Pulse Sequence Shaper For Radiospectroscopy And Relaxation Methods In NQR

Abstract

A pulse sequence shaper for the pursuance of the research using a wide spectrum of radiospectroscopy and relaxation methods in NQR is proposed. The distinctive feature of this product is its implementation with the application of a multi-functional programmable frequency synthesizer suitable for high-speed amplitude and phase manipulations.

Implementation of the Configuration Structure of an Integrated Computational Core of a Pulsed NQR Sensor Based on FPGA

“…This pulse activates the pulse counter in the sequence Pulse_counter:inst4, the source code of which from the output “ROM[4..0]” is fed to the non-volatile memory module ROM_module: inst17, and changing the level at the output “Pulse_out” leads to the activation of the video pulse generator Pulse_former:inst9. The operating principle of the latter is described in detail in [ 19 ]. Code words with data on the duration of the 90° pulse and the pause between the first and second pulses in the sequence are sent from the main interface controller (inst5 in Figure 3 ) to the inputs “Pulse[15..0]” and “Pause[26..0]”, respectively.…”

“…The key difference of the proposed solution is the ability to readjust the phase of the signal generated by the first channel with an accuracy of 1 degree and synchronize the initial phase of the generated radio pulses, with the leading edges of the video pulses arriving at the RF_pulse_In input from the output of the pulse train programmer ( Figure 5 ). The latter makes it possible to avoid the time-increasing errors of establishing the duration of the 90° and 180° excitation pulses of NQR, which occur when using classical incoherent techniques of radio pulse formation [ 19 , 27 ]. The modules LPM_Constant:inst15—LPM_Constant:inst18 and LPM_MUX:inst11 are used to provide quadrature phase manipulation.…”

“…In modern NQR observation equipment, special devices, namely pulse sequence shapers, are used to generate exciting radio pulses [ 19 , 20 ]. Such devices can be made in the form of special expansion cards for personal computers, or in the form of separate hardware units that connect to other units of the sensor: a radio frequency (RF) transmitter, a receive path, a synchronization unit and a data acquisition system (DAQ).…”

“…One of the most important characteristics of pulse sequence shapers is the accuracy of the formation of the duration of excitation radio pulses and the stability of their filling frequency. We already successfully developed an FPGA-based pulse sequence shaper for the NQR portable sensor [ 19 ]. In [ 21 ], we considered the implementation of a cheap digital pulse coherence spectrometer for the study of NQR in GaSe- and InSe-layered semiconductor crystals.…”

A Low-Cost Digital Pulsed Coherent Spectrometer for Investigation of NQR in Layered Semiconductor GaSe and InSe Crystals

“…In more detail, this block diagram and the principle of operation are described in paper [1]. Some parts and units of the proposed device are described in detail in papers [14][15][16][17][18][19].…”