A Study On Key Technologies Of Automatic Measurement System For Residual Phase Noise

In various applications requiring frequency stability and good selectivity,such as Doppler radar and phase modulation communication,the phase noise of the system is very important.The phase noise of the system mainly comes from the frequency source oscillator.However,the residual phase noise of other two-port devices will also have a great impact on the system performance.The phase discrimination method is commonly used in the measurement of residual phase noise,which requires multiple functional devices,including double balanced mixer,power divider,attenuator,phase shifter,etc.In addition,the phase noise results are obtained by signal source analyzer or spectrum analyzer.Measurement requires complex systems and continuous calibration of measuring equipment,which is inefficient and costly.The key technologies of the automatic measurement system for residual phase noise is mainly studied in this paper.The measurement system,calibration procedure,and the automation of the measurement process are described along with strategies for reducing the measurement system noise floor in order to accurately make these measurements.In order to realize automatic measurement,a quadrature phase control module is designed to form a closed-loop system with phase discriminator and phase shifter.The quadrature phase module controls the phase shifter in real time so that the two input phases of the phase discriminator are automatically orthogonal,which improves the efficiency and reliability of measurement.Secondly,the MCU control module is designed to make the system alternate between the orthogonal and non-orthogonal states,so that the data needed for calculating the phase discrimination constant can be read in real time and transmitted to MATLAB through the serial module.Finally,in the orthogonal state,the sound card and the MATLAB program are used to complete the acquisition and data processing of the noise voltage.The hardware modules are integrated and encapsulated to make the whole measurement system become an independent and universal automatic measuring instrument for residual phase noise.The visual measurement operation interface and the result display of residual phase noise curve are realized by using MATLAB GUI.The noise floor and test function of the instrument are experimentally validated in this paper.By comparing with the dynamic analyzer,the feasibility and accuracy of using sound card to collect signals and using MATLAB to process noise voltage and acquire residual phase noise curve are verified.The circuit debugging,calibration and sensitivity measurement experiments of the automatic measuring instrument are carried out with Keil and Matlab software.Measurement results show that the instrument exhibits a phase noise floor of-166dBc/Hz at 96 kHz offset in the X-band frequency range.Finally,the residual phase noise of low noise amplifier HMC516 is measured by the automatic measuring instrument.The corresponding residual phase noise is-160.8dBc/Hz@95kHz(Pin=-10.6dBm)and-157.1dBc/Hz@95kHz Pin=0.74dBm).