Design on amplitude control circuit for DDS signal source based on AD9834

Abstract

To ensure the proper operation of the Nuclear Magnetic Resonance Gyroscope (NMRG), a dedicated amplitude control circuit has been designed for the gas chamber. This circuit aims to fulfill the high-temperature heating requirements of the gas chamber, including achieving saturated vapor pressure, higher density, and ensuring the precise temperature stability of the gas chamber. The stability is of utmost importance as it directly impacts the accuracy of the NMRG. The circuit employs a voltage-output DAC1220, connected in series with a resistor, to drive the FS ADJUST pin of the AD9834. This configuration allows precise adjustment of the amplitude of the full-scale DAC current. The resulting signal is then amplified using a current-to-voltage conversion resistor and an Enhanced Howland Current Source (EHCS) circuit, effectively meeting the requirements for heating the gas chamber. The simulation and experiment show that the successful achievement of an AC sinusoidal heating signal with a frequency of 100KHz and a precise amplitude adjustment rangeof0-150mA.The adjustable step size of 0.01v ensures fine-tuned control. These findings validate that the heating signal fulfills the requirements for high-frequency electrical heating of the gas chamber in the NMRG.