The Design Of Phase Noise Measurement System

Phase noise is an important indicator in the high frequency and high precision electronic system, which requires the phase noise measurement system of ultra-low phase noise floor to measure, in this paper the theory about two-port device phase noise measurement technology is studied and some experiments were carried out.Firstly, in order to facilitate principle the analysis and theoretical derivation of phase noise measurement system, the basis theory of phase noise is introduced. including the definition of phase noise power spectral density S?(f), the single sideband and double sideband phase noise power spectral density.Then the article describes the calibration procedure of classical phase noise measurement system, these steps have universal significance. For most measurement systems, in order to ensure the accuracy of mea-surement, the calibration is a necessary step.In this paper a series of phase noise measurement system are designed. At first, the classic saturation phase noise measurement system is set up, the noise index at lOGHz is -145dBrad2/Hz. The system's accuracy is limited by the low phase/voltage conversion gain and high noise floor of mixer. To solve this problem, there are two solutions.The first one is that reducing the influence of the noise floor of the measurement system, cross-correlation technique can effectively reduce system noise floor. Using two same measurement systems to measure the same DUT's phase noise, then the results take cross-correlation calculation and that can significantly reduce the background noise of single system. In the experiment, when using correlation techniques and the results are taken 100 average, the system noise floor is -155dBrad2/Hz at 10GHz. It is lOdB lower than the single channel measurement system. With the increase in the number of averaging, the slope characteristic-1 of 1/f noise in the results is more obviously, while the white noise curve smoother.The second solution is to improve the phase/voltage conversion gain of the measurement system, the interferometry method phase noise measurement system is design. This system can suppress the carrier by interference structure, thereby improving the phase/voltage conversion gain. In the experiments, the gain of interferometry phase noise measurement system is 28.5dBV2/rad2,the noise floor is-170dBrad2/Hz at 10GHz, far less than the classical phase noise measurement system.The interferometry phase noise measurement system has a good performance, however it is difficult to operate. In order to solve this problem, a semiautomatic measuring component of digitally phase shifters and attenuators is designed, the hardware and software of programmable digital phase shift and attenuation are developed and realized. The assembly consists of parallel port control circuit, a companion microcontroller program, and a computer window interface control program written by c#. This component can directly control the digital phase shifter and attenuator of the measurement system by the computer.