction are performed to yield NMR modulations of interest. A phase determination circuit may include an N-bit counter incremented at fs and an associated count register storing an indicator of a time elapsed since a carrier generator reset for each transient sampling period start. A real-time controller synchronously resets the counters and corresponding signal generators. A sin/cos lookup table maps counts to phase correction function values. Described exemplary systems and methods allow applying phase correction(s) to detected NMR signals to compensate for system changes such as transmitter or downconverter NCO resets or carrier frequency changes. |
