Research On The Technology Of The Difference Frequency Detection Based On Phase-locked Loop

Difference frequency detection is the important testing part of photoelectric oscillation device, whose precision is decided by the precision of the difference frequency detection. Further study of high precision difference frequency detection technology is of great significance. Phase locked loop technique is an important technology to achieve difference frequency amplification, and its core is to reduce the loop phase noise as far as possible. A kind of low phase noise of phase-locked loop difference frequency amplification method is put forward based on the tiny difference frequency detection of photoelectric oscillation device.According to the system accuracy, this topic includes the system design. The phase lock loop as well as its phase noise has carried on the theoretical analysis and modeling simulation. Finally the correctness of the design is verified by experiment and D/Ata analysis. The topic mainly includes the following contents:1) System design and analysis of difference frequency detection. In this paper, the overall design objectives are determined according to the measurement range of photoelectric oscillation device. The overall scheme design is putted forward and the precision is analyzed according to the scheme design. Then find out the affecting factors, and provide theoretical basis for the follow-up circuit design.2) Phase noise modeling and simulation. The main factor affecting the system accuracy is the phase noise existing in the system. The transfer model and error equivalent model is established of phase noise in the phase-locked loop. By simulation the obvious factors that affecting the accuracy are under effective control. Finally, simulate noise impact according to the actual chip parameters, so as to provide theoretical basis for circuit design.3) Study of the input signal imitation and reference signal generation. In order to improve the stability and versatility of difference frequency amplifier, this paper presents a high-precision input signal simulation method. Parallel D/A is controlled by FPGA. Then through A/Ddition circuit controlling VCXO, precision analog frequency offset signal is produced. The reference signal is obtained by the atomic clock signal doubling by the clock chip.4) Study of multilevel amplification of differential frequency. For single-stage magnification will cause phase noise worse, the method of two stage amplification is put forward. In order to ensure that the funD/Amental frequency always remain unchanged after frequency doubling, each amplification includes three funD/Amental process:frequency transformation, filtering, frequency doubling process. At the same time, the loop bandwidth is strict controlled for the inhibition of the phase noise in the links of frequency doubling.Finally, set up the difference frequency detection system, and aimed at modeling simulation the experimental verification is needed. the related test scheme is designed. By testing and analysis the phase noise of each part, the feasibility of frequency detection can be guaranteed.