Test & measurement
Figure 3: A conceptual block diagram of an NMR spectrometer where an RF pulse stimulates a sample inside the RF coil to emit an RF signal related to the element and molecular structure of the sample.
Another digitizer option that may be of value in this type of application is the digital pulse generator (DPG). The DPG option enables the digitizer to output up to four rectangular pulses with user-set periods, phases, and widths. The timing resolution of the pulses is based on the sampling clock. For instance, a DPG option installed in an M5i.33xx-x16 digitizer can output up to four pulse streams with a timing resolution of just 3.2 ns. The pulse generator operates in conjunction with the digitizer so that both operate simultaneously. One concern in handling long acquisition records is streaming this data to a host computer for further analysis and archiving.
The M5i digitizers utilize a 16-lane Gen3 PCIe bus capable of transferring data at rates up to 12.8 GB/s. This exceptional speed allows single-channel data acquired at a sampling rate of 6.4 GS/s to be streamed, in a FIFO process, directly to the computer with no data loss. Even faster sampling rates can be streamed without data loss using a new 8-bit transfer mode. The mode supports data streaming at acquisition rates of up to 10 GS/s from a single channel.
This example looked at a single T/R switch operation. Some NMRs use multiple RF coils arranged in phase arrays, and measurements on these systems may require more channels.
This, again, can be addressed using the Star-Hub option.
CONCLUSION
The Spectrum Instrumentation M5i.33xx-x16 digitizer family is well-matched to pulsed RF applications found in NMR, MRI and radar. They offer GHz bandwidths supported by up to 10 GS/s sampling rates with long acquisition record lengths. Optional capabilities include synchronizing multiple channels and even generating programmable pulse outputs.
Spectrum Instrumentation
spectrum-instrumentation.com
Figure 4: Analysis of a T/R switch RF input (upper left grid), gate signal (upper center grid), and the T/R switch output (upper right). 18 March 2024 Instrumentation Monthly
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