Design And Implementation Of Signal Conditioning Circuit For Phase Noise Test System

With the development of time-frequency testing technology,phase noise has become an important content in the field of electronic measurement.At present,communication radar systems and radio frequency microwave systems have increasingly higher requirements for phase noise test systems.Therefore,the electronic measurement system with low noise,high stability,higher accuracy and higher reliability has good application prospects.The signal conditioning channel is an important component circuit of the phase noise test system to extract the phase noise of the frequency source.Its noise is the bottleneck restricting the development of the phase noise test system.This paper applies the theory of cross-correlation technology to the phase noise extraction circuit actually designed,which can greatly reduce the influence of uncorrelated noise factors on the channel,thereby reducing the noise floor of the phase noise test system and improving the sensitivity of the test system.In the thesis,the phase noise extraction circuit uses the direct homodyne method,and separate components are used to build a dual-channel phase noise extraction circuit and sampling circuit.The main research work of this paper is to design and realize the phase noise signal extraction circuit of the frequency source in the frequency range of 5-400 MHz.The research contents of the paper are as follows:1.According to the development requirements of the phase noise test system.Combining theory and simulation,the noise figure of the device in the phase noise signal conditioning circuit is estimated and analyzed,which mainly includes low noise operational amplifier and ADC noise figure analysis.2.Design of phase noise extraction circuit.Adopt ADI's AD797 low noise amplifier,design a cascade amplifier circuit,use Mini-Circuits' MPD-1+ and MPD-21+ phase discriminator,design a quadrature phase-locked network,in addition to the ADC clock circuit and The driving circuit is designed.3.The hardware design of the signal conditioning channel control circuit.With the help of the MCU as the control platform,the switching of the working state of the channel circuit of the phase noise test system is realized,the selection of the phase detection circuit of the source to be tested and the variable local oscillator signal and the adjustment of the gain amplification of the phase detection output signal are realized.4.Design of power circuit.Analyze the load voltage requirements of active devices in the signal conditioning channel,adopt distributed power supply scheme,make full use of the characteristics of high DC/DC switching power supply voltage conversion efficiency and low noise voltage output of LDO linear power supply,in addition from the device PCB From the perspective of layout,decoupling and shielding,the impact of external noise on the signal conditioning channel is reduced as much as possible.Finally,starting from the phase noise test system platform,with the help of corresponding test tools and equipment,the noise floor of the signal conditioning channel,the output noise of the power supply,and the phase noise test and result analysis of the 10 MHz frequency source are analyzed.